1 /* -*- Mode: C; indent-tabs-mode:t ; c-basic-offset:8 -*- */
3 * I/O functions for libusb
4 * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
5 * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
6 * Copyright © 2019 Nathan Hjelm <hjelmn@cs.umm.edu>
7 * Copyright © 2019 Google LLC. All rights reserved.
9 * This library is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this library; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
32 #ifdef HAVE_SYS_TIME_H
35 #ifdef USBI_TIMERFD_AVAILABLE
37 #include <sys/timerfd.h>
44 * \page libusb_io Synchronous and asynchronous device I/O
46 * \section io_intro Introduction
48 * If you're using libusb in your application, you're probably wanting to
49 * perform I/O with devices - you want to perform USB data transfers.
51 * libusb offers two separate interfaces for device I/O. This page aims to
52 * introduce the two in order to help you decide which one is more suitable
53 * for your application. You can also choose to use both interfaces in your
54 * application by considering each transfer on a case-by-case basis.
56 * Once you have read through the following discussion, you should consult the
57 * detailed API documentation pages for the details:
58 * - \ref libusb_syncio
59 * - \ref libusb_asyncio
61 * \section theory Transfers at a logical level
63 * At a logical level, USB transfers typically happen in two parts. For
64 * example, when reading data from a endpoint:
65 * -# A request for data is sent to the device
66 * -# Some time later, the incoming data is received by the host
68 * or when writing data to an endpoint:
70 * -# The data is sent to the device
71 * -# Some time later, the host receives acknowledgement from the device that
72 * the data has been transferred.
74 * There may be an indefinite delay between the two steps. Consider a
75 * fictional USB input device with a button that the user can press. In order
76 * to determine when the button is pressed, you would likely submit a request
77 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
78 * Data will arrive when the button is pressed by the user, which is
79 * potentially hours later.
81 * libusb offers both a synchronous and an asynchronous interface to performing
82 * USB transfers. The main difference is that the synchronous interface
83 * combines both steps indicated above into a single function call, whereas
84 * the asynchronous interface separates them.
86 * \section sync The synchronous interface
88 * The synchronous I/O interface allows you to perform a USB transfer with
89 * a single function call. When the function call returns, the transfer has
90 * completed and you can parse the results.
92 * If you have used the libusb-0.1 before, this I/O style will seem familar to
93 * you. libusb-0.1 only offered a synchronous interface.
95 * In our input device example, to read button presses you might write code
96 * in the following style:
98 unsigned char data[4];
100 int r = libusb_bulk_transfer(dev_handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
101 if (r == 0 && actual_length == sizeof(data)) {
102 // results of the transaction can now be found in the data buffer
103 // parse them here and report button press
109 * The main advantage of this model is simplicity: you did everything with
110 * a single simple function call.
112 * However, this interface has its limitations. Your application will sleep
113 * inside libusb_bulk_transfer() until the transaction has completed. If it
114 * takes the user 3 hours to press the button, your application will be
115 * sleeping for that long. Execution will be tied up inside the library -
116 * the entire thread will be useless for that duration.
118 * Another issue is that by tieing up the thread with that single transaction
119 * there is no possibility of performing I/O with multiple endpoints and/or
120 * multiple devices simultaneously, unless you resort to creating one thread
123 * Additionally, there is no opportunity to cancel the transfer after the
124 * request has been submitted.
126 * For details on how to use the synchronous API, see the
127 * \ref libusb_syncio "synchronous I/O API documentation" pages.
129 * \section async The asynchronous interface
131 * Asynchronous I/O is the most significant new feature in libusb-1.0.
132 * Although it is a more complex interface, it solves all the issues detailed
135 * Instead of providing which functions that block until the I/O has complete,
136 * libusb's asynchronous interface presents non-blocking functions which
137 * begin a transfer and then return immediately. Your application passes a
138 * callback function pointer to this non-blocking function, which libusb will
139 * call with the results of the transaction when it has completed.
141 * Transfers which have been submitted through the non-blocking functions
142 * can be cancelled with a separate function call.
144 * The non-blocking nature of this interface allows you to be simultaneously
145 * performing I/O to multiple endpoints on multiple devices, without having
148 * This added flexibility does come with some complications though:
149 * - In the interest of being a lightweight library, libusb does not create
150 * threads and can only operate when your application is calling into it. Your
151 * application must call into libusb from it's main loop when events are ready
152 * to be handled, or you must use some other scheme to allow libusb to
153 * undertake whatever work needs to be done.
154 * - libusb also needs to be called into at certain fixed points in time in
155 * order to accurately handle transfer timeouts.
156 * - Memory handling becomes more complex. You cannot use stack memory unless
157 * the function with that stack is guaranteed not to return until the transfer
158 * callback has finished executing.
159 * - You generally lose some linearity from your code flow because submitting
160 * the transfer request is done in a separate function from where the transfer
161 * results are handled. This becomes particularly obvious when you want to
162 * submit a second transfer based on the results of an earlier transfer.
164 * Internally, libusb's synchronous interface is expressed in terms of function
165 * calls to the asynchronous interface.
167 * For details on how to use the asynchronous API, see the
168 * \ref libusb_asyncio "asynchronous I/O API" documentation pages.
173 * \page libusb_packetoverflow Packets and overflows
175 * \section packets Packet abstraction
177 * The USB specifications describe how data is transmitted in packets, with
178 * constraints on packet size defined by endpoint descriptors. The host must
179 * not send data payloads larger than the endpoint's maximum packet size.
181 * libusb and the underlying OS abstract out the packet concept, allowing you
182 * to request transfers of any size. Internally, the request will be divided
183 * up into correctly-sized packets. You do not have to be concerned with
184 * packet sizes, but there is one exception when considering overflows.
186 * \section overflow Bulk/interrupt transfer overflows
188 * When requesting data on a bulk endpoint, libusb requires you to supply a
189 * buffer and the maximum number of bytes of data that libusb can put in that
190 * buffer. However, the size of the buffer is not communicated to the device -
191 * the device is just asked to send any amount of data.
193 * There is no problem if the device sends an amount of data that is less than
194 * or equal to the buffer size. libusb reports this condition to you through
195 * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
198 * Problems may occur if the device attempts to send more data than can fit in
199 * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
200 * other behaviour is largely undefined: actual_length may or may not be
201 * accurate, the chunk of data that can fit in the buffer (before overflow)
202 * may or may not have been transferred.
204 * Overflows are nasty, but can be avoided. Even though you were told to
205 * ignore packets above, think about the lower level details: each transfer is
206 * split into packets (typically small, with a maximum size of 512 bytes).
207 * Overflows can only happen if the final packet in an incoming data transfer
208 * is smaller than the actual packet that the device wants to transfer.
209 * Therefore, you will never see an overflow if your transfer buffer size is a
210 * multiple of the endpoint's packet size: the final packet will either
211 * fill up completely or will be only partially filled.
215 * @defgroup libusb_asyncio Asynchronous device I/O
217 * This page details libusb's asynchronous (non-blocking) API for USB device
218 * I/O. This interface is very powerful but is also quite complex - you will
219 * need to read this page carefully to understand the necessary considerations
220 * and issues surrounding use of this interface. Simplistic applications
221 * may wish to consider the \ref libusb_syncio "synchronous I/O API" instead.
223 * The asynchronous interface is built around the idea of separating transfer
224 * submission and handling of transfer completion (the synchronous model
225 * combines both of these into one). There may be a long delay between
226 * submission and completion, however the asynchronous submission function
227 * is non-blocking so will return control to your application during that
228 * potentially long delay.
230 * \section asyncabstraction Transfer abstraction
232 * For the asynchronous I/O, libusb implements the concept of a generic
233 * transfer entity for all types of I/O (control, bulk, interrupt,
234 * isochronous). The generic transfer object must be treated slightly
235 * differently depending on which type of I/O you are performing with it.
237 * This is represented by the public libusb_transfer structure type.
239 * \section asynctrf Asynchronous transfers
241 * We can view asynchronous I/O as a 5 step process:
242 * -# <b>Allocation</b>: allocate a libusb_transfer
243 * -# <b>Filling</b>: populate the libusb_transfer instance with information
244 * about the transfer you wish to perform
245 * -# <b>Submission</b>: ask libusb to submit the transfer
246 * -# <b>Completion handling</b>: examine transfer results in the
247 * libusb_transfer structure
248 * -# <b>Deallocation</b>: clean up resources
251 * \subsection asyncalloc Allocation
253 * This step involves allocating memory for a USB transfer. This is the
254 * generic transfer object mentioned above. At this stage, the transfer
255 * is "blank" with no details about what type of I/O it will be used for.
257 * Allocation is done with the libusb_alloc_transfer() function. You must use
258 * this function rather than allocating your own transfers.
260 * \subsection asyncfill Filling
262 * This step is where you take a previously allocated transfer and fill it
263 * with information to determine the message type and direction, data buffer,
264 * callback function, etc.
266 * You can either fill the required fields yourself or you can use the
267 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
268 * and libusb_fill_interrupt_transfer().
270 * \subsection asyncsubmit Submission
272 * When you have allocated a transfer and filled it, you can submit it using
273 * libusb_submit_transfer(). This function returns immediately but can be
274 * regarded as firing off the I/O request in the background.
276 * \subsection asynccomplete Completion handling
278 * After a transfer has been submitted, one of four things can happen to it:
280 * - The transfer completes (i.e. some data was transferred)
281 * - The transfer has a timeout and the timeout expires before all data is
283 * - The transfer fails due to an error
284 * - The transfer is cancelled
286 * Each of these will cause the user-specified transfer callback function to
287 * be invoked. It is up to the callback function to determine which of the
288 * above actually happened and to act accordingly.
290 * The user-specified callback is passed a pointer to the libusb_transfer
291 * structure which was used to setup and submit the transfer. At completion
292 * time, libusb has populated this structure with results of the transfer:
293 * success or failure reason, number of bytes of data transferred, etc. See
294 * the libusb_transfer structure documentation for more information.
296 * <b>Important Note</b>: The user-specified callback is called from an event
297 * handling context. It is therefore important that no calls are made into
298 * libusb that will attempt to perform any event handling. Examples of such
299 * functions are any listed in the \ref libusb_syncio "synchronous API" and any of
300 * the blocking functions that retrieve \ref libusb_desc "USB descriptors".
302 * \subsection Deallocation
304 * When a transfer has completed (i.e. the callback function has been invoked),
305 * you are advised to free the transfer (unless you wish to resubmit it, see
306 * below). Transfers are deallocated with libusb_free_transfer().
308 * It is undefined behaviour to free a transfer which has not completed.
310 * \section asyncresubmit Resubmission
312 * You may be wondering why allocation, filling, and submission are all
313 * separated above where they could reasonably be combined into a single
316 * The reason for separation is to allow you to resubmit transfers without
317 * having to allocate new ones every time. This is especially useful for
318 * common situations dealing with interrupt endpoints - you allocate one
319 * transfer, fill and submit it, and when it returns with results you just
320 * resubmit it for the next interrupt.
322 * \section asynccancel Cancellation
324 * Another advantage of using the asynchronous interface is that you have
325 * the ability to cancel transfers which have not yet completed. This is
326 * done by calling the libusb_cancel_transfer() function.
328 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
329 * cancellation actually completes, the transfer's callback function will
330 * be invoked, and the callback function should check the transfer status to
331 * determine that it was cancelled.
333 * Freeing the transfer after it has been cancelled but before cancellation
334 * has completed will result in undefined behaviour.
336 * When a transfer is cancelled, some of the data may have been transferred.
337 * libusb will communicate this to you in the transfer callback. Do not assume
338 * that no data was transferred.
340 * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
342 * If your device does not have predictable transfer sizes (or it misbehaves),
343 * your application may submit a request for data on an IN endpoint which is
344 * smaller than the data that the device wishes to send. In some circumstances
345 * this will cause an overflow, which is a nasty condition to deal with. See
346 * the \ref libusb_packetoverflow page for discussion.
348 * \section asyncctrl Considerations for control transfers
350 * The <tt>libusb_transfer</tt> structure is generic and hence does not
351 * include specific fields for the control-specific setup packet structure.
353 * In order to perform a control transfer, you must place the 8-byte setup
354 * packet at the start of the data buffer. To simplify this, you could
355 * cast the buffer pointer to type struct libusb_control_setup, or you can
356 * use the helper function libusb_fill_control_setup().
358 * The wLength field placed in the setup packet must be the length you would
359 * expect to be sent in the setup packet: the length of the payload that
360 * follows (or the expected maximum number of bytes to receive). However,
361 * the length field of the libusb_transfer object must be the length of
362 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
363 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
365 * If you use the helper functions, this is simplified for you:
366 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
367 * data you are sending/requesting.
368 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
369 * request size as the wLength value (i.e. do not include the extra space you
370 * allocated for the control setup).
371 * -# If this is a host-to-device transfer, place the data to be transferred
372 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
373 * -# Call libusb_fill_control_transfer() to associate the data buffer with
374 * the transfer (and to set the remaining details such as callback and timeout).
375 * - Note that there is no parameter to set the length field of the transfer.
376 * The length is automatically inferred from the wLength field of the setup
378 * -# Submit the transfer.
380 * The multi-byte control setup fields (wValue, wIndex and wLength) must
381 * be given in little-endian byte order (the endianness of the USB bus).
382 * Endianness conversion is transparently handled by
383 * libusb_fill_control_setup() which is documented to accept host-endian
386 * Further considerations are needed when handling transfer completion in
387 * your callback function:
388 * - As you might expect, the setup packet will still be sitting at the start
389 * of the data buffer.
390 * - If this was a device-to-host transfer, the received data will be sitting
391 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
392 * - The actual_length field of the transfer structure is relative to the
393 * wLength of the setup packet, rather than the size of the data buffer. So,
394 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
395 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
396 * transferred in entirity.
398 * To simplify parsing of setup packets and obtaining the data from the
399 * correct offset, you may wish to use the libusb_control_transfer_get_data()
400 * and libusb_control_transfer_get_setup() functions within your transfer
403 * Even though control endpoints do not halt, a completed control transfer
404 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
405 * request was not supported.
407 * \section asyncintr Considerations for interrupt transfers
409 * All interrupt transfers are performed using the polling interval presented
410 * by the bInterval value of the endpoint descriptor.
412 * \section asynciso Considerations for isochronous transfers
414 * Isochronous transfers are more complicated than transfers to
415 * non-isochronous endpoints.
417 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
418 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
420 * During filling, set \ref libusb_transfer::type "type" to
421 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
422 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
423 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
424 * or equal to the number of packets you requested during allocation.
425 * libusb_alloc_transfer() does not set either of these fields for you, given
426 * that you might not even use the transfer on an isochronous endpoint.
428 * Next, populate the length field for the first num_iso_packets entries in
429 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
430 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
431 * packet length is determined by the wMaxPacketSize field in the endpoint
433 * Two functions can help you here:
435 * - libusb_get_max_iso_packet_size() is an easy way to determine the max
436 * packet size for an isochronous endpoint. Note that the maximum packet
437 * size is actually the maximum number of bytes that can be transmitted in
438 * a single microframe, therefore this function multiplies the maximum number
439 * of bytes per transaction by the number of transaction opportunities per
441 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
442 * within a transfer, which is usually what you want.
444 * For outgoing transfers, you'll obviously fill the buffer and populate the
445 * packet descriptors in hope that all the data gets transferred. For incoming
446 * transfers, you must ensure the buffer has sufficient capacity for
447 * the situation where all packets transfer the full amount of requested data.
449 * Completion handling requires some extra consideration. The
450 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
451 * is meaningless and should not be examined; instead you must refer to the
452 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
453 * each individual packet.
455 * The \ref libusb_transfer::status "status" field of the transfer is also a
457 * - If the packets were submitted and the isochronous data microframes
458 * completed normally, status will have value
459 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
460 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
461 * delays are not counted as transfer errors; the transfer.status field may
462 * indicate COMPLETED even if some or all of the packets failed. Refer to
463 * the \ref libusb_iso_packet_descriptor::status "status" field of each
464 * individual packet to determine packet failures.
465 * - The status field will have value
466 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
467 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
468 * - Other transfer status codes occur with normal behaviour.
470 * The data for each packet will be found at an offset into the buffer that
471 * can be calculated as if each prior packet completed in full. The
472 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
473 * functions may help you here.
475 * <b>Note</b>: Some operating systems (e.g. Linux) may impose limits on the
476 * length of individual isochronous packets and/or the total length of the
477 * isochronous transfer. Such limits can be difficult for libusb to detect,
478 * so the library will simply try and submit the transfer as set up by you.
479 * If the transfer fails to submit because it is too large,
480 * libusb_submit_transfer() will return
481 * \ref libusb_error::LIBUSB_ERROR_INVALID_PARAM "LIBUSB_ERROR_INVALID_PARAM".
483 * \section asyncmem Memory caveats
485 * In most circumstances, it is not safe to use stack memory for transfer
486 * buffers. This is because the function that fired off the asynchronous
487 * transfer may return before libusb has finished using the buffer, and when
488 * the function returns it's stack gets destroyed. This is true for both
489 * host-to-device and device-to-host transfers.
491 * The only case in which it is safe to use stack memory is where you can
492 * guarantee that the function owning the stack space for the buffer does not
493 * return until after the transfer's callback function has completed. In every
494 * other case, you need to use heap memory instead.
496 * \section asyncflags Fine control
498 * Through using this asynchronous interface, you may find yourself repeating
499 * a few simple operations many times. You can apply a bitwise OR of certain
500 * flags to a transfer to simplify certain things:
501 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
502 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
503 * less than the requested amount of data being marked with status
504 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
505 * (they would normally be regarded as COMPLETED)
506 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
507 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
508 * buffer when freeing the transfer.
509 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
510 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
511 * transfer after the transfer callback returns.
513 * \section asyncevent Event handling
515 * An asynchronous model requires that libusb perform work at various
516 * points in time - namely processing the results of previously-submitted
517 * transfers and invoking the user-supplied callback function.
519 * This gives rise to the libusb_handle_events() function which your
520 * application must call into when libusb has work do to. This gives libusb
521 * the opportunity to reap pending transfers, invoke callbacks, etc.
523 * There are 2 different approaches to dealing with libusb_handle_events:
525 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
527 * -# Integrate libusb with your application's main event loop. libusb
528 * exposes a set of file descriptors which allow you to do this.
530 * The first approach has the big advantage that it will also work on Windows
531 * were libusb' poll API for select / poll integration is not available. So
532 * if you want to support Windows and use the async API, you must use this
533 * approach, see the \ref eventthread "Using an event handling thread" section
536 * If you prefer a single threaded approach with a single central event loop,
537 * see the \ref libusb_poll "polling and timing" section for how to integrate libusb
538 * into your application's main event loop.
540 * \section eventthread Using an event handling thread
542 * Lets begin with stating the obvious: If you're going to use a separate
543 * thread for libusb event handling, your callback functions MUST be
546 * Other then that doing event handling from a separate thread, is mostly
547 * simple. You can use an event thread function as follows:
549 void *event_thread_func(void *ctx)
551 while (event_thread_run)
552 libusb_handle_events(ctx);
558 * There is one caveat though, stopping this thread requires setting the
559 * event_thread_run variable to 0, and after that libusb_handle_events() needs
560 * to return control to event_thread_func. But unless some event happens,
561 * libusb_handle_events() will not return.
563 * There are 2 different ways of dealing with this, depending on if your
564 * application uses libusb' \ref libusb_hotplug "hotplug" support or not.
566 * Applications which do not use hotplug support, should not start the event
567 * thread until after their first call to libusb_open(), and should stop the
568 * thread when closing the last open device as follows:
570 void my_close_handle(libusb_device_handle *dev_handle)
573 event_thread_run = 0;
575 libusb_close(dev_handle); // This wakes up libusb_handle_events()
578 pthread_join(event_thread);
584 * Applications using hotplug support should start the thread at program init,
585 * after having successfully called libusb_hotplug_register_callback(), and
586 * should stop the thread at program exit as follows:
588 void my_libusb_exit(void)
590 event_thread_run = 0;
591 libusb_hotplug_deregister_callback(ctx, hotplug_cb_handle); // This wakes up libusb_handle_events()
592 pthread_join(event_thread);
599 * @defgroup libusb_poll Polling and timing
601 * This page documents libusb's functions for polling events and timing.
602 * These functions are only necessary for users of the
603 * \ref libusb_asyncio "asynchronous API". If you are only using the simpler
604 * \ref libusb_syncio "synchronous API" then you do not need to ever call these
607 * The justification for the functionality described here has already been
608 * discussed in the \ref asyncevent "event handling" section of the
609 * asynchronous API documentation. In summary, libusb does not create internal
610 * threads for event processing and hence relies on your application calling
611 * into libusb at certain points in time so that pending events can be handled.
613 * Your main loop is probably already calling poll() or select() or a
614 * variant on a set of file descriptors for other event sources (e.g. keyboard
615 * button presses, mouse movements, network sockets, etc). You then add
616 * libusb's file descriptors to your poll()/select() calls, and when activity
617 * is detected on such descriptors you know it is time to call
618 * libusb_handle_events().
620 * There is one final event handling complication. libusb supports
621 * asynchronous transfers which time out after a specified time period.
623 * On some platforms a timerfd is used, so the timeout handling is just another
624 * fd, on other platforms this requires that libusb is called into at or after
625 * the timeout to handle it. So, in addition to considering libusb's file
626 * descriptors in your main event loop, you must also consider that libusb
627 * sometimes needs to be called into at fixed points in time even when there
628 * is no file descriptor activity, see \ref polltime details.
630 * In order to know precisely when libusb needs to be called into, libusb
631 * offers you a set of pollable file descriptors and information about when
632 * the next timeout expires.
634 * If you are using the asynchronous I/O API, you must take one of the two
635 * following options, otherwise your I/O will not complete.
637 * \section pollsimple The simple option
639 * If your application revolves solely around libusb and does not need to
640 * handle other event sources, you can have a program structure as follows:
643 // find and open device
644 // maybe fire off some initial async I/O
646 while (user_has_not_requested_exit)
647 libusb_handle_events(ctx);
652 * With such a simple main loop, you do not have to worry about managing
653 * sets of file descriptors or handling timeouts. libusb_handle_events() will
654 * handle those details internally.
656 * \section libusb_pollmain The more advanced option
658 * \note This functionality is currently only available on Unix-like platforms.
659 * On Windows, libusb_get_pollfds() simply returns NULL. Applications which
660 * want to support Windows are advised to use an \ref eventthread
661 * "event handling thread" instead.
663 * In more advanced applications, you will already have a main loop which
664 * is monitoring other event sources: network sockets, X11 events, mouse
665 * movements, etc. Through exposing a set of file descriptors, libusb is
666 * designed to cleanly integrate into such main loops.
668 * In addition to polling file descriptors for the other event sources, you
669 * take a set of file descriptors from libusb and monitor those too. When you
670 * detect activity on libusb's file descriptors, you call
671 * libusb_handle_events_timeout() in non-blocking mode.
673 * What's more, libusb may also need to handle events at specific moments in
674 * time. No file descriptor activity is generated at these times, so your
675 * own application needs to be continually aware of when the next one of these
676 * moments occurs (through calling libusb_get_next_timeout()), and then it
677 * needs to call libusb_handle_events_timeout() in non-blocking mode when
678 * these moments occur. This means that you need to adjust your
679 * poll()/select() timeout accordingly.
681 * libusb provides you with a set of file descriptors to poll and expects you
682 * to poll all of them, treating them as a single entity. The meaning of each
683 * file descriptor in the set is an internal implementation detail,
684 * platform-dependent and may vary from release to release. Don't try and
685 * interpret the meaning of the file descriptors, just do as libusb indicates,
686 * polling all of them at once.
688 * In pseudo-code, you want something that looks like:
692 libusb_get_pollfds(ctx)
693 while (user has not requested application exit) {
694 libusb_get_next_timeout(ctx);
695 poll(on libusb file descriptors plus any other event sources of interest,
696 using a timeout no larger than the value libusb just suggested)
697 if (poll() indicated activity on libusb file descriptors)
698 libusb_handle_events_timeout(ctx, &zero_tv);
699 if (time has elapsed to or beyond the libusb timeout)
700 libusb_handle_events_timeout(ctx, &zero_tv);
701 // handle events from other sources here
707 * \subsection polltime Notes on time-based events
709 * The above complication with having to track time and call into libusb at
710 * specific moments is a bit of a headache. For maximum compatibility, you do
711 * need to write your main loop as above, but you may decide that you can
712 * restrict the supported platforms of your application and get away with
713 * a more simplistic scheme.
715 * These time-based event complications are \b not required on the following
718 * - Linux, provided that the following version requirements are satisfied:
719 * - Linux v2.6.27 or newer, compiled with timerfd support
720 * - glibc v2.9 or newer
721 * - libusb v1.0.5 or newer
723 * Under these configurations, libusb_get_next_timeout() will \em always return
724 * 0, so your main loop can be simplified to:
728 libusb_get_pollfds(ctx)
729 while (user has not requested application exit) {
730 poll(on libusb file descriptors plus any other event sources of interest,
731 using any timeout that you like)
732 if (poll() indicated activity on libusb file descriptors)
733 libusb_handle_events_timeout(ctx, &zero_tv);
734 // handle events from other sources here
740 * Do remember that if you simplify your main loop to the above, you will
741 * lose compatibility with some platforms (including legacy Linux platforms,
742 * and <em>any future platforms supported by libusb which may have time-based
743 * event requirements</em>). The resultant problems will likely appear as
744 * strange bugs in your application.
746 * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
747 * check to see if it is safe to ignore the time-based event complications.
748 * If your application has taken the shortcut of ignoring libusb's next timeout
749 * in your main loop, then you are advised to check the return value of
750 * libusb_pollfds_handle_timeouts() during application startup, and to abort
751 * if the platform does suffer from these timing complications.
753 * \subsection fdsetchange Changes in the file descriptor set
755 * The set of file descriptors that libusb uses as event sources may change
756 * during the life of your application. Rather than having to repeatedly
757 * call libusb_get_pollfds(), you can set up notification functions for when
758 * the file descriptor set changes using libusb_set_pollfd_notifiers().
760 * \subsection mtissues Multi-threaded considerations
762 * Unfortunately, the situation is complicated further when multiple threads
763 * come into play. If two threads are monitoring the same file descriptors,
764 * the fact that only one thread will be woken up when an event occurs causes
767 * The events lock, event waiters lock, and libusb_handle_events_locked()
768 * entities are added to solve these problems. You do not need to be concerned
769 * with these entities otherwise.
771 * See the extra documentation: \ref libusb_mtasync
774 /** \page libusb_mtasync Multi-threaded applications and asynchronous I/O
776 * libusb is a thread-safe library, but extra considerations must be applied
777 * to applications which interact with libusb from multiple threads.
779 * The underlying issue that must be addressed is that all libusb I/O
780 * revolves around monitoring file descriptors through the poll()/select()
781 * system calls. This is directly exposed at the
782 * \ref libusb_asyncio "asynchronous interface" but it is important to note that the
783 * \ref libusb_syncio "synchronous interface" is implemented on top of the
784 * asynchonrous interface, therefore the same considerations apply.
786 * The issue is that if two or more threads are concurrently calling poll()
787 * or select() on libusb's file descriptors then only one of those threads
788 * will be woken up when an event arrives. The others will be completely
789 * oblivious that anything has happened.
791 * Consider the following pseudo-code, which submits an asynchronous transfer
792 * then waits for its completion. This style is one way you could implement a
793 * synchronous interface on top of the asynchronous interface (and libusb
794 * does something similar, albeit more advanced due to the complications
795 * explained on this page).
798 void cb(struct libusb_transfer *transfer)
800 int *completed = transfer->user_data;
805 struct libusb_transfer *transfer;
806 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE] __attribute__ ((aligned (2)));
809 transfer = libusb_alloc_transfer(0);
810 libusb_fill_control_setup(buffer,
811 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
812 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
813 libusb_submit_transfer(transfer);
816 poll(libusb file descriptors, 120*1000);
817 if (poll indicates activity)
818 libusb_handle_events_timeout(ctx, &zero_tv);
820 printf("completed!");
825 * Here we are <em>serializing</em> completion of an asynchronous event
826 * against a condition - the condition being completion of a specific transfer.
827 * The poll() loop has a long timeout to minimize CPU usage during situations
828 * when nothing is happening (it could reasonably be unlimited).
830 * If this is the only thread that is polling libusb's file descriptors, there
831 * is no problem: there is no danger that another thread will swallow up the
832 * event that we are interested in. On the other hand, if there is another
833 * thread polling the same descriptors, there is a chance that it will receive
834 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
835 * will only realise that the transfer has completed on the next iteration of
836 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
837 * undesirable, and don't even think about using short timeouts to circumvent
840 * The solution here is to ensure that no two threads are ever polling the
841 * file descriptors at the same time. A naive implementation of this would
842 * impact the capabilities of the library, so libusb offers the scheme
843 * documented below to ensure no loss of functionality.
845 * Before we go any further, it is worth mentioning that all libusb-wrapped
846 * event handling procedures fully adhere to the scheme documented below.
847 * This includes libusb_handle_events() and its variants, and all the
848 * synchronous I/O functions - libusb hides this headache from you.
850 * \section Using libusb_handle_events() from multiple threads
852 * Even when only using libusb_handle_events() and synchronous I/O functions,
853 * you can still have a race condition. You might be tempted to solve the
854 * above with libusb_handle_events() like so:
857 libusb_submit_transfer(transfer);
860 libusb_handle_events(ctx);
862 printf("completed!");
865 * This however has a race between the checking of completed and
866 * libusb_handle_events() acquiring the events lock, so another thread
867 * could have completed the transfer, resulting in this thread hanging
868 * until either a timeout or another event occurs. See also commit
869 * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
870 * synchronous API implementation of libusb.
872 * Fixing this race requires checking the variable completed only after
873 * taking the event lock, which defeats the concept of just calling
874 * libusb_handle_events() without worrying about locking. This is why
875 * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
876 * and libusb_handle_events_completed() functions, which handles doing the
877 * completion check for you after they have acquired the lock:
880 libusb_submit_transfer(transfer);
883 libusb_handle_events_completed(ctx, &completed);
885 printf("completed!");
888 * This nicely fixes the race in our example. Note that if all you want to
889 * do is submit a single transfer and wait for its completion, then using
890 * one of the synchronous I/O functions is much easier.
892 * \section eventlock The events lock
894 * The problem is when we consider the fact that libusb exposes file
895 * descriptors to allow for you to integrate asynchronous USB I/O into
896 * existing main loops, effectively allowing you to do some work behind
897 * libusb's back. If you do take libusb's file descriptors and pass them to
898 * poll()/select() yourself, you need to be aware of the associated issues.
900 * The first concept to be introduced is the events lock. The events lock
901 * is used to serialize threads that want to handle events, such that only
902 * one thread is handling events at any one time.
904 * You must take the events lock before polling libusb file descriptors,
905 * using libusb_lock_events(). You must release the lock as soon as you have
906 * aborted your poll()/select() loop, using libusb_unlock_events().
908 * \section threadwait Letting other threads do the work for you
910 * Although the events lock is a critical part of the solution, it is not
911 * enough on it's own. You might wonder if the following is sufficient...
913 libusb_lock_events(ctx);
915 poll(libusb file descriptors, 120*1000);
916 if (poll indicates activity)
917 libusb_handle_events_timeout(ctx, &zero_tv);
919 libusb_unlock_events(ctx);
921 * ...and the answer is that it is not. This is because the transfer in the
922 * code shown above may take a long time (say 30 seconds) to complete, and
923 * the lock is not released until the transfer is completed.
925 * Another thread with similar code that wants to do event handling may be
926 * working with a transfer that completes after a few milliseconds. Despite
927 * having such a quick completion time, the other thread cannot check that
928 * status of its transfer until the code above has finished (30 seconds later)
929 * due to contention on the lock.
931 * To solve this, libusb offers you a mechanism to determine when another
932 * thread is handling events. It also offers a mechanism to block your thread
933 * until the event handling thread has completed an event (and this mechanism
934 * does not involve polling of file descriptors).
936 * After determining that another thread is currently handling events, you
937 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
938 * You then re-check that some other thread is still handling events, and if
939 * so, you call libusb_wait_for_event().
941 * libusb_wait_for_event() puts your application to sleep until an event
942 * occurs, or until a thread releases the events lock. When either of these
943 * things happen, your thread is woken up, and should re-check the condition
944 * it was waiting on. It should also re-check that another thread is handling
945 * events, and if not, it should start handling events itself.
947 * This looks like the following, as pseudo-code:
950 if (libusb_try_lock_events(ctx) == 0) {
951 // we obtained the event lock: do our own event handling
953 if (!libusb_event_handling_ok(ctx)) {
954 libusb_unlock_events(ctx);
957 poll(libusb file descriptors, 120*1000);
958 if (poll indicates activity)
959 libusb_handle_events_locked(ctx, 0);
961 libusb_unlock_events(ctx);
963 // another thread is doing event handling. wait for it to signal us that
964 // an event has completed
965 libusb_lock_event_waiters(ctx);
968 // now that we have the event waiters lock, double check that another
969 // thread is still handling events for us. (it may have ceased handling
970 // events in the time it took us to reach this point)
971 if (!libusb_event_handler_active(ctx)) {
972 // whoever was handling events is no longer doing so, try again
973 libusb_unlock_event_waiters(ctx);
977 libusb_wait_for_event(ctx, NULL);
979 libusb_unlock_event_waiters(ctx);
981 printf("completed!\n");
984 * A naive look at the above code may suggest that this can only support
985 * one event waiter (hence a total of 2 competing threads, the other doing
986 * event handling), because the event waiter seems to have taken the event
987 * waiters lock while waiting for an event. However, the system does support
988 * multiple event waiters, because libusb_wait_for_event() actually drops
989 * the lock while waiting, and reaquires it before continuing.
991 * We have now implemented code which can dynamically handle situations where
992 * nobody is handling events (so we should do it ourselves), and it can also
993 * handle situations where another thread is doing event handling (so we can
994 * piggyback onto them). It is also equipped to handle a combination of
995 * the two, for example, another thread is doing event handling, but for
996 * whatever reason it stops doing so before our condition is met, so we take
997 * over the event handling.
999 * Four functions were introduced in the above pseudo-code. Their importance
1000 * should be apparent from the code shown above.
1001 * -# libusb_try_lock_events() is a non-blocking function which attempts
1002 * to acquire the events lock but returns a failure code if it is contended.
1003 * -# libusb_event_handling_ok() checks that libusb is still happy for your
1004 * thread to be performing event handling. Sometimes, libusb needs to
1005 * interrupt the event handler, and this is how you can check if you have
1006 * been interrupted. If this function returns 0, the correct behaviour is
1007 * for you to give up the event handling lock, and then to repeat the cycle.
1008 * The following libusb_try_lock_events() will fail, so you will become an
1009 * events waiter. For more information on this, read \ref fullstory below.
1010 * -# libusb_handle_events_locked() is a variant of
1011 * libusb_handle_events_timeout() that you can call while holding the
1012 * events lock. libusb_handle_events_timeout() itself implements similar
1013 * logic to the above, so be sure not to call it when you are
1014 * "working behind libusb's back", as is the case here.
1015 * -# libusb_event_handler_active() determines if someone is currently
1016 * holding the events lock
1018 * You might be wondering why there is no function to wake up all threads
1019 * blocked on libusb_wait_for_event(). This is because libusb can do this
1020 * internally: it will wake up all such threads when someone calls
1021 * libusb_unlock_events() or when a transfer completes (at the point after its
1022 * callback has returned).
1024 * \subsection fullstory The full story
1026 * The above explanation should be enough to get you going, but if you're
1027 * really thinking through the issues then you may be left with some more
1028 * questions regarding libusb's internals. If you're curious, read on, and if
1029 * not, skip to the next section to avoid confusing yourself!
1031 * The immediate question that may spring to mind is: what if one thread
1032 * modifies the set of file descriptors that need to be polled while another
1033 * thread is doing event handling?
1035 * There are 2 situations in which this may happen.
1036 * -# libusb_open() will add another file descriptor to the poll set,
1037 * therefore it is desirable to interrupt the event handler so that it
1038 * restarts, picking up the new descriptor.
1039 * -# libusb_close() will remove a file descriptor from the poll set. There
1040 * are all kinds of race conditions that could arise here, so it is
1041 * important that nobody is doing event handling at this time.
1043 * libusb handles these issues internally, so application developers do not
1044 * have to stop their event handlers while opening/closing devices. Here's how
1045 * it works, focusing on the libusb_close() situation first:
1047 * -# During initialization, libusb opens an internal pipe, and it adds the read
1048 * end of this pipe to the set of file descriptors to be polled.
1049 * -# During libusb_close(), libusb writes some dummy data on this event pipe.
1050 * This immediately interrupts the event handler. libusb also records
1051 * internally that it is trying to interrupt event handlers for this
1052 * high-priority event.
1053 * -# At this point, some of the functions described above start behaving
1055 * - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
1056 * OK for event handling to continue.
1057 * - libusb_try_lock_events() starts returning 1, indicating that another
1058 * thread holds the event handling lock, even if the lock is uncontended.
1059 * - libusb_event_handler_active() starts returning 1, indicating that
1060 * another thread is doing event handling, even if that is not true.
1061 * -# The above changes in behaviour result in the event handler stopping and
1062 * giving up the events lock very quickly, giving the high-priority
1063 * libusb_close() operation a "free ride" to acquire the events lock. All
1064 * threads that are competing to do event handling become event waiters.
1065 * -# With the events lock held inside libusb_close(), libusb can safely remove
1066 * a file descriptor from the poll set, in the safety of knowledge that
1067 * nobody is polling those descriptors or trying to access the poll set.
1068 * -# After obtaining the events lock, the close operation completes very
1069 * quickly (usually a matter of milliseconds) and then immediately releases
1071 * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
1072 * reverts to the original, documented behaviour.
1073 * -# The release of the events lock causes the threads that are waiting for
1074 * events to be woken up and to start competing to become event handlers
1075 * again. One of them will succeed; it will then re-obtain the list of poll
1076 * descriptors, and USB I/O will then continue as normal.
1078 * libusb_open() is similar, and is actually a more simplistic case. Upon a
1079 * call to libusb_open():
1081 * -# The device is opened and a file descriptor is added to the poll set.
1082 * -# libusb sends some dummy data on the event pipe, and records that it
1083 * is trying to modify the poll descriptor set.
1084 * -# The event handler is interrupted, and the same behaviour change as for
1085 * libusb_close() takes effect, causing all event handling threads to become
1087 * -# The libusb_open() implementation takes its free ride to the events lock.
1088 * -# Happy that it has successfully paused the events handler, libusb_open()
1089 * releases the events lock.
1090 * -# The event waiter threads are all woken up and compete to become event
1091 * handlers again. The one that succeeds will obtain the list of poll
1092 * descriptors again, which will include the addition of the new device.
1094 * \subsection concl Closing remarks
1096 * The above may seem a little complicated, but hopefully I have made it clear
1097 * why such complications are necessary. Also, do not forget that this only
1098 * applies to applications that take libusb's file descriptors and integrate
1099 * them into their own polling loops.
1101 * You may decide that it is OK for your multi-threaded application to ignore
1102 * some of the rules and locks detailed above, because you don't think that
1103 * two threads can ever be polling the descriptors at the same time. If that
1104 * is the case, then that's good news for you because you don't have to worry.
1105 * But be careful here; remember that the synchronous I/O functions do event
1106 * handling internally. If you have one thread doing event handling in a loop
1107 * (without implementing the rules and locking semantics documented above)
1108 * and another trying to send a synchronous USB transfer, you will end up with
1109 * two threads monitoring the same descriptors, and the above-described
1110 * undesirable behaviour occurring. The solution is for your polling thread to
1111 * play by the rules; the synchronous I/O functions do so, and this will result
1112 * in them getting along in perfect harmony.
1114 * If you do have a dedicated thread doing event handling, it is perfectly
1115 * legal for it to take the event handling lock for long periods of time. Any
1116 * synchronous I/O functions you call from other threads will transparently
1117 * fall back to the "event waiters" mechanism detailed above. The only
1118 * consideration that your event handling thread must apply is the one related
1119 * to libusb_event_handling_ok(): you must call this before every poll(), and
1120 * give up the events lock if instructed.
1123 int usbi_io_init(struct libusb_context *ctx)
1127 usbi_mutex_init(&ctx->flying_transfers_lock);
1128 usbi_mutex_init(&ctx->events_lock);
1129 usbi_mutex_init(&ctx->event_waiters_lock);
1130 usbi_cond_init(&ctx->event_waiters_cond);
1131 usbi_mutex_init(&ctx->event_data_lock);
1132 usbi_tls_key_create(&ctx->event_handling_key);
1133 list_init(&ctx->flying_transfers);
1134 list_init(&ctx->ipollfds);
1135 list_init(&ctx->removed_ipollfds);
1136 list_init(&ctx->hotplug_msgs);
1137 list_init(&ctx->completed_transfers);
1139 /* FIXME should use an eventfd on kernels that support it */
1140 r = usbi_pipe(ctx->event_pipe);
1142 r = LIBUSB_ERROR_OTHER;
1146 r = usbi_add_pollfd(ctx, ctx->event_pipe[0], POLLIN);
1148 goto err_close_pipe;
1150 #ifdef USBI_TIMERFD_AVAILABLE
1151 ctx->timerfd = timerfd_create(usbi_backend.get_timerfd_clockid(),
1152 TFD_NONBLOCK | TFD_CLOEXEC);
1153 if (ctx->timerfd >= 0) {
1154 usbi_dbg("using timerfd for timeouts");
1155 r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
1157 goto err_close_timerfd;
1159 usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
1166 #ifdef USBI_TIMERFD_AVAILABLE
1168 close(ctx->timerfd);
1169 usbi_remove_pollfd(ctx, ctx->event_pipe[0]);
1172 usbi_close(ctx->event_pipe[0]);
1173 usbi_close(ctx->event_pipe[1]);
1175 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1176 usbi_mutex_destroy(&ctx->events_lock);
1177 usbi_mutex_destroy(&ctx->event_waiters_lock);
1178 usbi_cond_destroy(&ctx->event_waiters_cond);
1179 usbi_mutex_destroy(&ctx->event_data_lock);
1180 usbi_tls_key_delete(ctx->event_handling_key);
1184 static void cleanup_removed_pollfds(struct libusb_context *ctx)
1186 struct usbi_pollfd *ipollfd, *tmp;
1187 list_for_each_entry_safe(ipollfd, tmp, &ctx->removed_ipollfds, list, struct usbi_pollfd) {
1188 list_del(&ipollfd->list);
1193 void usbi_io_exit(struct libusb_context *ctx)
1195 usbi_remove_pollfd(ctx, ctx->event_pipe[0]);
1196 usbi_close(ctx->event_pipe[0]);
1197 usbi_close(ctx->event_pipe[1]);
1198 #ifdef USBI_TIMERFD_AVAILABLE
1199 if (usbi_using_timerfd(ctx)) {
1200 usbi_remove_pollfd(ctx, ctx->timerfd);
1201 close(ctx->timerfd);
1204 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1205 usbi_mutex_destroy(&ctx->events_lock);
1206 usbi_mutex_destroy(&ctx->event_waiters_lock);
1207 usbi_cond_destroy(&ctx->event_waiters_cond);
1208 usbi_mutex_destroy(&ctx->event_data_lock);
1209 usbi_tls_key_delete(ctx->event_handling_key);
1211 cleanup_removed_pollfds(ctx);
1214 static int calculate_timeout(struct usbi_transfer *transfer)
1217 struct timespec current_time;
1218 unsigned int timeout =
1219 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
1222 timerclear(&transfer->timeout);
1226 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, ¤t_time);
1228 usbi_err(ITRANSFER_CTX(transfer),
1229 "failed to read monotonic clock, errno=%d", errno);
1233 current_time.tv_sec += timeout / 1000;
1234 current_time.tv_nsec += (timeout % 1000) * 1000000;
1236 while (current_time.tv_nsec >= 1000000000) {
1237 current_time.tv_nsec -= 1000000000;
1238 current_time.tv_sec++;
1241 TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
1245 /** \ingroup libusb_asyncio
1246 * Allocate a libusb transfer with a specified number of isochronous packet
1247 * descriptors. The returned transfer is pre-initialized for you. When the new
1248 * transfer is no longer needed, it should be freed with
1249 * libusb_free_transfer().
1251 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
1252 * interrupt) should specify an iso_packets count of zero.
1254 * For transfers intended for isochronous endpoints, specify an appropriate
1255 * number of packet descriptors to be allocated as part of the transfer.
1256 * The returned transfer is not specially initialized for isochronous I/O;
1257 * you are still required to set the
1258 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
1259 * \ref libusb_transfer::type "type" fields accordingly.
1261 * It is safe to allocate a transfer with some isochronous packets and then
1262 * use it on a non-isochronous endpoint. If you do this, ensure that at time
1263 * of submission, num_iso_packets is 0 and that type is set appropriately.
1265 * \param iso_packets number of isochronous packet descriptors to allocate. Must be non-negative.
1266 * \returns a newly allocated transfer, or NULL on error
1269 struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
1272 struct libusb_transfer *transfer;
1273 size_t os_alloc_size;
1275 struct usbi_transfer *itransfer;
1277 assert(iso_packets >= 0);
1279 os_alloc_size = usbi_backend.transfer_priv_size;
1280 alloc_size = sizeof(struct usbi_transfer)
1281 + sizeof(struct libusb_transfer)
1282 + (sizeof(struct libusb_iso_packet_descriptor) * (size_t)iso_packets)
1284 itransfer = calloc(1, alloc_size);
1288 itransfer->num_iso_packets = iso_packets;
1289 usbi_mutex_init(&itransfer->lock);
1290 transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1291 usbi_dbg("transfer %p", transfer);
1295 /** \ingroup libusb_asyncio
1296 * Free a transfer structure. This should be called for all transfers
1297 * allocated with libusb_alloc_transfer().
1299 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
1300 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
1301 * non-NULL, this function will also free the transfer buffer using the
1302 * standard system memory allocator (e.g. free()).
1304 * It is legal to call this function with a NULL transfer. In this case,
1305 * the function will simply return safely.
1307 * It is not legal to free an active transfer (one which has been submitted
1308 * and has not yet completed).
1310 * \param transfer the transfer to free
1312 void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
1314 struct usbi_transfer *itransfer;
1318 usbi_dbg("transfer %p", transfer);
1319 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER)
1320 free(transfer->buffer);
1322 itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1323 usbi_mutex_destroy(&itransfer->lock);
1327 #ifdef USBI_TIMERFD_AVAILABLE
1328 static int disarm_timerfd(struct libusb_context *ctx)
1330 const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
1334 r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
1336 return LIBUSB_ERROR_OTHER;
1341 /* iterates through the flying transfers, and rearms the timerfd based on the
1342 * next upcoming timeout.
1343 * must be called with flying_list locked.
1344 * returns 0 on success or a LIBUSB_ERROR code on failure.
1346 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1348 struct usbi_transfer *transfer;
1350 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1351 struct timeval *cur_tv = &transfer->timeout;
1353 /* if we've reached transfers of infinite timeout, then we have no
1355 if (!timerisset(cur_tv))
1358 /* act on first transfer that has not already been handled */
1359 if (!(transfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))) {
1361 const struct itimerspec it = { {0, 0},
1362 { cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
1363 usbi_dbg("next timeout originally %dms", USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1364 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1366 return LIBUSB_ERROR_OTHER;
1372 return disarm_timerfd(ctx);
1375 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1382 /* add a transfer to the (timeout-sorted) active transfers list.
1383 * This function will return non 0 if fails to update the timer,
1384 * in which case the transfer is *not* on the flying_transfers list. */
1385 static int add_to_flying_list(struct usbi_transfer *transfer)
1387 struct usbi_transfer *cur;
1388 struct timeval *timeout = &transfer->timeout;
1389 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1393 r = calculate_timeout(transfer);
1397 /* if we have no other flying transfers, start the list with this one */
1398 if (list_empty(&ctx->flying_transfers)) {
1399 list_add(&transfer->list, &ctx->flying_transfers);
1403 /* if we have infinite timeout, append to end of list */
1404 if (!timerisset(timeout)) {
1405 list_add_tail(&transfer->list, &ctx->flying_transfers);
1406 /* first is irrelevant in this case */
1410 /* otherwise, find appropriate place in list */
1411 list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
1412 /* find first timeout that occurs after the transfer in question */
1413 struct timeval *cur_tv = &cur->timeout;
1415 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
1416 (cur_tv->tv_sec == timeout->tv_sec &&
1417 cur_tv->tv_usec > timeout->tv_usec)) {
1418 list_add_tail(&transfer->list, &cur->list);
1423 /* first is 0 at this stage (list not empty) */
1425 /* otherwise we need to be inserted at the end */
1426 list_add_tail(&transfer->list, &ctx->flying_transfers);
1428 #ifdef USBI_TIMERFD_AVAILABLE
1429 if (first && usbi_using_timerfd(ctx) && timerisset(timeout)) {
1430 /* if this transfer has the lowest timeout of all active transfers,
1431 * rearm the timerfd with this transfer's timeout */
1432 const struct itimerspec it = { {0, 0},
1433 { timeout->tv_sec, timeout->tv_usec * 1000 } };
1434 usbi_dbg("arm timerfd for timeout in %dms (first in line)",
1435 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1436 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1438 usbi_warn(ctx, "failed to arm first timerfd (errno %d)", errno);
1439 r = LIBUSB_ERROR_OTHER;
1447 list_del(&transfer->list);
1452 /* remove a transfer from the active transfers list.
1453 * This function will *always* remove the transfer from the
1454 * flying_transfers list. It will return a LIBUSB_ERROR code
1455 * if it fails to update the timer for the next timeout. */
1456 static int remove_from_flying_list(struct usbi_transfer *transfer)
1458 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1462 usbi_mutex_lock(&ctx->flying_transfers_lock);
1463 rearm_timerfd = (timerisset(&transfer->timeout) &&
1464 list_first_entry(&ctx->flying_transfers, struct usbi_transfer, list) == transfer);
1465 list_del(&transfer->list);
1466 if (usbi_using_timerfd(ctx) && rearm_timerfd)
1467 r = arm_timerfd_for_next_timeout(ctx);
1468 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1473 /** \ingroup libusb_asyncio
1474 * Submit a transfer. This function will fire off the USB transfer and then
1475 * return immediately.
1477 * \param transfer the transfer to submit
1478 * \returns 0 on success
1479 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
1480 * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
1481 * \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
1482 * by the operating system.
1483 * \returns LIBUSB_ERROR_INVALID_PARAM if the transfer size is larger than
1484 * the operating system and/or hardware can support
1485 * \returns another LIBUSB_ERROR code on other failure
1487 int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
1489 struct usbi_transfer *itransfer =
1490 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1491 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1494 usbi_dbg("transfer %p", transfer);
1497 * Important note on locking, this function takes / releases locks
1498 * in the following order:
1499 * take flying_transfers_lock
1500 * take itransfer->lock
1502 * add to flying_transfers list
1503 * release flying_transfers_lock
1505 * release itransfer->lock
1507 * take flying_transfers_lock
1508 * remove from flying_transfers list
1509 * release flying_transfers_lock
1511 * Note that it takes locks in the order a-b and then releases them
1512 * in the same order a-b. This is somewhat unusual but not wrong,
1513 * release order is not important as long as *all* locks are released
1514 * before re-acquiring any locks.
1516 * This means that the ordering of first releasing itransfer->lock
1517 * and then re-acquiring the flying_transfers_list on error is
1518 * important and must not be changed!
1520 * This is done this way because when we take both locks we must always
1521 * take flying_transfers_lock first to avoid ab-ba style deadlocks with
1522 * the timeout handling and usbi_handle_disconnect paths.
1524 * And we cannot release itransfer->lock before the submission is
1525 * complete otherwise timeout handling for transfers with short
1526 * timeouts may run before submission.
1528 usbi_mutex_lock(&ctx->flying_transfers_lock);
1529 usbi_mutex_lock(&itransfer->lock);
1530 if (itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT) {
1531 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1532 usbi_mutex_unlock(&itransfer->lock);
1533 return LIBUSB_ERROR_BUSY;
1535 itransfer->transferred = 0;
1536 itransfer->state_flags = 0;
1537 itransfer->timeout_flags = 0;
1538 r = add_to_flying_list(itransfer);
1540 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1541 usbi_mutex_unlock(&itransfer->lock);
1545 * We must release the flying transfers lock here, because with
1546 * some backends the submit_transfer method is synchroneous.
1548 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1550 r = usbi_backend.submit_transfer(itransfer);
1551 if (r == LIBUSB_SUCCESS) {
1552 itransfer->state_flags |= USBI_TRANSFER_IN_FLIGHT;
1553 /* keep a reference to this device */
1554 libusb_ref_device(transfer->dev_handle->dev);
1556 usbi_mutex_unlock(&itransfer->lock);
1558 if (r != LIBUSB_SUCCESS)
1559 remove_from_flying_list(itransfer);
1564 /** \ingroup libusb_asyncio
1565 * Asynchronously cancel a previously submitted transfer.
1566 * This function returns immediately, but this does not indicate cancellation
1567 * is complete. Your callback function will be invoked at some later time
1568 * with a transfer status of
1569 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
1570 * "LIBUSB_TRANSFER_CANCELLED."
1572 * \param transfer the transfer to cancel
1573 * \returns 0 on success
1574 * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is not in progress,
1575 * already complete, or already cancelled.
1576 * \returns a LIBUSB_ERROR code on failure
1578 int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
1580 struct usbi_transfer *itransfer =
1581 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1584 usbi_dbg("transfer %p", transfer );
1585 usbi_mutex_lock(&itransfer->lock);
1586 if (!(itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT)
1587 || (itransfer->state_flags & USBI_TRANSFER_CANCELLING)) {
1588 r = LIBUSB_ERROR_NOT_FOUND;
1591 r = usbi_backend.cancel_transfer(itransfer);
1593 if (r != LIBUSB_ERROR_NOT_FOUND &&
1594 r != LIBUSB_ERROR_NO_DEVICE)
1595 usbi_err(TRANSFER_CTX(transfer),
1596 "cancel transfer failed error %d", r);
1598 usbi_dbg("cancel transfer failed error %d", r);
1600 if (r == LIBUSB_ERROR_NO_DEVICE)
1601 itransfer->state_flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
1604 itransfer->state_flags |= USBI_TRANSFER_CANCELLING;
1607 usbi_mutex_unlock(&itransfer->lock);
1611 /** \ingroup libusb_asyncio
1612 * Set a transfers bulk stream id. Note users are advised to use
1613 * libusb_fill_bulk_stream_transfer() instead of calling this function
1616 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1618 * \param transfer the transfer to set the stream id for
1619 * \param stream_id the stream id to set
1620 * \see libusb_alloc_streams()
1622 void API_EXPORTED libusb_transfer_set_stream_id(
1623 struct libusb_transfer *transfer, uint32_t stream_id)
1625 struct usbi_transfer *itransfer =
1626 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1628 itransfer->stream_id = stream_id;
1631 /** \ingroup libusb_asyncio
1632 * Get a transfers bulk stream id.
1634 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1636 * \param transfer the transfer to get the stream id for
1637 * \returns the stream id for the transfer
1639 uint32_t API_EXPORTED libusb_transfer_get_stream_id(
1640 struct libusb_transfer *transfer)
1642 struct usbi_transfer *itransfer =
1643 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1645 return itransfer->stream_id;
1648 /* Handle completion of a transfer (completion might be an error condition).
1649 * This will invoke the user-supplied callback function, which may end up
1650 * freeing the transfer. Therefore you cannot use the transfer structure
1651 * after calling this function, and you should free all backend-specific
1652 * data before calling it.
1653 * Do not call this function with the usbi_transfer lock held. User-specified
1654 * callback functions may attempt to directly resubmit the transfer, which
1655 * will attempt to take the lock. */
1656 int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1657 enum libusb_transfer_status status)
1659 struct libusb_transfer *transfer =
1660 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1661 struct libusb_device_handle *dev_handle = transfer->dev_handle;
1665 r = remove_from_flying_list(itransfer);
1667 usbi_err(ITRANSFER_CTX(itransfer), "failed to set timer for next timeout, errno=%d", errno);
1669 usbi_mutex_lock(&itransfer->lock);
1670 itransfer->state_flags &= ~USBI_TRANSFER_IN_FLIGHT;
1671 usbi_mutex_unlock(&itransfer->lock);
1673 if (status == LIBUSB_TRANSFER_COMPLETED
1674 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1675 int rqlen = transfer->length;
1676 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1677 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1678 if (rqlen != itransfer->transferred) {
1679 usbi_dbg("interpreting short transfer as error");
1680 status = LIBUSB_TRANSFER_ERROR;
1684 flags = transfer->flags;
1685 transfer->status = status;
1686 transfer->actual_length = itransfer->transferred;
1687 usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
1688 if (transfer->callback)
1689 transfer->callback(transfer);
1690 /* transfer might have been freed by the above call, do not use from
1692 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1693 libusb_free_transfer(transfer);
1694 libusb_unref_device(dev_handle->dev);
1698 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1699 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1700 * transfers exist here.
1701 * Do not call this function with the usbi_transfer lock held. User-specified
1702 * callback functions may attempt to directly resubmit the transfer, which
1703 * will attempt to take the lock. */
1704 int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
1706 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1709 usbi_mutex_lock(&ctx->flying_transfers_lock);
1710 timed_out = transfer->timeout_flags & USBI_TRANSFER_TIMED_OUT;
1711 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1713 /* if the URB was cancelled due to timeout, report timeout to the user */
1715 usbi_dbg("detected timeout cancellation");
1716 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
1719 /* otherwise its a normal async cancel */
1720 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
1723 /* Add a completed transfer to the completed_transfers list of the
1724 * context and signal the event. The backend's handle_transfer_completion()
1725 * function will be called the next time an event handler runs. */
1726 void usbi_signal_transfer_completion(struct usbi_transfer *transfer)
1728 libusb_device_handle *dev_handle = USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->dev_handle;
1731 struct libusb_context *ctx = HANDLE_CTX(dev_handle);
1734 usbi_mutex_lock(&ctx->event_data_lock);
1735 pending_events = usbi_pending_events(ctx);
1736 list_add_tail(&transfer->completed_list, &ctx->completed_transfers);
1737 if (!pending_events)
1738 usbi_signal_event(ctx);
1739 usbi_mutex_unlock(&ctx->event_data_lock);
1743 /** \ingroup libusb_poll
1744 * Attempt to acquire the event handling lock. This lock is used to ensure that
1745 * only one thread is monitoring libusb event sources at any one time.
1747 * You only need to use this lock if you are developing an application
1748 * which calls poll() or select() on libusb's file descriptors directly.
1749 * If you stick to libusb's event handling loop functions (e.g.
1750 * libusb_handle_events()) then you do not need to be concerned with this
1753 * While holding this lock, you are trusted to actually be handling events.
1754 * If you are no longer handling events, you must call libusb_unlock_events()
1755 * as soon as possible.
1757 * \param ctx the context to operate on, or NULL for the default context
1758 * \returns 0 if the lock was obtained successfully
1759 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1760 * \ref libusb_mtasync
1762 int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
1766 USBI_GET_CONTEXT(ctx);
1768 /* is someone else waiting to close a device? if so, don't let this thread
1769 * start event handling */
1770 usbi_mutex_lock(&ctx->event_data_lock);
1771 ru = ctx->device_close;
1772 usbi_mutex_unlock(&ctx->event_data_lock);
1774 usbi_dbg("someone else is closing a device");
1778 r = usbi_mutex_trylock(&ctx->events_lock);
1782 ctx->event_handler_active = 1;
1786 /** \ingroup libusb_poll
1787 * Acquire the event handling lock, blocking until successful acquisition if
1788 * it is contended. This lock is used to ensure that only one thread is
1789 * monitoring libusb event sources at any one time.
1791 * You only need to use this lock if you are developing an application
1792 * which calls poll() or select() on libusb's file descriptors directly.
1793 * If you stick to libusb's event handling loop functions (e.g.
1794 * libusb_handle_events()) then you do not need to be concerned with this
1797 * While holding this lock, you are trusted to actually be handling events.
1798 * If you are no longer handling events, you must call libusb_unlock_events()
1799 * as soon as possible.
1801 * \param ctx the context to operate on, or NULL for the default context
1802 * \ref libusb_mtasync
1804 void API_EXPORTED libusb_lock_events(libusb_context *ctx)
1806 USBI_GET_CONTEXT(ctx);
1807 usbi_mutex_lock(&ctx->events_lock);
1808 ctx->event_handler_active = 1;
1811 /** \ingroup libusb_poll
1812 * Release the lock previously acquired with libusb_try_lock_events() or
1813 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1814 * on libusb_wait_for_event().
1816 * \param ctx the context to operate on, or NULL for the default context
1817 * \ref libusb_mtasync
1819 void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
1821 USBI_GET_CONTEXT(ctx);
1822 ctx->event_handler_active = 0;
1823 usbi_mutex_unlock(&ctx->events_lock);
1825 /* FIXME: perhaps we should be a bit more efficient by not broadcasting
1826 * the availability of the events lock when we are modifying pollfds
1827 * (check ctx->device_close)? */
1828 usbi_mutex_lock(&ctx->event_waiters_lock);
1829 usbi_cond_broadcast(&ctx->event_waiters_cond);
1830 usbi_mutex_unlock(&ctx->event_waiters_lock);
1833 /** \ingroup libusb_poll
1834 * Determine if it is still OK for this thread to be doing event handling.
1836 * Sometimes, libusb needs to temporarily pause all event handlers, and this
1837 * is the function you should use before polling file descriptors to see if
1840 * If this function instructs your thread to give up the events lock, you
1841 * should just continue the usual logic that is documented in \ref libusb_mtasync.
1842 * On the next iteration, your thread will fail to obtain the events lock,
1843 * and will hence become an event waiter.
1845 * This function should be called while the events lock is held: you don't
1846 * need to worry about the results of this function if your thread is not
1847 * the current event handler.
1849 * \param ctx the context to operate on, or NULL for the default context
1850 * \returns 1 if event handling can start or continue
1851 * \returns 0 if this thread must give up the events lock
1852 * \ref fullstory "Multi-threaded I/O: the full story"
1854 int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
1857 USBI_GET_CONTEXT(ctx);
1859 /* is someone else waiting to close a device? if so, don't let this thread
1860 * continue event handling */
1861 usbi_mutex_lock(&ctx->event_data_lock);
1862 r = ctx->device_close;
1863 usbi_mutex_unlock(&ctx->event_data_lock);
1865 usbi_dbg("someone else is closing a device");
1873 /** \ingroup libusb_poll
1874 * Determine if an active thread is handling events (i.e. if anyone is holding
1875 * the event handling lock).
1877 * \param ctx the context to operate on, or NULL for the default context
1878 * \returns 1 if a thread is handling events
1879 * \returns 0 if there are no threads currently handling events
1880 * \ref libusb_mtasync
1882 int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
1885 USBI_GET_CONTEXT(ctx);
1887 /* is someone else waiting to close a device? if so, don't let this thread
1888 * start event handling -- indicate that event handling is happening */
1889 usbi_mutex_lock(&ctx->event_data_lock);
1890 r = ctx->device_close;
1891 usbi_mutex_unlock(&ctx->event_data_lock);
1893 usbi_dbg("someone else is closing a device");
1897 return ctx->event_handler_active;
1900 /** \ingroup libusb_poll
1901 * Interrupt any active thread that is handling events. This is mainly useful
1902 * for interrupting a dedicated event handling thread when an application
1903 * wishes to call libusb_exit().
1905 * Since version 1.0.21, \ref LIBUSB_API_VERSION >= 0x01000105
1907 * \param ctx the context to operate on, or NULL for the default context
1908 * \ref libusb_mtasync
1910 void API_EXPORTED libusb_interrupt_event_handler(libusb_context *ctx)
1913 USBI_GET_CONTEXT(ctx);
1916 usbi_mutex_lock(&ctx->event_data_lock);
1918 pending_events = usbi_pending_events(ctx);
1919 ctx->event_flags |= USBI_EVENT_USER_INTERRUPT;
1920 if (!pending_events)
1921 usbi_signal_event(ctx);
1923 usbi_mutex_unlock(&ctx->event_data_lock);
1926 /** \ingroup libusb_poll
1927 * Acquire the event waiters lock. This lock is designed to be obtained under
1928 * the situation where you want to be aware when events are completed, but
1929 * some other thread is event handling so calling libusb_handle_events() is not
1932 * You then obtain this lock, re-check that another thread is still handling
1933 * events, then call libusb_wait_for_event().
1935 * You only need to use this lock if you are developing an application
1936 * which calls poll() or select() on libusb's file descriptors directly,
1937 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1938 * If you stick to libusb's event handling loop functions (e.g.
1939 * libusb_handle_events()) then you do not need to be concerned with this
1942 * \param ctx the context to operate on, or NULL for the default context
1943 * \ref libusb_mtasync
1945 void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
1947 USBI_GET_CONTEXT(ctx);
1948 usbi_mutex_lock(&ctx->event_waiters_lock);
1951 /** \ingroup libusb_poll
1952 * Release the event waiters lock.
1953 * \param ctx the context to operate on, or NULL for the default context
1954 * \ref libusb_mtasync
1956 void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
1958 USBI_GET_CONTEXT(ctx);
1959 usbi_mutex_unlock(&ctx->event_waiters_lock);
1962 /** \ingroup libusb_poll
1963 * Wait for another thread to signal completion of an event. Must be called
1964 * with the event waiters lock held, see libusb_lock_event_waiters().
1966 * This function will block until any of the following conditions are met:
1967 * -# The timeout expires
1968 * -# A transfer completes
1969 * -# A thread releases the event handling lock through libusb_unlock_events()
1971 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1972 * the callback for the transfer has completed. Condition 3 is important
1973 * because it means that the thread that was previously handling events is no
1974 * longer doing so, so if any events are to complete, another thread needs to
1975 * step up and start event handling.
1977 * This function releases the event waiters lock before putting your thread
1978 * to sleep, and reacquires the lock as it is being woken up.
1980 * \param ctx the context to operate on, or NULL for the default context
1981 * \param tv maximum timeout for this blocking function. A NULL value
1982 * indicates unlimited timeout.
1983 * \returns 0 after a transfer completes or another thread stops event handling
1984 * \returns 1 if the timeout expired
1985 * \ref libusb_mtasync
1987 int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
1991 USBI_GET_CONTEXT(ctx);
1993 usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
1997 r = usbi_cond_timedwait(&ctx->event_waiters_cond,
1998 &ctx->event_waiters_lock, tv);
2003 return (r == ETIMEDOUT);
2006 static void handle_timeout(struct usbi_transfer *itransfer)
2008 struct libusb_transfer *transfer =
2009 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
2012 itransfer->timeout_flags |= USBI_TRANSFER_TIMEOUT_HANDLED;
2013 r = libusb_cancel_transfer(transfer);
2014 if (r == LIBUSB_SUCCESS)
2015 itransfer->timeout_flags |= USBI_TRANSFER_TIMED_OUT;
2017 usbi_warn(TRANSFER_CTX(transfer),
2018 "async cancel failed %d errno=%d", r, errno);
2021 static int handle_timeouts_locked(struct libusb_context *ctx)
2024 struct timespec systime_ts;
2025 struct timeval systime;
2026 struct usbi_transfer *transfer;
2028 if (list_empty(&ctx->flying_transfers))
2031 /* get current time */
2032 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
2036 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
2038 /* iterate through flying transfers list, finding all transfers that
2039 * have expired timeouts */
2040 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2041 struct timeval *cur_tv = &transfer->timeout;
2043 /* if we've reached transfers of infinite timeout, we're all done */
2044 if (!timerisset(cur_tv))
2047 /* ignore timeouts we've already handled */
2048 if (transfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2051 /* if transfer has non-expired timeout, nothing more to do */
2052 if ((cur_tv->tv_sec > systime.tv_sec) ||
2053 (cur_tv->tv_sec == systime.tv_sec &&
2054 cur_tv->tv_usec > systime.tv_usec))
2057 /* otherwise, we've got an expired timeout to handle */
2058 handle_timeout(transfer);
2063 static int handle_timeouts(struct libusb_context *ctx)
2066 USBI_GET_CONTEXT(ctx);
2067 usbi_mutex_lock(&ctx->flying_transfers_lock);
2068 r = handle_timeouts_locked(ctx);
2069 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2073 #ifdef USBI_TIMERFD_AVAILABLE
2074 static int handle_timerfd_trigger(struct libusb_context *ctx)
2078 usbi_mutex_lock(&ctx->flying_transfers_lock);
2080 /* process the timeout that just happened */
2081 r = handle_timeouts_locked(ctx);
2085 /* arm for next timeout*/
2086 r = arm_timerfd_for_next_timeout(ctx);
2089 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2094 /* do the actual event handling. assumes that no other thread is concurrently
2095 * doing the same thing. */
2096 static int handle_events(struct libusb_context *ctx, struct timeval *tv)
2099 struct usbi_pollfd *ipollfd;
2100 POLL_NFDS_TYPE nfds = 0;
2101 POLL_NFDS_TYPE internal_nfds;
2102 struct pollfd *fds = NULL;
2105 /* prevent attempts to recursively handle events (e.g. calling into
2106 * libusb_handle_events() from within a hotplug or transfer callback) */
2107 usbi_mutex_lock(&ctx->event_data_lock);
2109 if (usbi_handling_events(ctx))
2110 r = LIBUSB_ERROR_BUSY;
2112 usbi_start_event_handling(ctx);
2113 usbi_mutex_unlock(&ctx->event_data_lock);
2118 /* there are certain fds that libusb uses internally, currently:
2123 * the backend will never need to attempt to handle events on these fds, so
2124 * we determine how many fds are in use internally for this context and when
2125 * handle_events() is called in the backend, the pollfd list and count will
2126 * be adjusted to skip over these internal fds */
2127 if (usbi_using_timerfd(ctx))
2132 /* only reallocate the poll fds when the list of poll fds has been modified
2133 * since the last poll, otherwise reuse them to save the additional overhead */
2134 usbi_mutex_lock(&ctx->event_data_lock);
2135 /* clean up removed poll fds */
2136 cleanup_removed_pollfds(ctx);
2137 if (ctx->event_flags & USBI_EVENT_POLLFDS_MODIFIED) {
2140 usbi_dbg("poll fds modified, reallocating");
2143 ctx->pollfds = NULL;
2145 /* sanity check - it is invalid for a context to have fewer than the
2146 * required internal fds (memory corruption?) */
2147 assert(ctx->pollfds_cnt >= internal_nfds);
2149 ctx->pollfds = calloc(ctx->pollfds_cnt, sizeof(*ctx->pollfds));
2150 if (!ctx->pollfds) {
2151 usbi_mutex_unlock(&ctx->event_data_lock);
2152 r = LIBUSB_ERROR_NO_MEM;
2156 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd) {
2157 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
2158 ctx->pollfds[i].fd = pollfd->fd;
2159 ctx->pollfds[i].events = pollfd->events;
2163 /* reset the flag now that we have the updated list */
2164 ctx->event_flags &= ~USBI_EVENT_POLLFDS_MODIFIED;
2166 /* if no further pending events, clear the event pipe so that we do
2167 * not immediately return from poll */
2168 if (!usbi_pending_events(ctx))
2169 usbi_clear_event(ctx);
2172 nfds = ctx->pollfds_cnt;
2173 usbi_mutex_unlock(&ctx->event_data_lock);
2175 timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000);
2177 /* round up to next millisecond */
2178 if (tv->tv_usec % 1000)
2181 usbi_dbg("poll() %d fds with timeout in %dms", (int)nfds, timeout_ms);
2182 r = usbi_poll(fds, nfds, timeout_ms);
2183 usbi_dbg("poll() returned %d", r);
2185 r = handle_timeouts(ctx);
2187 } else if (r == -1 && errno == EINTR) {
2188 r = LIBUSB_ERROR_INTERRUPTED;
2191 usbi_err(ctx, "poll failed %d err=%d", r, errno);
2192 r = LIBUSB_ERROR_IO;
2196 /* fds[0] is always the event pipe */
2197 if (fds[0].revents) {
2198 struct list_head hotplug_msgs;
2199 struct usbi_transfer *itransfer;
2200 int hotplug_cb_deregistered = 0;
2203 list_init(&hotplug_msgs);
2205 usbi_dbg("caught a fish on the event pipe");
2207 /* take the the event data lock while processing events */
2208 usbi_mutex_lock(&ctx->event_data_lock);
2210 /* check if someone added a new poll fd */
2211 if (ctx->event_flags & USBI_EVENT_POLLFDS_MODIFIED)
2212 usbi_dbg("someone updated the poll fds");
2214 if (ctx->event_flags & USBI_EVENT_USER_INTERRUPT) {
2215 usbi_dbg("someone purposely interrupted");
2216 ctx->event_flags &= ~USBI_EVENT_USER_INTERRUPT;
2219 if (ctx->event_flags & USBI_EVENT_HOTPLUG_CB_DEREGISTERED) {
2220 usbi_dbg("someone unregistered a hotplug cb");
2221 ctx->event_flags &= ~USBI_EVENT_HOTPLUG_CB_DEREGISTERED;
2222 hotplug_cb_deregistered = 1;
2225 /* check if someone is closing a device */
2226 if (ctx->device_close)
2227 usbi_dbg("someone is closing a device");
2229 /* check for any pending hotplug messages */
2230 if (!list_empty(&ctx->hotplug_msgs)) {
2231 usbi_dbg("hotplug message received");
2232 list_cut(&hotplug_msgs, &ctx->hotplug_msgs);
2235 /* complete any pending transfers */
2236 while (ret == 0 && !list_empty(&ctx->completed_transfers)) {
2237 itransfer = list_first_entry(&ctx->completed_transfers, struct usbi_transfer, completed_list);
2238 list_del(&itransfer->completed_list);
2239 usbi_mutex_unlock(&ctx->event_data_lock);
2240 ret = usbi_backend.handle_transfer_completion(itransfer);
2242 usbi_err(ctx, "backend handle_transfer_completion failed with error %d", ret);
2243 usbi_mutex_lock(&ctx->event_data_lock);
2246 /* if no further pending events, clear the event pipe */
2247 if (!usbi_pending_events(ctx))
2248 usbi_clear_event(ctx);
2250 usbi_mutex_unlock(&ctx->event_data_lock);
2252 if (hotplug_cb_deregistered)
2253 usbi_hotplug_deregister(ctx, 0);
2255 /* process the hotplug messages, if any */
2256 while (!list_empty(&hotplug_msgs)) {
2257 struct libusb_hotplug_message *message =
2258 list_first_entry(&hotplug_msgs, struct libusb_hotplug_message, list);
2260 usbi_hotplug_match(ctx, message->device, message->event);
2262 /* the device left, dereference the device */
2263 if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == message->event)
2264 libusb_unref_device(message->device);
2266 list_del(&message->list);
2271 /* return error code */
2280 #ifdef USBI_TIMERFD_AVAILABLE
2281 /* on timerfd configurations, fds[1] is the timerfd */
2282 if (usbi_using_timerfd(ctx) && fds[1].revents) {
2283 /* timerfd indicates that a timeout has expired */
2285 usbi_dbg("timerfd triggered");
2287 ret = handle_timerfd_trigger(ctx);
2289 /* return error code */
2299 list_for_each_entry(ipollfd, &ctx->removed_ipollfds, list, struct usbi_pollfd) {
2302 for (n = internal_nfds ; n < nfds ; n++) {
2303 if (ipollfd->pollfd.fd == fds[n].fd) {
2304 /* pollfd was removed between the creation of the fd
2305 * array and here. remove any triggered revent as
2306 * it is no longer relevant */
2307 usbi_dbg("pollfd %d was removed. ignoring raised events",
2315 r = usbi_backend.handle_events(ctx, fds + internal_nfds, nfds - internal_nfds, r);
2317 usbi_err(ctx, "backend handle_events failed with error %d", r);
2320 usbi_end_event_handling(ctx);
2324 /* returns the smallest of:
2325 * 1. timeout of next URB
2326 * 2. user-supplied timeout
2327 * returns 1 if there is an already-expired timeout, otherwise returns 0
2330 static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
2331 struct timeval *out)
2333 struct timeval timeout;
2334 int r = libusb_get_next_timeout(ctx, &timeout);
2336 /* timeout already expired? */
2337 if (!timerisset(&timeout))
2340 /* choose the smallest of next URB timeout or user specified timeout */
2341 if (timercmp(&timeout, tv, <))
2351 /** \ingroup libusb_poll
2352 * Handle any pending events.
2354 * libusb determines "pending events" by checking if any timeouts have expired
2355 * and by checking the set of file descriptors for activity.
2357 * If a zero timeval is passed, this function will handle any already-pending
2358 * events and then immediately return in non-blocking style.
2360 * If a non-zero timeval is passed and no events are currently pending, this
2361 * function will block waiting for events to handle up until the specified
2362 * timeout. If an event arrives or a signal is raised, this function will
2365 * If the parameter completed is not NULL then <em>after obtaining the event
2366 * handling lock</em> this function will return immediately if the integer
2367 * pointed to is not 0. This allows for race free waiting for the completion
2368 * of a specific transfer.
2370 * \param ctx the context to operate on, or NULL for the default context
2371 * \param tv the maximum time to block waiting for events, or an all zero
2372 * timeval struct for non-blocking mode
2373 * \param completed pointer to completion integer to check, or NULL
2374 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2375 * \ref libusb_mtasync
2377 int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
2378 struct timeval *tv, int *completed)
2381 struct timeval poll_timeout;
2383 USBI_GET_CONTEXT(ctx);
2384 r = get_next_timeout(ctx, tv, &poll_timeout);
2386 /* timeout already expired */
2387 return handle_timeouts(ctx);
2391 if (libusb_try_lock_events(ctx) == 0) {
2392 if (completed == NULL || !*completed) {
2393 /* we obtained the event lock: do our own event handling */
2394 usbi_dbg("doing our own event handling");
2395 r = handle_events(ctx, &poll_timeout);
2397 libusb_unlock_events(ctx);
2401 /* another thread is doing event handling. wait for thread events that
2402 * notify event completion. */
2403 libusb_lock_event_waiters(ctx);
2405 if (completed && *completed)
2408 if (!libusb_event_handler_active(ctx)) {
2409 /* we hit a race: whoever was event handling earlier finished in the
2410 * time it took us to reach this point. try the cycle again. */
2411 libusb_unlock_event_waiters(ctx);
2412 usbi_dbg("event handler was active but went away, retrying");
2416 usbi_dbg("another thread is doing event handling");
2417 r = libusb_wait_for_event(ctx, &poll_timeout);
2420 libusb_unlock_event_waiters(ctx);
2425 return handle_timeouts(ctx);
2430 /** \ingroup libusb_poll
2431 * Handle any pending events
2433 * Like libusb_handle_events_timeout_completed(), but without the completed
2434 * parameter, calling this function is equivalent to calling
2435 * libusb_handle_events_timeout_completed() with a NULL completed parameter.
2437 * This function is kept primarily for backwards compatibility.
2438 * All new code should call libusb_handle_events_completed() or
2439 * libusb_handle_events_timeout_completed() to avoid race conditions.
2441 * \param ctx the context to operate on, or NULL for the default context
2442 * \param tv the maximum time to block waiting for events, or an all zero
2443 * timeval struct for non-blocking mode
2444 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2446 int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
2449 return libusb_handle_events_timeout_completed(ctx, tv, NULL);
2452 /** \ingroup libusb_poll
2453 * Handle any pending events in blocking mode. There is currently a timeout
2454 * hardcoded at 60 seconds but we plan to make it unlimited in future. For
2455 * finer control over whether this function is blocking or non-blocking, or
2456 * for control over the timeout, use libusb_handle_events_timeout_completed()
2459 * This function is kept primarily for backwards compatibility.
2460 * All new code should call libusb_handle_events_completed() or
2461 * libusb_handle_events_timeout_completed() to avoid race conditions.
2463 * \param ctx the context to operate on, or NULL for the default context
2464 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2466 int API_EXPORTED libusb_handle_events(libusb_context *ctx)
2471 return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
2474 /** \ingroup libusb_poll
2475 * Handle any pending events in blocking mode.
2477 * Like libusb_handle_events(), with the addition of a completed parameter
2478 * to allow for race free waiting for the completion of a specific transfer.
2480 * See libusb_handle_events_timeout_completed() for details on the completed
2483 * \param ctx the context to operate on, or NULL for the default context
2484 * \param completed pointer to completion integer to check, or NULL
2485 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2486 * \ref libusb_mtasync
2488 int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
2494 return libusb_handle_events_timeout_completed(ctx, &tv, completed);
2497 /** \ingroup libusb_poll
2498 * Handle any pending events by polling file descriptors, without checking if
2499 * any other threads are already doing so. Must be called with the event lock
2500 * held, see libusb_lock_events().
2502 * This function is designed to be called under the situation where you have
2503 * taken the event lock and are calling poll()/select() directly on libusb's
2504 * file descriptors (as opposed to using libusb_handle_events() or similar).
2505 * You detect events on libusb's descriptors, so you then call this function
2506 * with a zero timeout value (while still holding the event lock).
2508 * \param ctx the context to operate on, or NULL for the default context
2509 * \param tv the maximum time to block waiting for events, or zero for
2511 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2512 * \ref libusb_mtasync
2514 int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
2518 struct timeval poll_timeout;
2520 USBI_GET_CONTEXT(ctx);
2521 r = get_next_timeout(ctx, tv, &poll_timeout);
2523 /* timeout already expired */
2524 return handle_timeouts(ctx);
2527 return handle_events(ctx, &poll_timeout);
2530 /** \ingroup libusb_poll
2531 * Determines whether your application must apply special timing considerations
2532 * when monitoring libusb's file descriptors.
2534 * This function is only useful for applications which retrieve and poll
2535 * libusb's file descriptors in their own main loop (\ref libusb_pollmain).
2537 * Ordinarily, libusb's event handler needs to be called into at specific
2538 * moments in time (in addition to times when there is activity on the file
2539 * descriptor set). The usual approach is to use libusb_get_next_timeout()
2540 * to learn about when the next timeout occurs, and to adjust your
2541 * poll()/select() timeout accordingly so that you can make a call into the
2542 * library at that time.
2544 * Some platforms supported by libusb do not come with this baggage - any
2545 * events relevant to timing will be represented by activity on the file
2546 * descriptor set, and libusb_get_next_timeout() will always return 0.
2547 * This function allows you to detect whether you are running on such a
2552 * \param ctx the context to operate on, or NULL for the default context
2553 * \returns 0 if you must call into libusb at times determined by
2554 * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
2555 * or through regular activity on the file descriptors.
2556 * \ref libusb_pollmain "Polling libusb file descriptors for event handling"
2558 int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
2560 #if defined(USBI_TIMERFD_AVAILABLE)
2561 USBI_GET_CONTEXT(ctx);
2562 return usbi_using_timerfd(ctx);
2569 /** \ingroup libusb_poll
2570 * Determine the next internal timeout that libusb needs to handle. You only
2571 * need to use this function if you are calling poll() or select() or similar
2572 * on libusb's file descriptors yourself - you do not need to use it if you
2573 * are calling libusb_handle_events() or a variant directly.
2575 * You should call this function in your main loop in order to determine how
2576 * long to wait for select() or poll() to return results. libusb needs to be
2577 * called into at this timeout, so you should use it as an upper bound on
2578 * your select() or poll() call.
2580 * When the timeout has expired, call into libusb_handle_events_timeout()
2581 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
2583 * This function may return 1 (success) and an all-zero timeval. If this is
2584 * the case, it indicates that libusb has a timeout that has already expired
2585 * so you should call libusb_handle_events_timeout() or similar immediately.
2586 * A return code of 0 indicates that there are no pending timeouts.
2588 * On some platforms, this function will always returns 0 (no pending
2589 * timeouts). See \ref polltime.
2591 * \param ctx the context to operate on, or NULL for the default context
2592 * \param tv output location for a relative time against the current
2593 * clock in which libusb must be called into in order to process timeout events
2594 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
2595 * or LIBUSB_ERROR_OTHER on failure
2597 int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
2600 struct usbi_transfer *transfer;
2601 struct timespec cur_ts;
2602 struct timeval cur_tv;
2603 struct timeval next_timeout = { 0, 0 };
2606 USBI_GET_CONTEXT(ctx);
2607 if (usbi_using_timerfd(ctx))
2610 usbi_mutex_lock(&ctx->flying_transfers_lock);
2611 if (list_empty(&ctx->flying_transfers)) {
2612 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2613 usbi_dbg("no URBs, no timeout!");
2617 /* find next transfer which hasn't already been processed as timed out */
2618 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2619 if (transfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2622 /* if we've reached transfers of infinte timeout, we're done looking */
2623 if (!timerisset(&transfer->timeout))
2626 next_timeout = transfer->timeout;
2629 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2631 if (!timerisset(&next_timeout)) {
2632 usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
2636 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
2638 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2641 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
2643 if (!timercmp(&cur_tv, &next_timeout, <)) {
2644 usbi_dbg("first timeout already expired");
2647 timersub(&next_timeout, &cur_tv, tv);
2648 usbi_dbg("next timeout in %ld.%06lds", (long)tv->tv_sec, (long)tv->tv_usec);
2654 /** \ingroup libusb_poll
2655 * Register notification functions for file descriptor additions/removals.
2656 * These functions will be invoked for every new or removed file descriptor
2657 * that libusb uses as an event source.
2659 * To remove notifiers, pass NULL values for the function pointers.
2661 * Note that file descriptors may have been added even before you register
2662 * these notifiers (e.g. at libusb_init() time).
2664 * Additionally, note that the removal notifier may be called during
2665 * libusb_exit() (e.g. when it is closing file descriptors that were opened
2666 * and added to the poll set at libusb_init() time). If you don't want this,
2667 * remove the notifiers immediately before calling libusb_exit().
2669 * \param ctx the context to operate on, or NULL for the default context
2670 * \param added_cb pointer to function for addition notifications
2671 * \param removed_cb pointer to function for removal notifications
2672 * \param user_data User data to be passed back to callbacks (useful for
2673 * passing context information)
2675 void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
2676 libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
2679 USBI_GET_CONTEXT(ctx);
2680 ctx->fd_added_cb = added_cb;
2681 ctx->fd_removed_cb = removed_cb;
2682 ctx->fd_cb_user_data = user_data;
2686 * Interrupt the iteration of the event handling thread, so that it picks
2687 * up the fd change. Callers of this function must hold the event_data_lock.
2689 static void usbi_fd_notification(struct libusb_context *ctx)
2693 /* Record that there is a new poll fd.
2694 * Only signal an event if there are no prior pending events. */
2695 pending_events = usbi_pending_events(ctx);
2696 ctx->event_flags |= USBI_EVENT_POLLFDS_MODIFIED;
2697 if (!pending_events)
2698 usbi_signal_event(ctx);
2701 /* Add a file descriptor to the list of file descriptors to be monitored.
2702 * events should be specified as a bitmask of events passed to poll(), e.g.
2703 * POLLIN and/or POLLOUT. */
2704 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
2706 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
2708 return LIBUSB_ERROR_NO_MEM;
2710 usbi_dbg("add fd %d events %d", fd, events);
2711 ipollfd->pollfd.fd = fd;
2712 ipollfd->pollfd.events = events;
2713 usbi_mutex_lock(&ctx->event_data_lock);
2714 list_add_tail(&ipollfd->list, &ctx->ipollfds);
2716 usbi_fd_notification(ctx);
2717 usbi_mutex_unlock(&ctx->event_data_lock);
2719 if (ctx->fd_added_cb)
2720 ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
2724 /* Remove a file descriptor from the list of file descriptors to be polled. */
2725 void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
2727 struct usbi_pollfd *ipollfd;
2730 usbi_dbg("remove fd %d", fd);
2731 usbi_mutex_lock(&ctx->event_data_lock);
2732 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd)
2733 if (ipollfd->pollfd.fd == fd) {
2739 usbi_dbg("couldn't find fd %d to remove", fd);
2740 usbi_mutex_unlock(&ctx->event_data_lock);
2744 list_del(&ipollfd->list);
2745 list_add_tail(&ipollfd->list, &ctx->removed_ipollfds);
2747 usbi_fd_notification(ctx);
2748 usbi_mutex_unlock(&ctx->event_data_lock);
2750 if (ctx->fd_removed_cb)
2751 ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
2754 /** \ingroup libusb_poll
2755 * Retrieve a list of file descriptors that should be polled by your main loop
2756 * as libusb event sources.
2758 * The returned list is NULL-terminated and should be freed with libusb_free_pollfds()
2759 * when done. The actual list contents must not be touched.
2761 * As file descriptors are a Unix-specific concept, this function is not
2762 * available on Windows and will always return NULL.
2764 * \param ctx the context to operate on, or NULL for the default context
2765 * \returns a NULL-terminated list of libusb_pollfd structures
2766 * \returns NULL on error
2767 * \returns NULL on platforms where the functionality is not available
2770 const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
2771 libusb_context *ctx)
2774 struct libusb_pollfd **ret = NULL;
2775 struct usbi_pollfd *ipollfd;
2777 USBI_GET_CONTEXT(ctx);
2779 usbi_mutex_lock(&ctx->event_data_lock);
2781 ret = calloc(ctx->pollfds_cnt + 1, sizeof(struct libusb_pollfd *));
2785 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd)
2786 ret[i++] = (struct libusb_pollfd *) ipollfd;
2787 ret[ctx->pollfds_cnt] = NULL;
2790 usbi_mutex_unlock(&ctx->event_data_lock);
2791 return (const struct libusb_pollfd **) ret;
2793 usbi_err(ctx, "external polling of libusb's internal descriptors "\
2794 "is not yet supported on Windows platforms");
2799 /** \ingroup libusb_poll
2800 * Free a list of libusb_pollfd structures. This should be called for all
2801 * pollfd lists allocated with libusb_get_pollfds().
2803 * Since version 1.0.20, \ref LIBUSB_API_VERSION >= 0x01000104
2805 * It is legal to call this function with a NULL pollfd list. In this case,
2806 * the function will simply do nothing.
2808 * \param pollfds the list of libusb_pollfd structures to free
2810 void API_EXPORTED libusb_free_pollfds(const struct libusb_pollfd **pollfds)
2812 free((void *)pollfds);
2815 /* Backends may call this from handle_events to report disconnection of a
2816 * device. This function ensures transfers get cancelled appropriately.
2817 * Callers of this function must hold the events_lock.
2819 void usbi_handle_disconnect(struct libusb_device_handle *dev_handle)
2821 struct usbi_transfer *cur;
2822 struct usbi_transfer *to_cancel;
2824 usbi_dbg("device %d.%d",
2825 dev_handle->dev->bus_number, dev_handle->dev->device_address);
2827 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
2830 * when we find a transfer for this device on the list, there are two
2831 * possible scenarios:
2832 * 1. the transfer is currently in-flight, in which case we terminate the
2834 * 2. the transfer has been added to the flying transfer list by
2835 * libusb_submit_transfer, has failed to submit and
2836 * libusb_submit_transfer is waiting for us to release the
2837 * flying_transfers_lock to remove it, so we ignore it
2842 usbi_mutex_lock(&HANDLE_CTX(dev_handle)->flying_transfers_lock);
2843 list_for_each_entry(cur, &HANDLE_CTX(dev_handle)->flying_transfers, list, struct usbi_transfer)
2844 if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == dev_handle) {
2845 usbi_mutex_lock(&cur->lock);
2846 if (cur->state_flags & USBI_TRANSFER_IN_FLIGHT)
2848 usbi_mutex_unlock(&cur->lock);
2853 usbi_mutex_unlock(&HANDLE_CTX(dev_handle)->flying_transfers_lock);
2858 usbi_dbg("cancelling transfer %p from disconnect",
2859 USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel));
2861 usbi_mutex_lock(&to_cancel->lock);
2862 usbi_backend.clear_transfer_priv(to_cancel);
2863 usbi_mutex_unlock(&to_cancel->lock);
2864 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);