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
29 #include <sys/timerfd.h>
34 * \page libusb_io Synchronous and asynchronous device I/O
36 * \section io_intro Introduction
38 * If you're using libusb in your application, you're probably wanting to
39 * perform I/O with devices - you want to perform USB data transfers.
41 * libusb offers two separate interfaces for device I/O. This page aims to
42 * introduce the two in order to help you decide which one is more suitable
43 * for your application. You can also choose to use both interfaces in your
44 * application by considering each transfer on a case-by-case basis.
46 * Once you have read through the following discussion, you should consult the
47 * detailed API documentation pages for the details:
48 * - \ref libusb_syncio
49 * - \ref libusb_asyncio
51 * \section theory Transfers at a logical level
53 * At a logical level, USB transfers typically happen in two parts. For
54 * example, when reading data from a endpoint:
55 * -# A request for data is sent to the device
56 * -# Some time later, the incoming data is received by the host
58 * or when writing data to an endpoint:
60 * -# The data is sent to the device
61 * -# Some time later, the host receives acknowledgement from the device that
62 * the data has been transferred.
64 * There may be an indefinite delay between the two steps. Consider a
65 * fictional USB input device with a button that the user can press. In order
66 * to determine when the button is pressed, you would likely submit a request
67 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
68 * Data will arrive when the button is pressed by the user, which is
69 * potentially hours later.
71 * libusb offers both a synchronous and an asynchronous interface to performing
72 * USB transfers. The main difference is that the synchronous interface
73 * combines both steps indicated above into a single function call, whereas
74 * the asynchronous interface separates them.
76 * \section sync The synchronous interface
78 * The synchronous I/O interface allows you to perform a USB transfer with
79 * a single function call. When the function call returns, the transfer has
80 * completed and you can parse the results.
82 * If you have used the libusb-0.1 before, this I/O style will seem familar to
83 * you. libusb-0.1 only offered a synchronous interface.
85 * In our input device example, to read button presses you might write code
86 * in the following style:
88 unsigned char data[4];
90 int r = libusb_bulk_transfer(dev_handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
91 if (r == 0 && actual_length == sizeof(data)) {
92 // results of the transaction can now be found in the data buffer
93 // parse them here and report button press
99 * The main advantage of this model is simplicity: you did everything with
100 * a single simple function call.
102 * However, this interface has its limitations. Your application will sleep
103 * inside libusb_bulk_transfer() until the transaction has completed. If it
104 * takes the user 3 hours to press the button, your application will be
105 * sleeping for that long. Execution will be tied up inside the library -
106 * the entire thread will be useless for that duration.
108 * Another issue is that by tieing up the thread with that single transaction
109 * there is no possibility of performing I/O with multiple endpoints and/or
110 * multiple devices simultaneously, unless you resort to creating one thread
113 * Additionally, there is no opportunity to cancel the transfer after the
114 * request has been submitted.
116 * For details on how to use the synchronous API, see the
117 * \ref libusb_syncio "synchronous I/O API documentation" pages.
119 * \section async The asynchronous interface
121 * Asynchronous I/O is the most significant new feature in libusb-1.0.
122 * Although it is a more complex interface, it solves all the issues detailed
125 * Instead of providing which functions that block until the I/O has complete,
126 * libusb's asynchronous interface presents non-blocking functions which
127 * begin a transfer and then return immediately. Your application passes a
128 * callback function pointer to this non-blocking function, which libusb will
129 * call with the results of the transaction when it has completed.
131 * Transfers which have been submitted through the non-blocking functions
132 * can be cancelled with a separate function call.
134 * The non-blocking nature of this interface allows you to be simultaneously
135 * performing I/O to multiple endpoints on multiple devices, without having
138 * This added flexibility does come with some complications though:
139 * - In the interest of being a lightweight library, libusb does not create
140 * threads and can only operate when your application is calling into it. Your
141 * application must call into libusb from it's main loop when events are ready
142 * to be handled, or you must use some other scheme to allow libusb to
143 * undertake whatever work needs to be done.
144 * - libusb also needs to be called into at certain fixed points in time in
145 * order to accurately handle transfer timeouts.
146 * - Memory handling becomes more complex. You cannot use stack memory unless
147 * the function with that stack is guaranteed not to return until the transfer
148 * callback has finished executing.
149 * - You generally lose some linearity from your code flow because submitting
150 * the transfer request is done in a separate function from where the transfer
151 * results are handled. This becomes particularly obvious when you want to
152 * submit a second transfer based on the results of an earlier transfer.
154 * Internally, libusb's synchronous interface is expressed in terms of function
155 * calls to the asynchronous interface.
157 * For details on how to use the asynchronous API, see the
158 * \ref libusb_asyncio "asynchronous I/O API" documentation pages.
163 * \page libusb_packetoverflow Packets and overflows
165 * \section packets Packet abstraction
167 * The USB specifications describe how data is transmitted in packets, with
168 * constraints on packet size defined by endpoint descriptors. The host must
169 * not send data payloads larger than the endpoint's maximum packet size.
171 * libusb and the underlying OS abstract out the packet concept, allowing you
172 * to request transfers of any size. Internally, the request will be divided
173 * up into correctly-sized packets. You do not have to be concerned with
174 * packet sizes, but there is one exception when considering overflows.
176 * \section overflow Bulk/interrupt transfer overflows
178 * When requesting data on a bulk endpoint, libusb requires you to supply a
179 * buffer and the maximum number of bytes of data that libusb can put in that
180 * buffer. However, the size of the buffer is not communicated to the device -
181 * the device is just asked to send any amount of data.
183 * There is no problem if the device sends an amount of data that is less than
184 * or equal to the buffer size. libusb reports this condition to you through
185 * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
188 * Problems may occur if the device attempts to send more data than can fit in
189 * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
190 * other behaviour is largely undefined: actual_length may or may not be
191 * accurate, the chunk of data that can fit in the buffer (before overflow)
192 * may or may not have been transferred.
194 * Overflows are nasty, but can be avoided. Even though you were told to
195 * ignore packets above, think about the lower level details: each transfer is
196 * split into packets (typically small, with a maximum size of 512 bytes).
197 * Overflows can only happen if the final packet in an incoming data transfer
198 * is smaller than the actual packet that the device wants to transfer.
199 * Therefore, you will never see an overflow if your transfer buffer size is a
200 * multiple of the endpoint's packet size: the final packet will either
201 * fill up completely or will be only partially filled.
205 * @defgroup libusb_asyncio Asynchronous device I/O
207 * This page details libusb's asynchronous (non-blocking) API for USB device
208 * I/O. This interface is very powerful but is also quite complex - you will
209 * need to read this page carefully to understand the necessary considerations
210 * and issues surrounding use of this interface. Simplistic applications
211 * may wish to consider the \ref libusb_syncio "synchronous I/O API" instead.
213 * The asynchronous interface is built around the idea of separating transfer
214 * submission and handling of transfer completion (the synchronous model
215 * combines both of these into one). There may be a long delay between
216 * submission and completion, however the asynchronous submission function
217 * is non-blocking so will return control to your application during that
218 * potentially long delay.
220 * \section asyncabstraction Transfer abstraction
222 * For the asynchronous I/O, libusb implements the concept of a generic
223 * transfer entity for all types of I/O (control, bulk, interrupt,
224 * isochronous). The generic transfer object must be treated slightly
225 * differently depending on which type of I/O you are performing with it.
227 * This is represented by the public libusb_transfer structure type.
229 * \section asynctrf Asynchronous transfers
231 * We can view asynchronous I/O as a 5 step process:
232 * -# <b>Allocation</b>: allocate a libusb_transfer
233 * -# <b>Filling</b>: populate the libusb_transfer instance with information
234 * about the transfer you wish to perform
235 * -# <b>Submission</b>: ask libusb to submit the transfer
236 * -# <b>Completion handling</b>: examine transfer results in the
237 * libusb_transfer structure
238 * -# <b>Deallocation</b>: clean up resources
241 * \subsection asyncalloc Allocation
243 * This step involves allocating memory for a USB transfer. This is the
244 * generic transfer object mentioned above. At this stage, the transfer
245 * is "blank" with no details about what type of I/O it will be used for.
247 * Allocation is done with the libusb_alloc_transfer() function. You must use
248 * this function rather than allocating your own transfers.
250 * \subsection asyncfill Filling
252 * This step is where you take a previously allocated transfer and fill it
253 * with information to determine the message type and direction, data buffer,
254 * callback function, etc.
256 * You can either fill the required fields yourself or you can use the
257 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
258 * and libusb_fill_interrupt_transfer().
260 * \subsection asyncsubmit Submission
262 * When you have allocated a transfer and filled it, you can submit it using
263 * libusb_submit_transfer(). This function returns immediately but can be
264 * regarded as firing off the I/O request in the background.
266 * \subsection asynccomplete Completion handling
268 * After a transfer has been submitted, one of four things can happen to it:
270 * - The transfer completes (i.e. some data was transferred)
271 * - The transfer has a timeout and the timeout expires before all data is
273 * - The transfer fails due to an error
274 * - The transfer is cancelled
276 * Each of these will cause the user-specified transfer callback function to
277 * be invoked. It is up to the callback function to determine which of the
278 * above actually happened and to act accordingly.
280 * The user-specified callback is passed a pointer to the libusb_transfer
281 * structure which was used to setup and submit the transfer. At completion
282 * time, libusb has populated this structure with results of the transfer:
283 * success or failure reason, number of bytes of data transferred, etc. See
284 * the libusb_transfer structure documentation for more information.
286 * <b>Important Note</b>: The user-specified callback is called from an event
287 * handling context. It is therefore important that no calls are made into
288 * libusb that will attempt to perform any event handling. Examples of such
289 * functions are any listed in the \ref libusb_syncio "synchronous API" and any of
290 * the blocking functions that retrieve \ref libusb_desc "USB descriptors".
292 * \subsection Deallocation
294 * When a transfer has completed (i.e. the callback function has been invoked),
295 * you are advised to free the transfer (unless you wish to resubmit it, see
296 * below). Transfers are deallocated with libusb_free_transfer().
298 * It is undefined behaviour to free a transfer which has not completed.
300 * \section asyncresubmit Resubmission
302 * You may be wondering why allocation, filling, and submission are all
303 * separated above where they could reasonably be combined into a single
306 * The reason for separation is to allow you to resubmit transfers without
307 * having to allocate new ones every time. This is especially useful for
308 * common situations dealing with interrupt endpoints - you allocate one
309 * transfer, fill and submit it, and when it returns with results you just
310 * resubmit it for the next interrupt.
312 * \section asynccancel Cancellation
314 * Another advantage of using the asynchronous interface is that you have
315 * the ability to cancel transfers which have not yet completed. This is
316 * done by calling the libusb_cancel_transfer() function.
318 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
319 * cancellation actually completes, the transfer's callback function will
320 * be invoked, and the callback function should check the transfer status to
321 * determine that it was cancelled.
323 * Freeing the transfer after it has been cancelled but before cancellation
324 * has completed will result in undefined behaviour.
326 * When a transfer is cancelled, some of the data may have been transferred.
327 * libusb will communicate this to you in the transfer callback. Do not assume
328 * that no data was transferred.
330 * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
332 * If your device does not have predictable transfer sizes (or it misbehaves),
333 * your application may submit a request for data on an IN endpoint which is
334 * smaller than the data that the device wishes to send. In some circumstances
335 * this will cause an overflow, which is a nasty condition to deal with. See
336 * the \ref libusb_packetoverflow page for discussion.
338 * \section asyncctrl Considerations for control transfers
340 * The <tt>libusb_transfer</tt> structure is generic and hence does not
341 * include specific fields for the control-specific setup packet structure.
343 * In order to perform a control transfer, you must place the 8-byte setup
344 * packet at the start of the data buffer. To simplify this, you could
345 * cast the buffer pointer to type struct libusb_control_setup, or you can
346 * use the helper function libusb_fill_control_setup().
348 * The wLength field placed in the setup packet must be the length you would
349 * expect to be sent in the setup packet: the length of the payload that
350 * follows (or the expected maximum number of bytes to receive). However,
351 * the length field of the libusb_transfer object must be the length of
352 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
353 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
355 * If you use the helper functions, this is simplified for you:
356 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
357 * data you are sending/requesting.
358 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
359 * request size as the wLength value (i.e. do not include the extra space you
360 * allocated for the control setup).
361 * -# If this is a host-to-device transfer, place the data to be transferred
362 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
363 * -# Call libusb_fill_control_transfer() to associate the data buffer with
364 * the transfer (and to set the remaining details such as callback and timeout).
365 * - Note that there is no parameter to set the length field of the transfer.
366 * The length is automatically inferred from the wLength field of the setup
368 * -# Submit the transfer.
370 * The multi-byte control setup fields (wValue, wIndex and wLength) must
371 * be given in little-endian byte order (the endianness of the USB bus).
372 * Endianness conversion is transparently handled by
373 * libusb_fill_control_setup() which is documented to accept host-endian
376 * Further considerations are needed when handling transfer completion in
377 * your callback function:
378 * - As you might expect, the setup packet will still be sitting at the start
379 * of the data buffer.
380 * - If this was a device-to-host transfer, the received data will be sitting
381 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
382 * - The actual_length field of the transfer structure is relative to the
383 * wLength of the setup packet, rather than the size of the data buffer. So,
384 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
385 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
386 * transferred in entirity.
388 * To simplify parsing of setup packets and obtaining the data from the
389 * correct offset, you may wish to use the libusb_control_transfer_get_data()
390 * and libusb_control_transfer_get_setup() functions within your transfer
393 * Even though control endpoints do not halt, a completed control transfer
394 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
395 * request was not supported.
397 * \section asyncintr Considerations for interrupt transfers
399 * All interrupt transfers are performed using the polling interval presented
400 * by the bInterval value of the endpoint descriptor.
402 * \section asynciso Considerations for isochronous transfers
404 * Isochronous transfers are more complicated than transfers to
405 * non-isochronous endpoints.
407 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
408 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
410 * During filling, set \ref libusb_transfer::type "type" to
411 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
412 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
413 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
414 * or equal to the number of packets you requested during allocation.
415 * libusb_alloc_transfer() does not set either of these fields for you, given
416 * that you might not even use the transfer on an isochronous endpoint.
418 * Next, populate the length field for the first num_iso_packets entries in
419 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
420 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
421 * packet length is determined by the wMaxPacketSize field in the endpoint
423 * Two functions can help you here:
425 * - libusb_get_max_iso_packet_size() is an easy way to determine the max
426 * packet size for an isochronous endpoint. Note that the maximum packet
427 * size is actually the maximum number of bytes that can be transmitted in
428 * a single microframe, therefore this function multiplies the maximum number
429 * of bytes per transaction by the number of transaction opportunities per
431 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
432 * within a transfer, which is usually what you want.
434 * For outgoing transfers, you'll obviously fill the buffer and populate the
435 * packet descriptors in hope that all the data gets transferred. For incoming
436 * transfers, you must ensure the buffer has sufficient capacity for
437 * the situation where all packets transfer the full amount of requested data.
439 * Completion handling requires some extra consideration. The
440 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
441 * is meaningless and should not be examined; instead you must refer to the
442 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
443 * each individual packet.
445 * The \ref libusb_transfer::status "status" field of the transfer is also a
447 * - If the packets were submitted and the isochronous data microframes
448 * completed normally, status will have value
449 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
450 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
451 * delays are not counted as transfer errors; the transfer.status field may
452 * indicate COMPLETED even if some or all of the packets failed. Refer to
453 * the \ref libusb_iso_packet_descriptor::status "status" field of each
454 * individual packet to determine packet failures.
455 * - The status field will have value
456 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
457 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
458 * - Other transfer status codes occur with normal behaviour.
460 * The data for each packet will be found at an offset into the buffer that
461 * can be calculated as if each prior packet completed in full. The
462 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
463 * functions may help you here.
465 * <b>Note</b>: Some operating systems (e.g. Linux) may impose limits on the
466 * length of individual isochronous packets and/or the total length of the
467 * isochronous transfer. Such limits can be difficult for libusb to detect,
468 * so the library will simply try and submit the transfer as set up by you.
469 * If the transfer fails to submit because it is too large,
470 * libusb_submit_transfer() will return
471 * \ref libusb_error::LIBUSB_ERROR_INVALID_PARAM "LIBUSB_ERROR_INVALID_PARAM".
473 * \section asyncmem Memory caveats
475 * In most circumstances, it is not safe to use stack memory for transfer
476 * buffers. This is because the function that fired off the asynchronous
477 * transfer may return before libusb has finished using the buffer, and when
478 * the function returns it's stack gets destroyed. This is true for both
479 * host-to-device and device-to-host transfers.
481 * The only case in which it is safe to use stack memory is where you can
482 * guarantee that the function owning the stack space for the buffer does not
483 * return until after the transfer's callback function has completed. In every
484 * other case, you need to use heap memory instead.
486 * \section asyncflags Fine control
488 * Through using this asynchronous interface, you may find yourself repeating
489 * a few simple operations many times. You can apply a bitwise OR of certain
490 * flags to a transfer to simplify certain things:
491 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
492 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
493 * less than the requested amount of data being marked with status
494 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
495 * (they would normally be regarded as COMPLETED)
496 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
497 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
498 * buffer when freeing the transfer.
499 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
500 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
501 * transfer after the transfer callback returns.
503 * \section asyncevent Event handling
505 * An asynchronous model requires that libusb perform work at various
506 * points in time - namely processing the results of previously-submitted
507 * transfers and invoking the user-supplied callback function.
509 * This gives rise to the libusb_handle_events() function which your
510 * application must call into when libusb has work do to. This gives libusb
511 * the opportunity to reap pending transfers, invoke callbacks, etc.
513 * There are 2 different approaches to dealing with libusb_handle_events:
515 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
517 * -# Integrate libusb with your application's main event loop. libusb
518 * exposes a set of file descriptors which allow you to do this.
520 * The first approach has the big advantage that it will also work on Windows
521 * were libusb' poll API for select / poll integration is not available. So
522 * if you want to support Windows and use the async API, you must use this
523 * approach, see the \ref eventthread "Using an event handling thread" section
526 * If you prefer a single threaded approach with a single central event loop,
527 * see the \ref libusb_poll "polling and timing" section for how to integrate libusb
528 * into your application's main event loop.
530 * \section eventthread Using an event handling thread
532 * Lets begin with stating the obvious: If you're going to use a separate
533 * thread for libusb event handling, your callback functions MUST be
536 * Other then that doing event handling from a separate thread, is mostly
537 * simple. You can use an event thread function as follows:
539 void *event_thread_func(void *ctx)
541 while (event_thread_run)
542 libusb_handle_events(ctx);
548 * There is one caveat though, stopping this thread requires setting the
549 * event_thread_run variable to 0, and after that libusb_handle_events() needs
550 * to return control to event_thread_func. But unless some event happens,
551 * libusb_handle_events() will not return.
553 * There are 2 different ways of dealing with this, depending on if your
554 * application uses libusb' \ref libusb_hotplug "hotplug" support or not.
556 * Applications which do not use hotplug support, should not start the event
557 * thread until after their first call to libusb_open(), and should stop the
558 * thread when closing the last open device as follows:
560 void my_close_handle(libusb_device_handle *dev_handle)
563 event_thread_run = 0;
565 libusb_close(dev_handle); // This wakes up libusb_handle_events()
568 pthread_join(event_thread);
574 * Applications using hotplug support should start the thread at program init,
575 * after having successfully called libusb_hotplug_register_callback(), and
576 * should stop the thread at program exit as follows:
578 void my_libusb_exit(void)
580 event_thread_run = 0;
581 libusb_hotplug_deregister_callback(ctx, hotplug_cb_handle); // This wakes up libusb_handle_events()
582 pthread_join(event_thread);
589 * @defgroup libusb_poll Polling and timing
591 * This page documents libusb's functions for polling events and timing.
592 * These functions are only necessary for users of the
593 * \ref libusb_asyncio "asynchronous API". If you are only using the simpler
594 * \ref libusb_syncio "synchronous API" then you do not need to ever call these
597 * The justification for the functionality described here has already been
598 * discussed in the \ref asyncevent "event handling" section of the
599 * asynchronous API documentation. In summary, libusb does not create internal
600 * threads for event processing and hence relies on your application calling
601 * into libusb at certain points in time so that pending events can be handled.
603 * Your main loop is probably already calling poll() or select() or a
604 * variant on a set of file descriptors for other event sources (e.g. keyboard
605 * button presses, mouse movements, network sockets, etc). You then add
606 * libusb's file descriptors to your poll()/select() calls, and when activity
607 * is detected on such descriptors you know it is time to call
608 * libusb_handle_events().
610 * There is one final event handling complication. libusb supports
611 * asynchronous transfers which time out after a specified time period.
613 * On some platforms a timerfd is used, so the timeout handling is just another
614 * fd, on other platforms this requires that libusb is called into at or after
615 * the timeout to handle it. So, in addition to considering libusb's file
616 * descriptors in your main event loop, you must also consider that libusb
617 * sometimes needs to be called into at fixed points in time even when there
618 * is no file descriptor activity, see \ref polltime details.
620 * In order to know precisely when libusb needs to be called into, libusb
621 * offers you a set of pollable file descriptors and information about when
622 * the next timeout expires.
624 * If you are using the asynchronous I/O API, you must take one of the two
625 * following options, otherwise your I/O will not complete.
627 * \section pollsimple The simple option
629 * If your application revolves solely around libusb and does not need to
630 * handle other event sources, you can have a program structure as follows:
633 // find and open device
634 // maybe fire off some initial async I/O
636 while (user_has_not_requested_exit)
637 libusb_handle_events(ctx);
642 * With such a simple main loop, you do not have to worry about managing
643 * sets of file descriptors or handling timeouts. libusb_handle_events() will
644 * handle those details internally.
646 * \section libusb_pollmain The more advanced option
648 * \note This functionality is currently only available on Unix-like platforms.
649 * On Windows, libusb_get_pollfds() simply returns NULL. Applications which
650 * want to support Windows are advised to use an \ref eventthread
651 * "event handling thread" instead.
653 * In more advanced applications, you will already have a main loop which
654 * is monitoring other event sources: network sockets, X11 events, mouse
655 * movements, etc. Through exposing a set of file descriptors, libusb is
656 * designed to cleanly integrate into such main loops.
658 * In addition to polling file descriptors for the other event sources, you
659 * take a set of file descriptors from libusb and monitor those too. When you
660 * detect activity on libusb's file descriptors, you call
661 * libusb_handle_events_timeout() in non-blocking mode.
663 * What's more, libusb may also need to handle events at specific moments in
664 * time. No file descriptor activity is generated at these times, so your
665 * own application needs to be continually aware of when the next one of these
666 * moments occurs (through calling libusb_get_next_timeout()), and then it
667 * needs to call libusb_handle_events_timeout() in non-blocking mode when
668 * these moments occur. This means that you need to adjust your
669 * poll()/select() timeout accordingly.
671 * libusb provides you with a set of file descriptors to poll and expects you
672 * to poll all of them, treating them as a single entity. The meaning of each
673 * file descriptor in the set is an internal implementation detail,
674 * platform-dependent and may vary from release to release. Don't try and
675 * interpret the meaning of the file descriptors, just do as libusb indicates,
676 * polling all of them at once.
678 * In pseudo-code, you want something that looks like:
682 libusb_get_pollfds(ctx)
683 while (user has not requested application exit) {
684 libusb_get_next_timeout(ctx);
685 poll(on libusb file descriptors plus any other event sources of interest,
686 using a timeout no larger than the value libusb just suggested)
687 if (poll() indicated activity on libusb file descriptors)
688 libusb_handle_events_timeout(ctx, &zero_tv);
689 if (time has elapsed to or beyond the libusb timeout)
690 libusb_handle_events_timeout(ctx, &zero_tv);
691 // handle events from other sources here
697 * \subsection polltime Notes on time-based events
699 * The above complication with having to track time and call into libusb at
700 * specific moments is a bit of a headache. For maximum compatibility, you do
701 * need to write your main loop as above, but you may decide that you can
702 * restrict the supported platforms of your application and get away with
703 * a more simplistic scheme.
705 * These time-based event complications are \b not required on the following
708 * - Linux, provided that the following version requirements are satisfied:
709 * - Linux v2.6.27 or newer, compiled with timerfd support
710 * - glibc v2.9 or newer
711 * - libusb v1.0.5 or newer
713 * Under these configurations, libusb_get_next_timeout() will \em always return
714 * 0, so your main loop can be simplified to:
718 libusb_get_pollfds(ctx)
719 while (user has not requested application exit) {
720 poll(on libusb file descriptors plus any other event sources of interest,
721 using any timeout that you like)
722 if (poll() indicated activity on libusb file descriptors)
723 libusb_handle_events_timeout(ctx, &zero_tv);
724 // handle events from other sources here
730 * Do remember that if you simplify your main loop to the above, you will
731 * lose compatibility with some platforms (including legacy Linux platforms,
732 * and <em>any future platforms supported by libusb which may have time-based
733 * event requirements</em>). The resultant problems will likely appear as
734 * strange bugs in your application.
736 * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
737 * check to see if it is safe to ignore the time-based event complications.
738 * If your application has taken the shortcut of ignoring libusb's next timeout
739 * in your main loop, then you are advised to check the return value of
740 * libusb_pollfds_handle_timeouts() during application startup, and to abort
741 * if the platform does suffer from these timing complications.
743 * \subsection fdsetchange Changes in the file descriptor set
745 * The set of file descriptors that libusb uses as event sources may change
746 * during the life of your application. Rather than having to repeatedly
747 * call libusb_get_pollfds(), you can set up notification functions for when
748 * the file descriptor set changes using libusb_set_pollfd_notifiers().
750 * \subsection mtissues Multi-threaded considerations
752 * Unfortunately, the situation is complicated further when multiple threads
753 * come into play. If two threads are monitoring the same file descriptors,
754 * the fact that only one thread will be woken up when an event occurs causes
757 * The events lock, event waiters lock, and libusb_handle_events_locked()
758 * entities are added to solve these problems. You do not need to be concerned
759 * with these entities otherwise.
761 * See the extra documentation: \ref libusb_mtasync
764 /** \page libusb_mtasync Multi-threaded applications and asynchronous I/O
766 * libusb is a thread-safe library, but extra considerations must be applied
767 * to applications which interact with libusb from multiple threads.
769 * The underlying issue that must be addressed is that all libusb I/O
770 * revolves around monitoring file descriptors through the poll()/select()
771 * system calls. This is directly exposed at the
772 * \ref libusb_asyncio "asynchronous interface" but it is important to note that the
773 * \ref libusb_syncio "synchronous interface" is implemented on top of the
774 * asynchonrous interface, therefore the same considerations apply.
776 * The issue is that if two or more threads are concurrently calling poll()
777 * or select() on libusb's file descriptors then only one of those threads
778 * will be woken up when an event arrives. The others will be completely
779 * oblivious that anything has happened.
781 * Consider the following pseudo-code, which submits an asynchronous transfer
782 * then waits for its completion. This style is one way you could implement a
783 * synchronous interface on top of the asynchronous interface (and libusb
784 * does something similar, albeit more advanced due to the complications
785 * explained on this page).
788 void cb(struct libusb_transfer *transfer)
790 int *completed = transfer->user_data;
795 struct libusb_transfer *transfer;
796 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE] __attribute__ ((aligned (2)));
799 transfer = libusb_alloc_transfer(0);
800 libusb_fill_control_setup(buffer,
801 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
802 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
803 libusb_submit_transfer(transfer);
806 poll(libusb file descriptors, 120*1000);
807 if (poll indicates activity)
808 libusb_handle_events_timeout(ctx, &zero_tv);
810 printf("completed!");
815 * Here we are <em>serializing</em> completion of an asynchronous event
816 * against a condition - the condition being completion of a specific transfer.
817 * The poll() loop has a long timeout to minimize CPU usage during situations
818 * when nothing is happening (it could reasonably be unlimited).
820 * If this is the only thread that is polling libusb's file descriptors, there
821 * is no problem: there is no danger that another thread will swallow up the
822 * event that we are interested in. On the other hand, if there is another
823 * thread polling the same descriptors, there is a chance that it will receive
824 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
825 * will only realise that the transfer has completed on the next iteration of
826 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
827 * undesirable, and don't even think about using short timeouts to circumvent
830 * The solution here is to ensure that no two threads are ever polling the
831 * file descriptors at the same time. A naive implementation of this would
832 * impact the capabilities of the library, so libusb offers the scheme
833 * documented below to ensure no loss of functionality.
835 * Before we go any further, it is worth mentioning that all libusb-wrapped
836 * event handling procedures fully adhere to the scheme documented below.
837 * This includes libusb_handle_events() and its variants, and all the
838 * synchronous I/O functions - libusb hides this headache from you.
840 * \section Using libusb_handle_events() from multiple threads
842 * Even when only using libusb_handle_events() and synchronous I/O functions,
843 * you can still have a race condition. You might be tempted to solve the
844 * above with libusb_handle_events() like so:
847 libusb_submit_transfer(transfer);
850 libusb_handle_events(ctx);
852 printf("completed!");
855 * This however has a race between the checking of completed and
856 * libusb_handle_events() acquiring the events lock, so another thread
857 * could have completed the transfer, resulting in this thread hanging
858 * until either a timeout or another event occurs. See also commit
859 * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
860 * synchronous API implementation of libusb.
862 * Fixing this race requires checking the variable completed only after
863 * taking the event lock, which defeats the concept of just calling
864 * libusb_handle_events() without worrying about locking. This is why
865 * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
866 * and libusb_handle_events_completed() functions, which handles doing the
867 * completion check for you after they have acquired the lock:
870 libusb_submit_transfer(transfer);
873 libusb_handle_events_completed(ctx, &completed);
875 printf("completed!");
878 * This nicely fixes the race in our example. Note that if all you want to
879 * do is submit a single transfer and wait for its completion, then using
880 * one of the synchronous I/O functions is much easier.
882 * \section eventlock The events lock
884 * The problem is when we consider the fact that libusb exposes file
885 * descriptors to allow for you to integrate asynchronous USB I/O into
886 * existing main loops, effectively allowing you to do some work behind
887 * libusb's back. If you do take libusb's file descriptors and pass them to
888 * poll()/select() yourself, you need to be aware of the associated issues.
890 * The first concept to be introduced is the events lock. The events lock
891 * is used to serialize threads that want to handle events, such that only
892 * one thread is handling events at any one time.
894 * You must take the events lock before polling libusb file descriptors,
895 * using libusb_lock_events(). You must release the lock as soon as you have
896 * aborted your poll()/select() loop, using libusb_unlock_events().
898 * \section threadwait Letting other threads do the work for you
900 * Although the events lock is a critical part of the solution, it is not
901 * enough on it's own. You might wonder if the following is sufficient...
903 libusb_lock_events(ctx);
905 poll(libusb file descriptors, 120*1000);
906 if (poll indicates activity)
907 libusb_handle_events_timeout(ctx, &zero_tv);
909 libusb_unlock_events(ctx);
911 * ...and the answer is that it is not. This is because the transfer in the
912 * code shown above may take a long time (say 30 seconds) to complete, and
913 * the lock is not released until the transfer is completed.
915 * Another thread with similar code that wants to do event handling may be
916 * working with a transfer that completes after a few milliseconds. Despite
917 * having such a quick completion time, the other thread cannot check that
918 * status of its transfer until the code above has finished (30 seconds later)
919 * due to contention on the lock.
921 * To solve this, libusb offers you a mechanism to determine when another
922 * thread is handling events. It also offers a mechanism to block your thread
923 * until the event handling thread has completed an event (and this mechanism
924 * does not involve polling of file descriptors).
926 * After determining that another thread is currently handling events, you
927 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
928 * You then re-check that some other thread is still handling events, and if
929 * so, you call libusb_wait_for_event().
931 * libusb_wait_for_event() puts your application to sleep until an event
932 * occurs, or until a thread releases the events lock. When either of these
933 * things happen, your thread is woken up, and should re-check the condition
934 * it was waiting on. It should also re-check that another thread is handling
935 * events, and if not, it should start handling events itself.
937 * This looks like the following, as pseudo-code:
940 if (libusb_try_lock_events(ctx) == 0) {
941 // we obtained the event lock: do our own event handling
943 if (!libusb_event_handling_ok(ctx)) {
944 libusb_unlock_events(ctx);
947 poll(libusb file descriptors, 120*1000);
948 if (poll indicates activity)
949 libusb_handle_events_locked(ctx, 0);
951 libusb_unlock_events(ctx);
953 // another thread is doing event handling. wait for it to signal us that
954 // an event has completed
955 libusb_lock_event_waiters(ctx);
958 // now that we have the event waiters lock, double check that another
959 // thread is still handling events for us. (it may have ceased handling
960 // events in the time it took us to reach this point)
961 if (!libusb_event_handler_active(ctx)) {
962 // whoever was handling events is no longer doing so, try again
963 libusb_unlock_event_waiters(ctx);
967 libusb_wait_for_event(ctx, NULL);
969 libusb_unlock_event_waiters(ctx);
971 printf("completed!\n");
974 * A naive look at the above code may suggest that this can only support
975 * one event waiter (hence a total of 2 competing threads, the other doing
976 * event handling), because the event waiter seems to have taken the event
977 * waiters lock while waiting for an event. However, the system does support
978 * multiple event waiters, because libusb_wait_for_event() actually drops
979 * the lock while waiting, and reaquires it before continuing.
981 * We have now implemented code which can dynamically handle situations where
982 * nobody is handling events (so we should do it ourselves), and it can also
983 * handle situations where another thread is doing event handling (so we can
984 * piggyback onto them). It is also equipped to handle a combination of
985 * the two, for example, another thread is doing event handling, but for
986 * whatever reason it stops doing so before our condition is met, so we take
987 * over the event handling.
989 * Four functions were introduced in the above pseudo-code. Their importance
990 * should be apparent from the code shown above.
991 * -# libusb_try_lock_events() is a non-blocking function which attempts
992 * to acquire the events lock but returns a failure code if it is contended.
993 * -# libusb_event_handling_ok() checks that libusb is still happy for your
994 * thread to be performing event handling. Sometimes, libusb needs to
995 * interrupt the event handler, and this is how you can check if you have
996 * been interrupted. If this function returns 0, the correct behaviour is
997 * for you to give up the event handling lock, and then to repeat the cycle.
998 * The following libusb_try_lock_events() will fail, so you will become an
999 * events waiter. For more information on this, read \ref fullstory below.
1000 * -# libusb_handle_events_locked() is a variant of
1001 * libusb_handle_events_timeout() that you can call while holding the
1002 * events lock. libusb_handle_events_timeout() itself implements similar
1003 * logic to the above, so be sure not to call it when you are
1004 * "working behind libusb's back", as is the case here.
1005 * -# libusb_event_handler_active() determines if someone is currently
1006 * holding the events lock
1008 * You might be wondering why there is no function to wake up all threads
1009 * blocked on libusb_wait_for_event(). This is because libusb can do this
1010 * internally: it will wake up all such threads when someone calls
1011 * libusb_unlock_events() or when a transfer completes (at the point after its
1012 * callback has returned).
1014 * \subsection fullstory The full story
1016 * The above explanation should be enough to get you going, but if you're
1017 * really thinking through the issues then you may be left with some more
1018 * questions regarding libusb's internals. If you're curious, read on, and if
1019 * not, skip to the next section to avoid confusing yourself!
1021 * The immediate question that may spring to mind is: what if one thread
1022 * modifies the set of file descriptors that need to be polled while another
1023 * thread is doing event handling?
1025 * There are 2 situations in which this may happen.
1026 * -# libusb_open() will add another file descriptor to the poll set,
1027 * therefore it is desirable to interrupt the event handler so that it
1028 * restarts, picking up the new descriptor.
1029 * -# libusb_close() will remove a file descriptor from the poll set. There
1030 * are all kinds of race conditions that could arise here, so it is
1031 * important that nobody is doing event handling at this time.
1033 * libusb handles these issues internally, so application developers do not
1034 * have to stop their event handlers while opening/closing devices. Here's how
1035 * it works, focusing on the libusb_close() situation first:
1037 * -# During initialization, libusb opens an internal pipe, and it adds the read
1038 * end of this pipe to the set of file descriptors to be polled.
1039 * -# During libusb_close(), libusb writes some dummy data on this event pipe.
1040 * This immediately interrupts the event handler. libusb also records
1041 * internally that it is trying to interrupt event handlers for this
1042 * high-priority event.
1043 * -# At this point, some of the functions described above start behaving
1045 * - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
1046 * OK for event handling to continue.
1047 * - libusb_try_lock_events() starts returning 1, indicating that another
1048 * thread holds the event handling lock, even if the lock is uncontended.
1049 * - libusb_event_handler_active() starts returning 1, indicating that
1050 * another thread is doing event handling, even if that is not true.
1051 * -# The above changes in behaviour result in the event handler stopping and
1052 * giving up the events lock very quickly, giving the high-priority
1053 * libusb_close() operation a "free ride" to acquire the events lock. All
1054 * threads that are competing to do event handling become event waiters.
1055 * -# With the events lock held inside libusb_close(), libusb can safely remove
1056 * a file descriptor from the poll set, in the safety of knowledge that
1057 * nobody is polling those descriptors or trying to access the poll set.
1058 * -# After obtaining the events lock, the close operation completes very
1059 * quickly (usually a matter of milliseconds) and then immediately releases
1061 * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
1062 * reverts to the original, documented behaviour.
1063 * -# The release of the events lock causes the threads that are waiting for
1064 * events to be woken up and to start competing to become event handlers
1065 * again. One of them will succeed; it will then re-obtain the list of poll
1066 * descriptors, and USB I/O will then continue as normal.
1068 * libusb_open() is similar, and is actually a more simplistic case. Upon a
1069 * call to libusb_open():
1071 * -# The device is opened and a file descriptor is added to the poll set.
1072 * -# libusb sends some dummy data on the event pipe, and records that it
1073 * is trying to modify the poll descriptor set.
1074 * -# The event handler is interrupted, and the same behaviour change as for
1075 * libusb_close() takes effect, causing all event handling threads to become
1077 * -# The libusb_open() implementation takes its free ride to the events lock.
1078 * -# Happy that it has successfully paused the events handler, libusb_open()
1079 * releases the events lock.
1080 * -# The event waiter threads are all woken up and compete to become event
1081 * handlers again. The one that succeeds will obtain the list of poll
1082 * descriptors again, which will include the addition of the new device.
1084 * \subsection concl Closing remarks
1086 * The above may seem a little complicated, but hopefully I have made it clear
1087 * why such complications are necessary. Also, do not forget that this only
1088 * applies to applications that take libusb's file descriptors and integrate
1089 * them into their own polling loops.
1091 * You may decide that it is OK for your multi-threaded application to ignore
1092 * some of the rules and locks detailed above, because you don't think that
1093 * two threads can ever be polling the descriptors at the same time. If that
1094 * is the case, then that's good news for you because you don't have to worry.
1095 * But be careful here; remember that the synchronous I/O functions do event
1096 * handling internally. If you have one thread doing event handling in a loop
1097 * (without implementing the rules and locking semantics documented above)
1098 * and another trying to send a synchronous USB transfer, you will end up with
1099 * two threads monitoring the same descriptors, and the above-described
1100 * undesirable behaviour occurring. The solution is for your polling thread to
1101 * play by the rules; the synchronous I/O functions do so, and this will result
1102 * in them getting along in perfect harmony.
1104 * If you do have a dedicated thread doing event handling, it is perfectly
1105 * legal for it to take the event handling lock for long periods of time. Any
1106 * synchronous I/O functions you call from other threads will transparently
1107 * fall back to the "event waiters" mechanism detailed above. The only
1108 * consideration that your event handling thread must apply is the one related
1109 * to libusb_event_handling_ok(): you must call this before every poll(), and
1110 * give up the events lock if instructed.
1113 int usbi_io_init(struct libusb_context *ctx)
1117 usbi_mutex_init(&ctx->flying_transfers_lock);
1118 usbi_mutex_init(&ctx->events_lock);
1119 usbi_mutex_init(&ctx->event_waiters_lock);
1120 usbi_cond_init(&ctx->event_waiters_cond);
1121 usbi_mutex_init(&ctx->event_data_lock);
1122 usbi_tls_key_create(&ctx->event_handling_key);
1123 list_init(&ctx->flying_transfers);
1124 list_init(&ctx->ipollfds);
1125 list_init(&ctx->removed_ipollfds);
1126 list_init(&ctx->hotplug_msgs);
1127 list_init(&ctx->completed_transfers);
1129 /* FIXME should use an eventfd on kernels that support it */
1130 r = usbi_pipe(ctx->event_pipe);
1132 r = LIBUSB_ERROR_OTHER;
1136 r = usbi_add_pollfd(ctx, ctx->event_pipe[0], POLLIN);
1138 goto err_close_pipe;
1141 ctx->timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
1142 if (ctx->timerfd >= 0) {
1143 usbi_dbg("using timerfd for timeouts");
1144 r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
1146 goto err_close_timerfd;
1148 usbi_dbg("timerfd not available, errno=%d", errno);
1156 close(ctx->timerfd);
1157 usbi_remove_pollfd(ctx, ctx->event_pipe[0]);
1160 usbi_close(ctx->event_pipe[0]);
1161 usbi_close(ctx->event_pipe[1]);
1163 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1164 usbi_mutex_destroy(&ctx->events_lock);
1165 usbi_mutex_destroy(&ctx->event_waiters_lock);
1166 usbi_cond_destroy(&ctx->event_waiters_cond);
1167 usbi_mutex_destroy(&ctx->event_data_lock);
1168 usbi_tls_key_delete(ctx->event_handling_key);
1172 static void cleanup_removed_pollfds(struct libusb_context *ctx)
1174 struct usbi_pollfd *ipollfd, *tmp;
1175 list_for_each_entry_safe(ipollfd, tmp, &ctx->removed_ipollfds, list, struct usbi_pollfd) {
1176 list_del(&ipollfd->list);
1181 void usbi_io_exit(struct libusb_context *ctx)
1183 usbi_remove_pollfd(ctx, ctx->event_pipe[0]);
1184 usbi_close(ctx->event_pipe[0]);
1185 usbi_close(ctx->event_pipe[1]);
1187 if (usbi_using_timerfd(ctx)) {
1188 usbi_remove_pollfd(ctx, ctx->timerfd);
1189 close(ctx->timerfd);
1192 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1193 usbi_mutex_destroy(&ctx->events_lock);
1194 usbi_mutex_destroy(&ctx->event_waiters_lock);
1195 usbi_cond_destroy(&ctx->event_waiters_cond);
1196 usbi_mutex_destroy(&ctx->event_data_lock);
1197 usbi_tls_key_delete(ctx->event_handling_key);
1199 cleanup_removed_pollfds(ctx);
1202 static int calculate_timeout(struct usbi_transfer *itransfer)
1205 struct timespec current_time;
1206 unsigned int timeout =
1207 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout;
1210 timerclear(&itransfer->timeout);
1214 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, ¤t_time);
1216 usbi_err(ITRANSFER_CTX(itransfer),
1217 "failed to read monotonic clock, errno=%d", errno);
1221 current_time.tv_sec += timeout / 1000;
1222 current_time.tv_nsec += (timeout % 1000) * 1000000;
1224 while (current_time.tv_nsec >= 1000000000) {
1225 current_time.tv_nsec -= 1000000000;
1226 current_time.tv_sec++;
1229 TIMESPEC_TO_TIMEVAL(&itransfer->timeout, ¤t_time);
1233 /** \ingroup libusb_asyncio
1234 * Allocate a libusb transfer with a specified number of isochronous packet
1235 * descriptors. The returned transfer is pre-initialized for you. When the new
1236 * transfer is no longer needed, it should be freed with
1237 * libusb_free_transfer().
1239 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
1240 * interrupt) should specify an iso_packets count of zero.
1242 * For transfers intended for isochronous endpoints, specify an appropriate
1243 * number of packet descriptors to be allocated as part of the transfer.
1244 * The returned transfer is not specially initialized for isochronous I/O;
1245 * you are still required to set the
1246 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
1247 * \ref libusb_transfer::type "type" fields accordingly.
1249 * It is safe to allocate a transfer with some isochronous packets and then
1250 * use it on a non-isochronous endpoint. If you do this, ensure that at time
1251 * of submission, num_iso_packets is 0 and that type is set appropriately.
1253 * \param iso_packets number of isochronous packet descriptors to allocate. Must be non-negative.
1254 * \returns a newly allocated transfer, or NULL on error
1257 struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
1260 struct libusb_transfer *transfer;
1261 size_t os_alloc_size;
1263 struct usbi_transfer *itransfer;
1265 assert(iso_packets >= 0);
1267 os_alloc_size = usbi_backend.transfer_priv_size;
1268 alloc_size = sizeof(struct usbi_transfer)
1269 + sizeof(struct libusb_transfer)
1270 + (sizeof(struct libusb_iso_packet_descriptor) * (size_t)iso_packets)
1272 itransfer = calloc(1, alloc_size);
1276 itransfer->num_iso_packets = iso_packets;
1277 usbi_mutex_init(&itransfer->lock);
1278 transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1279 usbi_dbg("transfer %p", transfer);
1283 /** \ingroup libusb_asyncio
1284 * Free a transfer structure. This should be called for all transfers
1285 * allocated with libusb_alloc_transfer().
1287 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
1288 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
1289 * non-NULL, this function will also free the transfer buffer using the
1290 * standard system memory allocator (e.g. free()).
1292 * It is legal to call this function with a NULL transfer. In this case,
1293 * the function will simply return safely.
1295 * It is not legal to free an active transfer (one which has been submitted
1296 * and has not yet completed).
1298 * \param transfer the transfer to free
1300 void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
1302 struct usbi_transfer *itransfer;
1306 usbi_dbg("transfer %p", transfer);
1307 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER)
1308 free(transfer->buffer);
1310 itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1311 usbi_mutex_destroy(&itransfer->lock);
1316 static int disarm_timerfd(struct libusb_context *ctx)
1318 const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
1322 r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
1324 return LIBUSB_ERROR_OTHER;
1329 /* iterates through the flying transfers, and rearms the timerfd based on the
1330 * next upcoming timeout.
1331 * must be called with flying_list locked.
1332 * returns 0 on success or a LIBUSB_ERROR code on failure.
1334 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1336 struct usbi_transfer *itransfer;
1338 list_for_each_entry(itransfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1339 struct timeval *cur_tv = &itransfer->timeout;
1341 /* if we've reached transfers of infinite timeout, then we have no
1343 if (!timerisset(cur_tv))
1346 /* act on first transfer that has not already been handled */
1347 if (!(itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))) {
1349 const struct itimerspec it = { {0, 0},
1350 { cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
1351 usbi_dbg("next timeout originally %dms", USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout);
1352 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1354 return LIBUSB_ERROR_OTHER;
1360 return disarm_timerfd(ctx);
1363 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1370 /* add a transfer to the (timeout-sorted) active transfers list.
1371 * This function will return non 0 if fails to update the timer,
1372 * in which case the transfer is *not* on the flying_transfers list. */
1373 static int add_to_flying_list(struct usbi_transfer *itransfer)
1375 struct usbi_transfer *cur;
1376 struct timeval *timeout = &itransfer->timeout;
1377 struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
1381 r = calculate_timeout(itransfer);
1385 /* if we have no other flying transfers, start the list with this one */
1386 if (list_empty(&ctx->flying_transfers)) {
1387 list_add(&itransfer->list, &ctx->flying_transfers);
1391 /* if we have infinite timeout, append to end of list */
1392 if (!timerisset(timeout)) {
1393 list_add_tail(&itransfer->list, &ctx->flying_transfers);
1394 /* first is irrelevant in this case */
1398 /* otherwise, find appropriate place in list */
1399 list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
1400 /* find first timeout that occurs after the transfer in question */
1401 struct timeval *cur_tv = &cur->timeout;
1403 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
1404 (cur_tv->tv_sec == timeout->tv_sec &&
1405 cur_tv->tv_usec > timeout->tv_usec)) {
1406 list_add_tail(&itransfer->list, &cur->list);
1411 /* first is 0 at this stage (list not empty) */
1413 /* otherwise we need to be inserted at the end */
1414 list_add_tail(&itransfer->list, &ctx->flying_transfers);
1417 if (first && usbi_using_timerfd(ctx) && timerisset(timeout)) {
1418 /* if this transfer has the lowest timeout of all active transfers,
1419 * rearm the timerfd with this transfer's timeout */
1420 const struct itimerspec it = { {0, 0},
1421 { timeout->tv_sec, timeout->tv_usec * 1000 } };
1422 usbi_dbg("arm timerfd for timeout in %dms (first in line)",
1423 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout);
1424 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1426 usbi_warn(ctx, "failed to arm first timerfd, errno=%d", errno);
1427 r = LIBUSB_ERROR_OTHER;
1435 list_del(&itransfer->list);
1440 /* remove a transfer from the active transfers list.
1441 * This function will *always* remove the transfer from the
1442 * flying_transfers list. It will return a LIBUSB_ERROR code
1443 * if it fails to update the timer for the next timeout. */
1444 static int remove_from_flying_list(struct usbi_transfer *itransfer)
1446 struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
1450 usbi_mutex_lock(&ctx->flying_transfers_lock);
1451 rearm_timerfd = (timerisset(&itransfer->timeout) &&
1452 list_first_entry(&ctx->flying_transfers, struct usbi_transfer, list) == itransfer);
1453 list_del(&itransfer->list);
1454 if (usbi_using_timerfd(ctx) && rearm_timerfd)
1455 r = arm_timerfd_for_next_timeout(ctx);
1456 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1461 /** \ingroup libusb_asyncio
1462 * Submit a transfer. This function will fire off the USB transfer and then
1463 * return immediately.
1465 * \param transfer the transfer to submit
1466 * \returns 0 on success
1467 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
1468 * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
1469 * \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
1470 * by the operating system.
1471 * \returns LIBUSB_ERROR_INVALID_PARAM if the transfer size is larger than
1472 * the operating system and/or hardware can support
1473 * \returns another LIBUSB_ERROR code on other failure
1475 int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
1477 struct usbi_transfer *itransfer =
1478 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1479 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1482 usbi_dbg("transfer %p", transfer);
1485 * Important note on locking, this function takes / releases locks
1486 * in the following order:
1487 * take flying_transfers_lock
1488 * take itransfer->lock
1490 * add to flying_transfers list
1491 * release flying_transfers_lock
1493 * release itransfer->lock
1495 * take flying_transfers_lock
1496 * remove from flying_transfers list
1497 * release flying_transfers_lock
1499 * Note that it takes locks in the order a-b and then releases them
1500 * in the same order a-b. This is somewhat unusual but not wrong,
1501 * release order is not important as long as *all* locks are released
1502 * before re-acquiring any locks.
1504 * This means that the ordering of first releasing itransfer->lock
1505 * and then re-acquiring the flying_transfers_list on error is
1506 * important and must not be changed!
1508 * This is done this way because when we take both locks we must always
1509 * take flying_transfers_lock first to avoid ab-ba style deadlocks with
1510 * the timeout handling and usbi_handle_disconnect paths.
1512 * And we cannot release itransfer->lock before the submission is
1513 * complete otherwise timeout handling for transfers with short
1514 * timeouts may run before submission.
1516 usbi_mutex_lock(&ctx->flying_transfers_lock);
1517 usbi_mutex_lock(&itransfer->lock);
1518 if (itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT) {
1519 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1520 usbi_mutex_unlock(&itransfer->lock);
1521 return LIBUSB_ERROR_BUSY;
1523 itransfer->transferred = 0;
1524 itransfer->state_flags = 0;
1525 itransfer->timeout_flags = 0;
1526 r = add_to_flying_list(itransfer);
1528 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1529 usbi_mutex_unlock(&itransfer->lock);
1533 * We must release the flying transfers lock here, because with
1534 * some backends the submit_transfer method is synchroneous.
1536 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1538 r = usbi_backend.submit_transfer(itransfer);
1539 if (r == LIBUSB_SUCCESS) {
1540 itransfer->state_flags |= USBI_TRANSFER_IN_FLIGHT;
1541 /* keep a reference to this device */
1542 libusb_ref_device(transfer->dev_handle->dev);
1544 usbi_mutex_unlock(&itransfer->lock);
1546 if (r != LIBUSB_SUCCESS)
1547 remove_from_flying_list(itransfer);
1552 /** \ingroup libusb_asyncio
1553 * Asynchronously cancel a previously submitted transfer.
1554 * This function returns immediately, but this does not indicate cancellation
1555 * is complete. Your callback function will be invoked at some later time
1556 * with a transfer status of
1557 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
1558 * "LIBUSB_TRANSFER_CANCELLED."
1560 * \param transfer the transfer to cancel
1561 * \returns 0 on success
1562 * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is not in progress,
1563 * already complete, or already cancelled.
1564 * \returns a LIBUSB_ERROR code on failure
1566 int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
1568 struct usbi_transfer *itransfer =
1569 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1572 usbi_dbg("transfer %p", transfer );
1573 usbi_mutex_lock(&itransfer->lock);
1574 if (!(itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT)
1575 || (itransfer->state_flags & USBI_TRANSFER_CANCELLING)) {
1576 r = LIBUSB_ERROR_NOT_FOUND;
1579 r = usbi_backend.cancel_transfer(itransfer);
1581 if (r != LIBUSB_ERROR_NOT_FOUND &&
1582 r != LIBUSB_ERROR_NO_DEVICE)
1583 usbi_err(TRANSFER_CTX(transfer),
1584 "cancel transfer failed error %d", r);
1586 usbi_dbg("cancel transfer failed error %d", r);
1588 if (r == LIBUSB_ERROR_NO_DEVICE)
1589 itransfer->state_flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
1592 itransfer->state_flags |= USBI_TRANSFER_CANCELLING;
1595 usbi_mutex_unlock(&itransfer->lock);
1599 /** \ingroup libusb_asyncio
1600 * Set a transfers bulk stream id. Note users are advised to use
1601 * libusb_fill_bulk_stream_transfer() instead of calling this function
1604 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1606 * \param transfer the transfer to set the stream id for
1607 * \param stream_id the stream id to set
1608 * \see libusb_alloc_streams()
1610 void API_EXPORTED libusb_transfer_set_stream_id(
1611 struct libusb_transfer *transfer, uint32_t stream_id)
1613 struct usbi_transfer *itransfer =
1614 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1616 itransfer->stream_id = stream_id;
1619 /** \ingroup libusb_asyncio
1620 * Get a transfers bulk stream id.
1622 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1624 * \param transfer the transfer to get the stream id for
1625 * \returns the stream id for the transfer
1627 uint32_t API_EXPORTED libusb_transfer_get_stream_id(
1628 struct libusb_transfer *transfer)
1630 struct usbi_transfer *itransfer =
1631 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1633 return itransfer->stream_id;
1636 /* Handle completion of a transfer (completion might be an error condition).
1637 * This will invoke the user-supplied callback function, which may end up
1638 * freeing the transfer. Therefore you cannot use the transfer structure
1639 * after calling this function, and you should free all backend-specific
1640 * data before calling it.
1641 * Do not call this function with the usbi_transfer lock held. User-specified
1642 * callback functions may attempt to directly resubmit the transfer, which
1643 * will attempt to take the lock. */
1644 int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1645 enum libusb_transfer_status status)
1647 struct libusb_transfer *transfer =
1648 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1649 struct libusb_device_handle *dev_handle = transfer->dev_handle;
1653 r = remove_from_flying_list(itransfer);
1655 usbi_err(ITRANSFER_CTX(itransfer), "failed to set timer for next timeout, errno=%d", errno);
1657 usbi_mutex_lock(&itransfer->lock);
1658 itransfer->state_flags &= ~USBI_TRANSFER_IN_FLIGHT;
1659 usbi_mutex_unlock(&itransfer->lock);
1661 if (status == LIBUSB_TRANSFER_COMPLETED
1662 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1663 int rqlen = transfer->length;
1664 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1665 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1666 if (rqlen != itransfer->transferred) {
1667 usbi_dbg("interpreting short transfer as error");
1668 status = LIBUSB_TRANSFER_ERROR;
1672 flags = transfer->flags;
1673 transfer->status = status;
1674 transfer->actual_length = itransfer->transferred;
1675 usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
1676 if (transfer->callback)
1677 transfer->callback(transfer);
1678 /* transfer might have been freed by the above call, do not use from
1680 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1681 libusb_free_transfer(transfer);
1682 libusb_unref_device(dev_handle->dev);
1686 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1687 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1688 * transfers exist here.
1689 * Do not call this function with the usbi_transfer lock held. User-specified
1690 * callback functions may attempt to directly resubmit the transfer, which
1691 * will attempt to take the lock. */
1692 int usbi_handle_transfer_cancellation(struct usbi_transfer *itransfer)
1694 struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
1697 usbi_mutex_lock(&ctx->flying_transfers_lock);
1698 timed_out = itransfer->timeout_flags & USBI_TRANSFER_TIMED_OUT;
1699 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1701 /* if the URB was cancelled due to timeout, report timeout to the user */
1703 usbi_dbg("detected timeout cancellation");
1704 return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_TIMED_OUT);
1707 /* otherwise its a normal async cancel */
1708 return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_CANCELLED);
1711 /* Add a completed transfer to the completed_transfers list of the
1712 * context and signal the event. The backend's handle_transfer_completion()
1713 * function will be called the next time an event handler runs. */
1714 void usbi_signal_transfer_completion(struct usbi_transfer *itransfer)
1716 libusb_device_handle *dev_handle = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->dev_handle;
1719 struct libusb_context *ctx = HANDLE_CTX(dev_handle);
1722 usbi_mutex_lock(&ctx->event_data_lock);
1723 pending_events = usbi_pending_events(ctx);
1724 list_add_tail(&itransfer->completed_list, &ctx->completed_transfers);
1725 if (!pending_events)
1726 usbi_signal_event(ctx);
1727 usbi_mutex_unlock(&ctx->event_data_lock);
1731 /** \ingroup libusb_poll
1732 * Attempt to acquire the event handling lock. This lock is used to ensure that
1733 * only one thread is monitoring libusb event sources at any one time.
1735 * You only need to use this lock if you are developing an application
1736 * which calls poll() or select() on libusb's file descriptors directly.
1737 * If you stick to libusb's event handling loop functions (e.g.
1738 * libusb_handle_events()) then you do not need to be concerned with this
1741 * While holding this lock, you are trusted to actually be handling events.
1742 * If you are no longer handling events, you must call libusb_unlock_events()
1743 * as soon as possible.
1745 * \param ctx the context to operate on, or NULL for the default context
1746 * \returns 0 if the lock was obtained successfully
1747 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1748 * \ref libusb_mtasync
1750 int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
1755 ctx = usbi_get_context(ctx);
1757 /* is someone else waiting to close a device? if so, don't let this thread
1758 * start event handling */
1759 usbi_mutex_lock(&ctx->event_data_lock);
1760 ru = ctx->device_close;
1761 usbi_mutex_unlock(&ctx->event_data_lock);
1763 usbi_dbg("someone else is closing a device");
1767 r = usbi_mutex_trylock(&ctx->events_lock);
1771 ctx->event_handler_active = 1;
1775 /** \ingroup libusb_poll
1776 * Acquire the event handling lock, blocking until successful acquisition if
1777 * it is contended. This lock is used to ensure that only one thread is
1778 * monitoring libusb event sources at any one time.
1780 * You only need to use this lock if you are developing an application
1781 * which calls poll() or select() on libusb's file descriptors directly.
1782 * If you stick to libusb's event handling loop functions (e.g.
1783 * libusb_handle_events()) then you do not need to be concerned with this
1786 * While holding this lock, you are trusted to actually be handling events.
1787 * If you are no longer handling events, you must call libusb_unlock_events()
1788 * as soon as possible.
1790 * \param ctx the context to operate on, or NULL for the default context
1791 * \ref libusb_mtasync
1793 void API_EXPORTED libusb_lock_events(libusb_context *ctx)
1795 ctx = usbi_get_context(ctx);
1796 usbi_mutex_lock(&ctx->events_lock);
1797 ctx->event_handler_active = 1;
1800 /** \ingroup libusb_poll
1801 * Release the lock previously acquired with libusb_try_lock_events() or
1802 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1803 * on libusb_wait_for_event().
1805 * \param ctx the context to operate on, or NULL for the default context
1806 * \ref libusb_mtasync
1808 void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
1810 ctx = usbi_get_context(ctx);
1811 ctx->event_handler_active = 0;
1812 usbi_mutex_unlock(&ctx->events_lock);
1814 /* FIXME: perhaps we should be a bit more efficient by not broadcasting
1815 * the availability of the events lock when we are modifying pollfds
1816 * (check ctx->device_close)? */
1817 usbi_mutex_lock(&ctx->event_waiters_lock);
1818 usbi_cond_broadcast(&ctx->event_waiters_cond);
1819 usbi_mutex_unlock(&ctx->event_waiters_lock);
1822 /** \ingroup libusb_poll
1823 * Determine if it is still OK for this thread to be doing event handling.
1825 * Sometimes, libusb needs to temporarily pause all event handlers, and this
1826 * is the function you should use before polling file descriptors to see if
1829 * If this function instructs your thread to give up the events lock, you
1830 * should just continue the usual logic that is documented in \ref libusb_mtasync.
1831 * On the next iteration, your thread will fail to obtain the events lock,
1832 * and will hence become an event waiter.
1834 * This function should be called while the events lock is held: you don't
1835 * need to worry about the results of this function if your thread is not
1836 * the current event handler.
1838 * \param ctx the context to operate on, or NULL for the default context
1839 * \returns 1 if event handling can start or continue
1840 * \returns 0 if this thread must give up the events lock
1841 * \ref fullstory "Multi-threaded I/O: the full story"
1843 int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
1847 ctx = usbi_get_context(ctx);
1849 /* is someone else waiting to close a device? if so, don't let this thread
1850 * continue event handling */
1851 usbi_mutex_lock(&ctx->event_data_lock);
1852 r = ctx->device_close;
1853 usbi_mutex_unlock(&ctx->event_data_lock);
1855 usbi_dbg("someone else is closing a device");
1863 /** \ingroup libusb_poll
1864 * Determine if an active thread is handling events (i.e. if anyone is holding
1865 * the event handling lock).
1867 * \param ctx the context to operate on, or NULL for the default context
1868 * \returns 1 if a thread is handling events
1869 * \returns 0 if there are no threads currently handling events
1870 * \ref libusb_mtasync
1872 int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
1876 ctx = usbi_get_context(ctx);
1878 /* is someone else waiting to close a device? if so, don't let this thread
1879 * start event handling -- indicate that event handling is happening */
1880 usbi_mutex_lock(&ctx->event_data_lock);
1881 r = ctx->device_close;
1882 usbi_mutex_unlock(&ctx->event_data_lock);
1884 usbi_dbg("someone else is closing a device");
1888 return ctx->event_handler_active;
1891 /** \ingroup libusb_poll
1892 * Interrupt any active thread that is handling events. This is mainly useful
1893 * for interrupting a dedicated event handling thread when an application
1894 * wishes to call libusb_exit().
1896 * Since version 1.0.21, \ref LIBUSB_API_VERSION >= 0x01000105
1898 * \param ctx the context to operate on, or NULL for the default context
1899 * \ref libusb_mtasync
1901 void API_EXPORTED libusb_interrupt_event_handler(libusb_context *ctx)
1907 ctx = usbi_get_context(ctx);
1908 usbi_mutex_lock(&ctx->event_data_lock);
1910 pending_events = usbi_pending_events(ctx);
1911 ctx->event_flags |= USBI_EVENT_USER_INTERRUPT;
1912 if (!pending_events)
1913 usbi_signal_event(ctx);
1915 usbi_mutex_unlock(&ctx->event_data_lock);
1918 /** \ingroup libusb_poll
1919 * Acquire the event waiters lock. This lock is designed to be obtained under
1920 * the situation where you want to be aware when events are completed, but
1921 * some other thread is event handling so calling libusb_handle_events() is not
1924 * You then obtain this lock, re-check that another thread is still handling
1925 * events, then call libusb_wait_for_event().
1927 * You only need to use this lock if you are developing an application
1928 * which calls poll() or select() on libusb's file descriptors directly,
1929 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1930 * If you stick to libusb's event handling loop functions (e.g.
1931 * libusb_handle_events()) then you do not need to be concerned with this
1934 * \param ctx the context to operate on, or NULL for the default context
1935 * \ref libusb_mtasync
1937 void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
1939 ctx = usbi_get_context(ctx);
1940 usbi_mutex_lock(&ctx->event_waiters_lock);
1943 /** \ingroup libusb_poll
1944 * Release the event waiters lock.
1945 * \param ctx the context to operate on, or NULL for the default context
1946 * \ref libusb_mtasync
1948 void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
1950 ctx = usbi_get_context(ctx);
1951 usbi_mutex_unlock(&ctx->event_waiters_lock);
1954 /** \ingroup libusb_poll
1955 * Wait for another thread to signal completion of an event. Must be called
1956 * with the event waiters lock held, see libusb_lock_event_waiters().
1958 * This function will block until any of the following conditions are met:
1959 * -# The timeout expires
1960 * -# A transfer completes
1961 * -# A thread releases the event handling lock through libusb_unlock_events()
1963 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1964 * the callback for the transfer has completed. Condition 3 is important
1965 * because it means that the thread that was previously handling events is no
1966 * longer doing so, so if any events are to complete, another thread needs to
1967 * step up and start event handling.
1969 * This function releases the event waiters lock before putting your thread
1970 * to sleep, and reacquires the lock as it is being woken up.
1972 * \param ctx the context to operate on, or NULL for the default context
1973 * \param tv maximum timeout for this blocking function. A NULL value
1974 * indicates unlimited timeout.
1975 * \returns 0 after a transfer completes or another thread stops event handling
1976 * \returns 1 if the timeout expired
1977 * \ref libusb_mtasync
1979 int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
1983 ctx = usbi_get_context(ctx);
1985 usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
1989 r = usbi_cond_timedwait(&ctx->event_waiters_cond,
1990 &ctx->event_waiters_lock, tv);
1995 return (r == ETIMEDOUT);
1998 static void handle_timeout(struct usbi_transfer *itransfer)
2000 struct libusb_transfer *transfer =
2001 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
2004 itransfer->timeout_flags |= USBI_TRANSFER_TIMEOUT_HANDLED;
2005 r = libusb_cancel_transfer(transfer);
2006 if (r == LIBUSB_SUCCESS)
2007 itransfer->timeout_flags |= USBI_TRANSFER_TIMED_OUT;
2009 usbi_warn(TRANSFER_CTX(transfer),
2010 "async cancel failed %d errno=%d", r, errno);
2013 static int handle_timeouts_locked(struct libusb_context *ctx)
2016 struct timespec systime_ts;
2017 struct timeval systime;
2018 struct usbi_transfer *itransfer;
2020 if (list_empty(&ctx->flying_transfers))
2023 /* get current time */
2024 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
2028 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
2030 /* iterate through flying transfers list, finding all transfers that
2031 * have expired timeouts */
2032 list_for_each_entry(itransfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2033 struct timeval *cur_tv = &itransfer->timeout;
2035 /* if we've reached transfers of infinite timeout, we're all done */
2036 if (!timerisset(cur_tv))
2039 /* ignore timeouts we've already handled */
2040 if (itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2043 /* if transfer has non-expired timeout, nothing more to do */
2044 if ((cur_tv->tv_sec > systime.tv_sec) ||
2045 (cur_tv->tv_sec == systime.tv_sec &&
2046 cur_tv->tv_usec > systime.tv_usec))
2049 /* otherwise, we've got an expired timeout to handle */
2050 handle_timeout(itransfer);
2055 static int handle_timeouts(struct libusb_context *ctx)
2059 ctx = usbi_get_context(ctx);
2060 usbi_mutex_lock(&ctx->flying_transfers_lock);
2061 r = handle_timeouts_locked(ctx);
2062 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2067 static int handle_timerfd_trigger(struct libusb_context *ctx)
2071 usbi_mutex_lock(&ctx->flying_transfers_lock);
2073 /* process the timeout that just happened */
2074 r = handle_timeouts_locked(ctx);
2078 /* arm for next timeout*/
2079 r = arm_timerfd_for_next_timeout(ctx);
2082 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2087 /* do the actual event handling. assumes that no other thread is concurrently
2088 * doing the same thing. */
2089 static int handle_events(struct libusb_context *ctx, struct timeval *tv)
2092 struct usbi_pollfd *ipollfd;
2093 usbi_nfds_t nfds = 0;
2094 usbi_nfds_t internal_nfds;
2095 struct pollfd *fds = NULL;
2098 /* prevent attempts to recursively handle events (e.g. calling into
2099 * libusb_handle_events() from within a hotplug or transfer callback) */
2100 usbi_mutex_lock(&ctx->event_data_lock);
2102 if (usbi_handling_events(ctx))
2103 r = LIBUSB_ERROR_BUSY;
2105 usbi_start_event_handling(ctx);
2106 usbi_mutex_unlock(&ctx->event_data_lock);
2111 /* there are certain fds that libusb uses internally, currently:
2116 * the backend will never need to attempt to handle events on these fds, so
2117 * we determine how many fds are in use internally for this context and when
2118 * handle_events() is called in the backend, the pollfd list and count will
2119 * be adjusted to skip over these internal fds */
2120 if (usbi_using_timerfd(ctx))
2125 /* only reallocate the poll fds when the list of poll fds has been modified
2126 * since the last poll, otherwise reuse them to save the additional overhead */
2127 usbi_mutex_lock(&ctx->event_data_lock);
2128 /* clean up removed poll fds */
2129 cleanup_removed_pollfds(ctx);
2130 if (ctx->event_flags & USBI_EVENT_POLLFDS_MODIFIED) {
2133 usbi_dbg("poll fds modified, reallocating");
2136 ctx->pollfds = NULL;
2138 /* sanity check - it is invalid for a context to have fewer than the
2139 * required internal fds (memory corruption?) */
2140 assert(ctx->pollfds_cnt >= internal_nfds);
2142 ctx->pollfds = calloc(ctx->pollfds_cnt, sizeof(*ctx->pollfds));
2143 if (!ctx->pollfds) {
2144 usbi_mutex_unlock(&ctx->event_data_lock);
2145 r = LIBUSB_ERROR_NO_MEM;
2149 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd) {
2150 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
2151 ctx->pollfds[i].fd = pollfd->fd;
2152 ctx->pollfds[i].events = pollfd->events;
2156 /* reset the flag now that we have the updated list */
2157 ctx->event_flags &= ~USBI_EVENT_POLLFDS_MODIFIED;
2159 /* if no further pending events, clear the event pipe so that we do
2160 * not immediately return from poll */
2161 if (!usbi_pending_events(ctx))
2162 usbi_clear_event(ctx);
2165 nfds = ctx->pollfds_cnt;
2166 usbi_mutex_unlock(&ctx->event_data_lock);
2168 timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000);
2170 /* round up to next millisecond */
2171 if (tv->tv_usec % 1000)
2174 usbi_dbg("poll() %d fds with timeout in %dms", (int)nfds, timeout_ms);
2175 r = usbi_poll(fds, nfds, timeout_ms);
2176 usbi_dbg("poll() returned %d", r);
2178 r = handle_timeouts(ctx);
2180 } else if (r == -1 && errno == EINTR) {
2181 r = LIBUSB_ERROR_INTERRUPTED;
2184 usbi_err(ctx, "poll failed, errno=%d", errno);
2185 r = LIBUSB_ERROR_IO;
2189 /* fds[0] is always the event pipe */
2190 if (fds[0].revents) {
2191 struct list_head hotplug_msgs;
2192 struct usbi_transfer *itransfer;
2193 int hotplug_cb_deregistered = 0;
2196 list_init(&hotplug_msgs);
2198 usbi_dbg("caught a fish on the event pipe");
2200 /* take the the event data lock while processing events */
2201 usbi_mutex_lock(&ctx->event_data_lock);
2203 /* check if someone added a new poll fd */
2204 if (ctx->event_flags & USBI_EVENT_POLLFDS_MODIFIED)
2205 usbi_dbg("someone updated the poll fds");
2207 if (ctx->event_flags & USBI_EVENT_USER_INTERRUPT) {
2208 usbi_dbg("someone purposely interrupted");
2209 ctx->event_flags &= ~USBI_EVENT_USER_INTERRUPT;
2212 if (ctx->event_flags & USBI_EVENT_HOTPLUG_CB_DEREGISTERED) {
2213 usbi_dbg("someone unregistered a hotplug cb");
2214 ctx->event_flags &= ~USBI_EVENT_HOTPLUG_CB_DEREGISTERED;
2215 hotplug_cb_deregistered = 1;
2218 /* check if someone is closing a device */
2219 if (ctx->device_close)
2220 usbi_dbg("someone is closing a device");
2222 /* check for any pending hotplug messages */
2223 if (!list_empty(&ctx->hotplug_msgs)) {
2224 usbi_dbg("hotplug message received");
2225 list_cut(&hotplug_msgs, &ctx->hotplug_msgs);
2228 /* complete any pending transfers */
2229 while (ret == 0 && !list_empty(&ctx->completed_transfers)) {
2230 itransfer = list_first_entry(&ctx->completed_transfers, struct usbi_transfer, completed_list);
2231 list_del(&itransfer->completed_list);
2232 usbi_mutex_unlock(&ctx->event_data_lock);
2233 ret = usbi_backend.handle_transfer_completion(itransfer);
2235 usbi_err(ctx, "backend handle_transfer_completion failed with error %d", ret);
2236 usbi_mutex_lock(&ctx->event_data_lock);
2239 /* if no further pending events, clear the event pipe */
2240 if (!usbi_pending_events(ctx))
2241 usbi_clear_event(ctx);
2243 usbi_mutex_unlock(&ctx->event_data_lock);
2245 if (hotplug_cb_deregistered)
2246 usbi_hotplug_deregister(ctx, 0);
2248 /* process the hotplug messages, if any */
2249 while (!list_empty(&hotplug_msgs)) {
2250 struct libusb_hotplug_message *message =
2251 list_first_entry(&hotplug_msgs, struct libusb_hotplug_message, list);
2253 usbi_hotplug_match(ctx, message->device, message->event);
2255 /* the device left, dereference the device */
2256 if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == message->event)
2257 libusb_unref_device(message->device);
2259 list_del(&message->list);
2264 /* return error code */
2274 /* on timerfd configurations, fds[1] is the timerfd */
2275 if (usbi_using_timerfd(ctx) && fds[1].revents) {
2276 /* timerfd indicates that a timeout has expired */
2278 usbi_dbg("timerfd triggered");
2280 ret = handle_timerfd_trigger(ctx);
2282 /* return error code */
2292 list_for_each_entry(ipollfd, &ctx->removed_ipollfds, list, struct usbi_pollfd) {
2295 for (n = internal_nfds ; n < nfds ; n++) {
2296 if (ipollfd->pollfd.fd == fds[n].fd) {
2297 /* pollfd was removed between the creation of the fd
2298 * array and here. remove any triggered revent as
2299 * it is no longer relevant */
2300 usbi_dbg("pollfd %d was removed. ignoring raised events",
2308 r = usbi_backend.handle_events(ctx, fds + internal_nfds, nfds - internal_nfds, r);
2310 usbi_err(ctx, "backend handle_events failed with error %d", r);
2313 usbi_end_event_handling(ctx);
2317 /* returns the smallest of:
2318 * 1. timeout of next URB
2319 * 2. user-supplied timeout
2320 * returns 1 if there is an already-expired timeout, otherwise returns 0
2323 static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
2324 struct timeval *out)
2326 struct timeval timeout;
2327 int r = libusb_get_next_timeout(ctx, &timeout);
2329 /* timeout already expired? */
2330 if (!timerisset(&timeout))
2333 /* choose the smallest of next URB timeout or user specified timeout */
2334 if (timercmp(&timeout, tv, <))
2344 /** \ingroup libusb_poll
2345 * Handle any pending events.
2347 * libusb determines "pending events" by checking if any timeouts have expired
2348 * and by checking the set of file descriptors for activity.
2350 * If a zero timeval is passed, this function will handle any already-pending
2351 * events and then immediately return in non-blocking style.
2353 * If a non-zero timeval is passed and no events are currently pending, this
2354 * function will block waiting for events to handle up until the specified
2355 * timeout. If an event arrives or a signal is raised, this function will
2358 * If the parameter completed is not NULL then <em>after obtaining the event
2359 * handling lock</em> this function will return immediately if the integer
2360 * pointed to is not 0. This allows for race free waiting for the completion
2361 * of a specific transfer.
2363 * \param ctx the context to operate on, or NULL for the default context
2364 * \param tv the maximum time to block waiting for events, or an all zero
2365 * timeval struct for non-blocking mode
2366 * \param completed pointer to completion integer to check, or NULL
2367 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2368 * \ref libusb_mtasync
2370 int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
2371 struct timeval *tv, int *completed)
2374 struct timeval poll_timeout;
2376 ctx = usbi_get_context(ctx);
2377 r = get_next_timeout(ctx, tv, &poll_timeout);
2379 /* timeout already expired */
2380 return handle_timeouts(ctx);
2384 if (libusb_try_lock_events(ctx) == 0) {
2385 if (completed == NULL || !*completed) {
2386 /* we obtained the event lock: do our own event handling */
2387 usbi_dbg("doing our own event handling");
2388 r = handle_events(ctx, &poll_timeout);
2390 libusb_unlock_events(ctx);
2394 /* another thread is doing event handling. wait for thread events that
2395 * notify event completion. */
2396 libusb_lock_event_waiters(ctx);
2398 if (completed && *completed)
2401 if (!libusb_event_handler_active(ctx)) {
2402 /* we hit a race: whoever was event handling earlier finished in the
2403 * time it took us to reach this point. try the cycle again. */
2404 libusb_unlock_event_waiters(ctx);
2405 usbi_dbg("event handler was active but went away, retrying");
2409 usbi_dbg("another thread is doing event handling");
2410 r = libusb_wait_for_event(ctx, &poll_timeout);
2413 libusb_unlock_event_waiters(ctx);
2418 return handle_timeouts(ctx);
2423 /** \ingroup libusb_poll
2424 * Handle any pending events
2426 * Like libusb_handle_events_timeout_completed(), but without the completed
2427 * parameter, calling this function is equivalent to calling
2428 * libusb_handle_events_timeout_completed() with a NULL completed parameter.
2430 * This function is kept primarily for backwards compatibility.
2431 * All new code should call libusb_handle_events_completed() or
2432 * libusb_handle_events_timeout_completed() to avoid race conditions.
2434 * \param ctx the context to operate on, or NULL for the default context
2435 * \param tv the maximum time to block waiting for events, or an all zero
2436 * timeval struct for non-blocking mode
2437 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2439 int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
2442 return libusb_handle_events_timeout_completed(ctx, tv, NULL);
2445 /** \ingroup libusb_poll
2446 * Handle any pending events in blocking mode. There is currently a timeout
2447 * hardcoded at 60 seconds but we plan to make it unlimited in future. For
2448 * finer control over whether this function is blocking or non-blocking, or
2449 * for control over the timeout, use libusb_handle_events_timeout_completed()
2452 * This function is kept primarily for backwards compatibility.
2453 * All new code should call libusb_handle_events_completed() or
2454 * libusb_handle_events_timeout_completed() to avoid race conditions.
2456 * \param ctx the context to operate on, or NULL for the default context
2457 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2459 int API_EXPORTED libusb_handle_events(libusb_context *ctx)
2464 return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
2467 /** \ingroup libusb_poll
2468 * Handle any pending events in blocking mode.
2470 * Like libusb_handle_events(), with the addition of a completed parameter
2471 * to allow for race free waiting for the completion of a specific transfer.
2473 * See libusb_handle_events_timeout_completed() for details on the completed
2476 * \param ctx the context to operate on, or NULL for the default context
2477 * \param completed pointer to completion integer to check, or NULL
2478 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2479 * \ref libusb_mtasync
2481 int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
2487 return libusb_handle_events_timeout_completed(ctx, &tv, completed);
2490 /** \ingroup libusb_poll
2491 * Handle any pending events by polling file descriptors, without checking if
2492 * any other threads are already doing so. Must be called with the event lock
2493 * held, see libusb_lock_events().
2495 * This function is designed to be called under the situation where you have
2496 * taken the event lock and are calling poll()/select() directly on libusb's
2497 * file descriptors (as opposed to using libusb_handle_events() or similar).
2498 * You detect events on libusb's descriptors, so you then call this function
2499 * with a zero timeout value (while still holding the event lock).
2501 * \param ctx the context to operate on, or NULL for the default context
2502 * \param tv the maximum time to block waiting for events, or zero for
2504 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2505 * \ref libusb_mtasync
2507 int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
2511 struct timeval poll_timeout;
2513 ctx = usbi_get_context(ctx);
2514 r = get_next_timeout(ctx, tv, &poll_timeout);
2516 /* timeout already expired */
2517 return handle_timeouts(ctx);
2520 return handle_events(ctx, &poll_timeout);
2523 /** \ingroup libusb_poll
2524 * Determines whether your application must apply special timing considerations
2525 * when monitoring libusb's file descriptors.
2527 * This function is only useful for applications which retrieve and poll
2528 * libusb's file descriptors in their own main loop (\ref libusb_pollmain).
2530 * Ordinarily, libusb's event handler needs to be called into at specific
2531 * moments in time (in addition to times when there is activity on the file
2532 * descriptor set). The usual approach is to use libusb_get_next_timeout()
2533 * to learn about when the next timeout occurs, and to adjust your
2534 * poll()/select() timeout accordingly so that you can make a call into the
2535 * library at that time.
2537 * Some platforms supported by libusb do not come with this baggage - any
2538 * events relevant to timing will be represented by activity on the file
2539 * descriptor set, and libusb_get_next_timeout() will always return 0.
2540 * This function allows you to detect whether you are running on such a
2545 * \param ctx the context to operate on, or NULL for the default context
2546 * \returns 0 if you must call into libusb at times determined by
2547 * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
2548 * or through regular activity on the file descriptors.
2549 * \ref libusb_pollmain "Polling libusb file descriptors for event handling"
2551 int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
2554 ctx = usbi_get_context(ctx);
2555 return usbi_using_timerfd(ctx);
2562 /** \ingroup libusb_poll
2563 * Determine the next internal timeout that libusb needs to handle. You only
2564 * need to use this function if you are calling poll() or select() or similar
2565 * on libusb's file descriptors yourself - you do not need to use it if you
2566 * are calling libusb_handle_events() or a variant directly.
2568 * You should call this function in your main loop in order to determine how
2569 * long to wait for select() or poll() to return results. libusb needs to be
2570 * called into at this timeout, so you should use it as an upper bound on
2571 * your select() or poll() call.
2573 * When the timeout has expired, call into libusb_handle_events_timeout()
2574 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
2576 * This function may return 1 (success) and an all-zero timeval. If this is
2577 * the case, it indicates that libusb has a timeout that has already expired
2578 * so you should call libusb_handle_events_timeout() or similar immediately.
2579 * A return code of 0 indicates that there are no pending timeouts.
2581 * On some platforms, this function will always returns 0 (no pending
2582 * timeouts). See \ref polltime.
2584 * \param ctx the context to operate on, or NULL for the default context
2585 * \param tv output location for a relative time against the current
2586 * clock in which libusb must be called into in order to process timeout events
2587 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
2588 * or LIBUSB_ERROR_OTHER on failure
2590 int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
2593 struct usbi_transfer *itransfer;
2594 struct timespec cur_ts;
2595 struct timeval cur_tv;
2596 struct timeval next_timeout = { 0, 0 };
2599 ctx = usbi_get_context(ctx);
2600 if (usbi_using_timerfd(ctx))
2603 usbi_mutex_lock(&ctx->flying_transfers_lock);
2604 if (list_empty(&ctx->flying_transfers)) {
2605 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2606 usbi_dbg("no URBs, no timeout!");
2610 /* find next transfer which hasn't already been processed as timed out */
2611 list_for_each_entry(itransfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2612 if (itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2615 /* if we've reached transfers of infinte timeout, we're done looking */
2616 if (!timerisset(&itransfer->timeout))
2619 next_timeout = itransfer->timeout;
2622 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2624 if (!timerisset(&next_timeout)) {
2625 usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
2629 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
2631 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2634 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
2636 if (!timercmp(&cur_tv, &next_timeout, <)) {
2637 usbi_dbg("first timeout already expired");
2640 timersub(&next_timeout, &cur_tv, tv);
2641 usbi_dbg("next timeout in %ld.%06lds", (long)tv->tv_sec, (long)tv->tv_usec);
2647 /** \ingroup libusb_poll
2648 * Register notification functions for file descriptor additions/removals.
2649 * These functions will be invoked for every new or removed file descriptor
2650 * that libusb uses as an event source.
2652 * To remove notifiers, pass NULL values for the function pointers.
2654 * Note that file descriptors may have been added even before you register
2655 * these notifiers (e.g. at libusb_init() time).
2657 * Additionally, note that the removal notifier may be called during
2658 * libusb_exit() (e.g. when it is closing file descriptors that were opened
2659 * and added to the poll set at libusb_init() time). If you don't want this,
2660 * remove the notifiers immediately before calling libusb_exit().
2662 * \param ctx the context to operate on, or NULL for the default context
2663 * \param added_cb pointer to function for addition notifications
2664 * \param removed_cb pointer to function for removal notifications
2665 * \param user_data User data to be passed back to callbacks (useful for
2666 * passing context information)
2668 void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
2669 libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
2672 ctx = usbi_get_context(ctx);
2673 ctx->fd_added_cb = added_cb;
2674 ctx->fd_removed_cb = removed_cb;
2675 ctx->fd_cb_user_data = user_data;
2679 * Interrupt the iteration of the event handling thread, so that it picks
2680 * up the fd change. Callers of this function must hold the event_data_lock.
2682 static void usbi_fd_notification(struct libusb_context *ctx)
2686 /* Record that there is a new poll fd.
2687 * Only signal an event if there are no prior pending events. */
2688 pending_events = usbi_pending_events(ctx);
2689 ctx->event_flags |= USBI_EVENT_POLLFDS_MODIFIED;
2690 if (!pending_events)
2691 usbi_signal_event(ctx);
2694 /* Add a file descriptor to the list of file descriptors to be monitored.
2695 * events should be specified as a bitmask of events passed to poll(), e.g.
2696 * POLLIN and/or POLLOUT. */
2697 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
2699 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
2701 return LIBUSB_ERROR_NO_MEM;
2703 usbi_dbg("add fd %d events %d", fd, events);
2704 ipollfd->pollfd.fd = fd;
2705 ipollfd->pollfd.events = events;
2706 usbi_mutex_lock(&ctx->event_data_lock);
2707 list_add_tail(&ipollfd->list, &ctx->ipollfds);
2709 usbi_fd_notification(ctx);
2710 usbi_mutex_unlock(&ctx->event_data_lock);
2712 if (ctx->fd_added_cb)
2713 ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
2717 /* Remove a file descriptor from the list of file descriptors to be polled. */
2718 void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
2720 struct usbi_pollfd *ipollfd;
2723 usbi_dbg("remove fd %d", fd);
2724 usbi_mutex_lock(&ctx->event_data_lock);
2725 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd)
2726 if (ipollfd->pollfd.fd == fd) {
2732 usbi_dbg("couldn't find fd %d to remove", fd);
2733 usbi_mutex_unlock(&ctx->event_data_lock);
2737 list_del(&ipollfd->list);
2738 list_add_tail(&ipollfd->list, &ctx->removed_ipollfds);
2740 usbi_fd_notification(ctx);
2741 usbi_mutex_unlock(&ctx->event_data_lock);
2743 if (ctx->fd_removed_cb)
2744 ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
2747 /** \ingroup libusb_poll
2748 * Retrieve a list of file descriptors that should be polled by your main loop
2749 * as libusb event sources.
2751 * The returned list is NULL-terminated and should be freed with libusb_free_pollfds()
2752 * when done. The actual list contents must not be touched.
2754 * As file descriptors are a Unix-specific concept, this function is not
2755 * available on Windows and will always return NULL.
2757 * \param ctx the context to operate on, or NULL for the default context
2758 * \returns a NULL-terminated list of libusb_pollfd structures
2759 * \returns NULL on error
2760 * \returns NULL on platforms where the functionality is not available
2763 const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
2764 libusb_context *ctx)
2767 struct libusb_pollfd **ret = NULL;
2768 struct usbi_pollfd *ipollfd;
2771 ctx = usbi_get_context(ctx);
2773 usbi_mutex_lock(&ctx->event_data_lock);
2775 ret = calloc(ctx->pollfds_cnt + 1, sizeof(struct libusb_pollfd *));
2779 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd)
2780 ret[i++] = (struct libusb_pollfd *) ipollfd;
2781 ret[ctx->pollfds_cnt] = NULL;
2784 usbi_mutex_unlock(&ctx->event_data_lock);
2785 return (const struct libusb_pollfd **) ret;
2787 usbi_err(ctx, "external polling of libusb's internal descriptors "\
2788 "is not yet supported on Windows platforms");
2793 /** \ingroup libusb_poll
2794 * Free a list of libusb_pollfd structures. This should be called for all
2795 * pollfd lists allocated with libusb_get_pollfds().
2797 * Since version 1.0.20, \ref LIBUSB_API_VERSION >= 0x01000104
2799 * It is legal to call this function with a NULL pollfd list. In this case,
2800 * the function will simply do nothing.
2802 * \param pollfds the list of libusb_pollfd structures to free
2804 void API_EXPORTED libusb_free_pollfds(const struct libusb_pollfd **pollfds)
2806 free((void *)pollfds);
2809 /* Backends may call this from handle_events to report disconnection of a
2810 * device. This function ensures transfers get cancelled appropriately.
2811 * Callers of this function must hold the events_lock.
2813 void usbi_handle_disconnect(struct libusb_device_handle *dev_handle)
2815 struct usbi_transfer *cur;
2816 struct usbi_transfer *to_cancel;
2818 usbi_dbg("device %d.%d",
2819 dev_handle->dev->bus_number, dev_handle->dev->device_address);
2821 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
2824 * when we find a transfer for this device on the list, there are two
2825 * possible scenarios:
2826 * 1. the transfer is currently in-flight, in which case we terminate the
2828 * 2. the transfer has been added to the flying transfer list by
2829 * libusb_submit_transfer, has failed to submit and
2830 * libusb_submit_transfer is waiting for us to release the
2831 * flying_transfers_lock to remove it, so we ignore it
2836 usbi_mutex_lock(&HANDLE_CTX(dev_handle)->flying_transfers_lock);
2837 list_for_each_entry(cur, &HANDLE_CTX(dev_handle)->flying_transfers, list, struct usbi_transfer)
2838 if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == dev_handle) {
2839 usbi_mutex_lock(&cur->lock);
2840 if (cur->state_flags & USBI_TRANSFER_IN_FLIGHT)
2842 usbi_mutex_unlock(&cur->lock);
2847 usbi_mutex_unlock(&HANDLE_CTX(dev_handle)->flying_transfers_lock);
2852 usbi_dbg("cancelling transfer %p from disconnect",
2853 USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel));
2855 usbi_mutex_lock(&to_cancel->lock);
2856 usbi_backend.clear_transfer_priv(to_cancel);
2857 usbi_mutex_unlock(&to_cancel->lock);
2858 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);