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>
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
30 #ifdef HAVE_SYS_TIME_H
33 #ifdef USBI_TIMERFD_AVAILABLE
35 #include <sys/timerfd.h>
42 * \page libusb_io Synchronous and asynchronous device I/O
44 * \section io_intro Introduction
46 * If you're using libusb in your application, you're probably wanting to
47 * perform I/O with devices - you want to perform USB data transfers.
49 * libusb offers two separate interfaces for device I/O. This page aims to
50 * introduce the two in order to help you decide which one is more suitable
51 * for your application. You can also choose to use both interfaces in your
52 * application by considering each transfer on a case-by-case basis.
54 * Once you have read through the following discussion, you should consult the
55 * detailed API documentation pages for the details:
56 * - \ref libusb_syncio
57 * - \ref libusb_asyncio
59 * \section theory Transfers at a logical level
61 * At a logical level, USB transfers typically happen in two parts. For
62 * example, when reading data from a endpoint:
63 * -# A request for data is sent to the device
64 * -# Some time later, the incoming data is received by the host
66 * or when writing data to an endpoint:
68 * -# The data is sent to the device
69 * -# Some time later, the host receives acknowledgement from the device that
70 * the data has been transferred.
72 * There may be an indefinite delay between the two steps. Consider a
73 * fictional USB input device with a button that the user can press. In order
74 * to determine when the button is pressed, you would likely submit a request
75 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
76 * Data will arrive when the button is pressed by the user, which is
77 * potentially hours later.
79 * libusb offers both a synchronous and an asynchronous interface to performing
80 * USB transfers. The main difference is that the synchronous interface
81 * combines both steps indicated above into a single function call, whereas
82 * the asynchronous interface separates them.
84 * \section sync The synchronous interface
86 * The synchronous I/O interface allows you to perform a USB transfer with
87 * a single function call. When the function call returns, the transfer has
88 * completed and you can parse the results.
90 * If you have used the libusb-0.1 before, this I/O style will seem familar to
91 * you. libusb-0.1 only offered a synchronous interface.
93 * In our input device example, to read button presses you might write code
94 * in the following style:
96 unsigned char data[4];
98 int r = libusb_bulk_transfer(dev_handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
99 if (r == 0 && actual_length == sizeof(data)) {
100 // results of the transaction can now be found in the data buffer
101 // parse them here and report button press
107 * The main advantage of this model is simplicity: you did everything with
108 * a single simple function call.
110 * However, this interface has its limitations. Your application will sleep
111 * inside libusb_bulk_transfer() until the transaction has completed. If it
112 * takes the user 3 hours to press the button, your application will be
113 * sleeping for that long. Execution will be tied up inside the library -
114 * the entire thread will be useless for that duration.
116 * Another issue is that by tieing up the thread with that single transaction
117 * there is no possibility of performing I/O with multiple endpoints and/or
118 * multiple devices simultaneously, unless you resort to creating one thread
121 * Additionally, there is no opportunity to cancel the transfer after the
122 * request has been submitted.
124 * For details on how to use the synchronous API, see the
125 * \ref libusb_syncio "synchronous I/O API documentation" pages.
127 * \section async The asynchronous interface
129 * Asynchronous I/O is the most significant new feature in libusb-1.0.
130 * Although it is a more complex interface, it solves all the issues detailed
133 * Instead of providing which functions that block until the I/O has complete,
134 * libusb's asynchronous interface presents non-blocking functions which
135 * begin a transfer and then return immediately. Your application passes a
136 * callback function pointer to this non-blocking function, which libusb will
137 * call with the results of the transaction when it has completed.
139 * Transfers which have been submitted through the non-blocking functions
140 * can be cancelled with a separate function call.
142 * The non-blocking nature of this interface allows you to be simultaneously
143 * performing I/O to multiple endpoints on multiple devices, without having
146 * This added flexibility does come with some complications though:
147 * - In the interest of being a lightweight library, libusb does not create
148 * threads and can only operate when your application is calling into it. Your
149 * application must call into libusb from it's main loop when events are ready
150 * to be handled, or you must use some other scheme to allow libusb to
151 * undertake whatever work needs to be done.
152 * - libusb also needs to be called into at certain fixed points in time in
153 * order to accurately handle transfer timeouts.
154 * - Memory handling becomes more complex. You cannot use stack memory unless
155 * the function with that stack is guaranteed not to return until the transfer
156 * callback has finished executing.
157 * - You generally lose some linearity from your code flow because submitting
158 * the transfer request is done in a separate function from where the transfer
159 * results are handled. This becomes particularly obvious when you want to
160 * submit a second transfer based on the results of an earlier transfer.
162 * Internally, libusb's synchronous interface is expressed in terms of function
163 * calls to the asynchronous interface.
165 * For details on how to use the asynchronous API, see the
166 * \ref libusb_asyncio "asynchronous I/O API" documentation pages.
171 * \page libusb_packetoverflow Packets and overflows
173 * \section packets Packet abstraction
175 * The USB specifications describe how data is transmitted in packets, with
176 * constraints on packet size defined by endpoint descriptors. The host must
177 * not send data payloads larger than the endpoint's maximum packet size.
179 * libusb and the underlying OS abstract out the packet concept, allowing you
180 * to request transfers of any size. Internally, the request will be divided
181 * up into correctly-sized packets. You do not have to be concerned with
182 * packet sizes, but there is one exception when considering overflows.
184 * \section overflow Bulk/interrupt transfer overflows
186 * When requesting data on a bulk endpoint, libusb requires you to supply a
187 * buffer and the maximum number of bytes of data that libusb can put in that
188 * buffer. However, the size of the buffer is not communicated to the device -
189 * the device is just asked to send any amount of data.
191 * There is no problem if the device sends an amount of data that is less than
192 * or equal to the buffer size. libusb reports this condition to you through
193 * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
196 * Problems may occur if the device attempts to send more data than can fit in
197 * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
198 * other behaviour is largely undefined: actual_length may or may not be
199 * accurate, the chunk of data that can fit in the buffer (before overflow)
200 * may or may not have been transferred.
202 * Overflows are nasty, but can be avoided. Even though you were told to
203 * ignore packets above, think about the lower level details: each transfer is
204 * split into packets (typically small, with a maximum size of 512 bytes).
205 * Overflows can only happen if the final packet in an incoming data transfer
206 * is smaller than the actual packet that the device wants to transfer.
207 * Therefore, you will never see an overflow if your transfer buffer size is a
208 * multiple of the endpoint's packet size: the final packet will either
209 * fill up completely or will be only partially filled.
213 * @defgroup libusb_asyncio Asynchronous device I/O
215 * This page details libusb's asynchronous (non-blocking) API for USB device
216 * I/O. This interface is very powerful but is also quite complex - you will
217 * need to read this page carefully to understand the necessary considerations
218 * and issues surrounding use of this interface. Simplistic applications
219 * may wish to consider the \ref libusb_syncio "synchronous I/O API" instead.
221 * The asynchronous interface is built around the idea of separating transfer
222 * submission and handling of transfer completion (the synchronous model
223 * combines both of these into one). There may be a long delay between
224 * submission and completion, however the asynchronous submission function
225 * is non-blocking so will return control to your application during that
226 * potentially long delay.
228 * \section asyncabstraction Transfer abstraction
230 * For the asynchronous I/O, libusb implements the concept of a generic
231 * transfer entity for all types of I/O (control, bulk, interrupt,
232 * isochronous). The generic transfer object must be treated slightly
233 * differently depending on which type of I/O you are performing with it.
235 * This is represented by the public libusb_transfer structure type.
237 * \section asynctrf Asynchronous transfers
239 * We can view asynchronous I/O as a 5 step process:
240 * -# <b>Allocation</b>: allocate a libusb_transfer
241 * -# <b>Filling</b>: populate the libusb_transfer instance with information
242 * about the transfer you wish to perform
243 * -# <b>Submission</b>: ask libusb to submit the transfer
244 * -# <b>Completion handling</b>: examine transfer results in the
245 * libusb_transfer structure
246 * -# <b>Deallocation</b>: clean up resources
249 * \subsection asyncalloc Allocation
251 * This step involves allocating memory for a USB transfer. This is the
252 * generic transfer object mentioned above. At this stage, the transfer
253 * is "blank" with no details about what type of I/O it will be used for.
255 * Allocation is done with the libusb_alloc_transfer() function. You must use
256 * this function rather than allocating your own transfers.
258 * \subsection asyncfill Filling
260 * This step is where you take a previously allocated transfer and fill it
261 * with information to determine the message type and direction, data buffer,
262 * callback function, etc.
264 * You can either fill the required fields yourself or you can use the
265 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
266 * and libusb_fill_interrupt_transfer().
268 * \subsection asyncsubmit Submission
270 * When you have allocated a transfer and filled it, you can submit it using
271 * libusb_submit_transfer(). This function returns immediately but can be
272 * regarded as firing off the I/O request in the background.
274 * \subsection asynccomplete Completion handling
276 * After a transfer has been submitted, one of four things can happen to it:
278 * - The transfer completes (i.e. some data was transferred)
279 * - The transfer has a timeout and the timeout expires before all data is
281 * - The transfer fails due to an error
282 * - The transfer is cancelled
284 * Each of these will cause the user-specified transfer callback function to
285 * be invoked. It is up to the callback function to determine which of the
286 * above actually happened and to act accordingly.
288 * The user-specified callback is passed a pointer to the libusb_transfer
289 * structure which was used to setup and submit the transfer. At completion
290 * time, libusb has populated this structure with results of the transfer:
291 * success or failure reason, number of bytes of data transferred, etc. See
292 * the libusb_transfer structure documentation for more information.
294 * <b>Important Note</b>: The user-specified callback is called from an event
295 * handling context. It is therefore important that no calls are made into
296 * libusb that will attempt to perform any event handling. Examples of such
297 * functions are any listed in the \ref libusb_syncio "synchronous API" and any of
298 * the blocking functions that retrieve \ref libusb_desc "USB descriptors".
300 * \subsection Deallocation
302 * When a transfer has completed (i.e. the callback function has been invoked),
303 * you are advised to free the transfer (unless you wish to resubmit it, see
304 * below). Transfers are deallocated with libusb_free_transfer().
306 * It is undefined behaviour to free a transfer which has not completed.
308 * \section asyncresubmit Resubmission
310 * You may be wondering why allocation, filling, and submission are all
311 * separated above where they could reasonably be combined into a single
314 * The reason for separation is to allow you to resubmit transfers without
315 * having to allocate new ones every time. This is especially useful for
316 * common situations dealing with interrupt endpoints - you allocate one
317 * transfer, fill and submit it, and when it returns with results you just
318 * resubmit it for the next interrupt.
320 * \section asynccancel Cancellation
322 * Another advantage of using the asynchronous interface is that you have
323 * the ability to cancel transfers which have not yet completed. This is
324 * done by calling the libusb_cancel_transfer() function.
326 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
327 * cancellation actually completes, the transfer's callback function will
328 * be invoked, and the callback function should check the transfer status to
329 * determine that it was cancelled.
331 * Freeing the transfer after it has been cancelled but before cancellation
332 * has completed will result in undefined behaviour.
334 * When a transfer is cancelled, some of the data may have been transferred.
335 * libusb will communicate this to you in the transfer callback. Do not assume
336 * that no data was transferred.
338 * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
340 * If your device does not have predictable transfer sizes (or it misbehaves),
341 * your application may submit a request for data on an IN endpoint which is
342 * smaller than the data that the device wishes to send. In some circumstances
343 * this will cause an overflow, which is a nasty condition to deal with. See
344 * the \ref libusb_packetoverflow page for discussion.
346 * \section asyncctrl Considerations for control transfers
348 * The <tt>libusb_transfer</tt> structure is generic and hence does not
349 * include specific fields for the control-specific setup packet structure.
351 * In order to perform a control transfer, you must place the 8-byte setup
352 * packet at the start of the data buffer. To simplify this, you could
353 * cast the buffer pointer to type struct libusb_control_setup, or you can
354 * use the helper function libusb_fill_control_setup().
356 * The wLength field placed in the setup packet must be the length you would
357 * expect to be sent in the setup packet: the length of the payload that
358 * follows (or the expected maximum number of bytes to receive). However,
359 * the length field of the libusb_transfer object must be the length of
360 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
361 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
363 * If you use the helper functions, this is simplified for you:
364 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
365 * data you are sending/requesting.
366 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
367 * request size as the wLength value (i.e. do not include the extra space you
368 * allocated for the control setup).
369 * -# If this is a host-to-device transfer, place the data to be transferred
370 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
371 * -# Call libusb_fill_control_transfer() to associate the data buffer with
372 * the transfer (and to set the remaining details such as callback and timeout).
373 * - Note that there is no parameter to set the length field of the transfer.
374 * The length is automatically inferred from the wLength field of the setup
376 * -# Submit the transfer.
378 * The multi-byte control setup fields (wValue, wIndex and wLength) must
379 * be given in little-endian byte order (the endianness of the USB bus).
380 * Endianness conversion is transparently handled by
381 * libusb_fill_control_setup() which is documented to accept host-endian
384 * Further considerations are needed when handling transfer completion in
385 * your callback function:
386 * - As you might expect, the setup packet will still be sitting at the start
387 * of the data buffer.
388 * - If this was a device-to-host transfer, the received data will be sitting
389 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
390 * - The actual_length field of the transfer structure is relative to the
391 * wLength of the setup packet, rather than the size of the data buffer. So,
392 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
393 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
394 * transferred in entirity.
396 * To simplify parsing of setup packets and obtaining the data from the
397 * correct offset, you may wish to use the libusb_control_transfer_get_data()
398 * and libusb_control_transfer_get_setup() functions within your transfer
401 * Even though control endpoints do not halt, a completed control transfer
402 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
403 * request was not supported.
405 * \section asyncintr Considerations for interrupt transfers
407 * All interrupt transfers are performed using the polling interval presented
408 * by the bInterval value of the endpoint descriptor.
410 * \section asynciso Considerations for isochronous transfers
412 * Isochronous transfers are more complicated than transfers to
413 * non-isochronous endpoints.
415 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
416 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
418 * During filling, set \ref libusb_transfer::type "type" to
419 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
420 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
421 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
422 * or equal to the number of packets you requested during allocation.
423 * libusb_alloc_transfer() does not set either of these fields for you, given
424 * that you might not even use the transfer on an isochronous endpoint.
426 * Next, populate the length field for the first num_iso_packets entries in
427 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
428 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
429 * packet length is determined by the wMaxPacketSize field in the endpoint
431 * Two functions can help you here:
433 * - libusb_get_max_iso_packet_size() is an easy way to determine the max
434 * packet size for an isochronous endpoint. Note that the maximum packet
435 * size is actually the maximum number of bytes that can be transmitted in
436 * a single microframe, therefore this function multiplies the maximum number
437 * of bytes per transaction by the number of transaction opportunities per
439 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
440 * within a transfer, which is usually what you want.
442 * For outgoing transfers, you'll obviously fill the buffer and populate the
443 * packet descriptors in hope that all the data gets transferred. For incoming
444 * transfers, you must ensure the buffer has sufficient capacity for
445 * the situation where all packets transfer the full amount of requested data.
447 * Completion handling requires some extra consideration. The
448 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
449 * is meaningless and should not be examined; instead you must refer to the
450 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
451 * each individual packet.
453 * The \ref libusb_transfer::status "status" field of the transfer is also a
455 * - If the packets were submitted and the isochronous data microframes
456 * completed normally, status will have value
457 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
458 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
459 * delays are not counted as transfer errors; the transfer.status field may
460 * indicate COMPLETED even if some or all of the packets failed. Refer to
461 * the \ref libusb_iso_packet_descriptor::status "status" field of each
462 * individual packet to determine packet failures.
463 * - The status field will have value
464 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
465 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
466 * - Other transfer status codes occur with normal behaviour.
468 * The data for each packet will be found at an offset into the buffer that
469 * can be calculated as if each prior packet completed in full. The
470 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
471 * functions may help you here.
473 * <b>Note</b>: Some operating systems (e.g. Linux) may impose limits on the
474 * length of individual isochronous packets and/or the total length of the
475 * isochronous transfer. Such limits can be difficult for libusb to detect,
476 * so the library will simply try and submit the transfer as set up by you.
477 * If the transfer fails to submit because it is too large,
478 * libusb_submit_transfer() will return
479 * \ref libusb_error::LIBUSB_ERROR_INVALID_PARAM "LIBUSB_ERROR_INVALID_PARAM".
481 * \section asyncmem Memory caveats
483 * In most circumstances, it is not safe to use stack memory for transfer
484 * buffers. This is because the function that fired off the asynchronous
485 * transfer may return before libusb has finished using the buffer, and when
486 * the function returns it's stack gets destroyed. This is true for both
487 * host-to-device and device-to-host transfers.
489 * The only case in which it is safe to use stack memory is where you can
490 * guarantee that the function owning the stack space for the buffer does not
491 * return until after the transfer's callback function has completed. In every
492 * other case, you need to use heap memory instead.
494 * \section asyncflags Fine control
496 * Through using this asynchronous interface, you may find yourself repeating
497 * a few simple operations many times. You can apply a bitwise OR of certain
498 * flags to a transfer to simplify certain things:
499 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
500 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
501 * less than the requested amount of data being marked with status
502 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
503 * (they would normally be regarded as COMPLETED)
504 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
505 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
506 * buffer when freeing the transfer.
507 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
508 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
509 * transfer after the transfer callback returns.
511 * \section asyncevent Event handling
513 * An asynchronous model requires that libusb perform work at various
514 * points in time - namely processing the results of previously-submitted
515 * transfers and invoking the user-supplied callback function.
517 * This gives rise to the libusb_handle_events() function which your
518 * application must call into when libusb has work do to. This gives libusb
519 * the opportunity to reap pending transfers, invoke callbacks, etc.
521 * There are 2 different approaches to dealing with libusb_handle_events:
523 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
525 * -# Integrate libusb with your application's main event loop. libusb
526 * exposes a set of file descriptors which allow you to do this.
528 * The first approach has the big advantage that it will also work on Windows
529 * were libusb' poll API for select / poll integration is not available. So
530 * if you want to support Windows and use the async API, you must use this
531 * approach, see the \ref eventthread "Using an event handling thread" section
534 * If you prefer a single threaded approach with a single central event loop,
535 * see the \ref libusb_poll "polling and timing" section for how to integrate libusb
536 * into your application's main event loop.
538 * \section eventthread Using an event handling thread
540 * Lets begin with stating the obvious: If you're going to use a separate
541 * thread for libusb event handling, your callback functions MUST be
544 * Other then that doing event handling from a separate thread, is mostly
545 * simple. You can use an event thread function as follows:
547 void *event_thread_func(void *ctx)
549 while (event_thread_run)
550 libusb_handle_events(ctx);
556 * There is one caveat though, stopping this thread requires setting the
557 * event_thread_run variable to 0, and after that libusb_handle_events() needs
558 * to return control to event_thread_func. But unless some event happens,
559 * libusb_handle_events() will not return.
561 * There are 2 different ways of dealing with this, depending on if your
562 * application uses libusb' \ref libusb_hotplug "hotplug" support or not.
564 * Applications which do not use hotplug support, should not start the event
565 * thread until after their first call to libusb_open(), and should stop the
566 * thread when closing the last open device as follows:
568 void my_close_handle(libusb_device_handle *dev_handle)
571 event_thread_run = 0;
573 libusb_close(dev_handle); // This wakes up libusb_handle_events()
576 pthread_join(event_thread);
582 * Applications using hotplug support should start the thread at program init,
583 * after having successfully called libusb_hotplug_register_callback(), and
584 * should stop the thread at program exit as follows:
586 void my_libusb_exit(void)
588 event_thread_run = 0;
589 libusb_hotplug_deregister_callback(ctx, hotplug_cb_handle); // This wakes up libusb_handle_events()
590 pthread_join(event_thread);
597 * @defgroup libusb_poll Polling and timing
599 * This page documents libusb's functions for polling events and timing.
600 * These functions are only necessary for users of the
601 * \ref libusb_asyncio "asynchronous API". If you are only using the simpler
602 * \ref libusb_syncio "synchronous API" then you do not need to ever call these
605 * The justification for the functionality described here has already been
606 * discussed in the \ref asyncevent "event handling" section of the
607 * asynchronous API documentation. In summary, libusb does not create internal
608 * threads for event processing and hence relies on your application calling
609 * into libusb at certain points in time so that pending events can be handled.
611 * Your main loop is probably already calling poll() or select() or a
612 * variant on a set of file descriptors for other event sources (e.g. keyboard
613 * button presses, mouse movements, network sockets, etc). You then add
614 * libusb's file descriptors to your poll()/select() calls, and when activity
615 * is detected on such descriptors you know it is time to call
616 * libusb_handle_events().
618 * There is one final event handling complication. libusb supports
619 * asynchronous transfers which time out after a specified time period.
621 * On some platforms a timerfd is used, so the timeout handling is just another
622 * fd, on other platforms this requires that libusb is called into at or after
623 * the timeout to handle it. So, in addition to considering libusb's file
624 * descriptors in your main event loop, you must also consider that libusb
625 * sometimes needs to be called into at fixed points in time even when there
626 * is no file descriptor activity, see \ref polltime details.
628 * In order to know precisely when libusb needs to be called into, libusb
629 * offers you a set of pollable file descriptors and information about when
630 * the next timeout expires.
632 * If you are using the asynchronous I/O API, you must take one of the two
633 * following options, otherwise your I/O will not complete.
635 * \section pollsimple The simple option
637 * If your application revolves solely around libusb and does not need to
638 * handle other event sources, you can have a program structure as follows:
641 // find and open device
642 // maybe fire off some initial async I/O
644 while (user_has_not_requested_exit)
645 libusb_handle_events(ctx);
650 * With such a simple main loop, you do not have to worry about managing
651 * sets of file descriptors or handling timeouts. libusb_handle_events() will
652 * handle those details internally.
654 * \section libusb_pollmain The more advanced option
656 * \note This functionality is currently only available on Unix-like platforms.
657 * On Windows, libusb_get_pollfds() simply returns NULL. Applications which
658 * want to support Windows are advised to use an \ref eventthread
659 * "event handling thread" instead.
661 * In more advanced applications, you will already have a main loop which
662 * is monitoring other event sources: network sockets, X11 events, mouse
663 * movements, etc. Through exposing a set of file descriptors, libusb is
664 * designed to cleanly integrate into such main loops.
666 * In addition to polling file descriptors for the other event sources, you
667 * take a set of file descriptors from libusb and monitor those too. When you
668 * detect activity on libusb's file descriptors, you call
669 * libusb_handle_events_timeout() in non-blocking mode.
671 * What's more, libusb may also need to handle events at specific moments in
672 * time. No file descriptor activity is generated at these times, so your
673 * own application needs to be continually aware of when the next one of these
674 * moments occurs (through calling libusb_get_next_timeout()), and then it
675 * needs to call libusb_handle_events_timeout() in non-blocking mode when
676 * these moments occur. This means that you need to adjust your
677 * poll()/select() timeout accordingly.
679 * libusb provides you with a set of file descriptors to poll and expects you
680 * to poll all of them, treating them as a single entity. The meaning of each
681 * file descriptor in the set is an internal implementation detail,
682 * platform-dependent and may vary from release to release. Don't try and
683 * interpret the meaning of the file descriptors, just do as libusb indicates,
684 * polling all of them at once.
686 * In pseudo-code, you want something that looks like:
690 libusb_get_pollfds(ctx)
691 while (user has not requested application exit) {
692 libusb_get_next_timeout(ctx);
693 poll(on libusb file descriptors plus any other event sources of interest,
694 using a timeout no larger than the value libusb just suggested)
695 if (poll() indicated activity on libusb file descriptors)
696 libusb_handle_events_timeout(ctx, &zero_tv);
697 if (time has elapsed to or beyond the libusb timeout)
698 libusb_handle_events_timeout(ctx, &zero_tv);
699 // handle events from other sources here
705 * \subsection polltime Notes on time-based events
707 * The above complication with having to track time and call into libusb at
708 * specific moments is a bit of a headache. For maximum compatibility, you do
709 * need to write your main loop as above, but you may decide that you can
710 * restrict the supported platforms of your application and get away with
711 * a more simplistic scheme.
713 * These time-based event complications are \b not required on the following
716 * - Linux, provided that the following version requirements are satisfied:
717 * - Linux v2.6.27 or newer, compiled with timerfd support
718 * - glibc v2.9 or newer
719 * - libusb v1.0.5 or newer
721 * Under these configurations, libusb_get_next_timeout() will \em always return
722 * 0, so your main loop can be simplified to:
726 libusb_get_pollfds(ctx)
727 while (user has not requested application exit) {
728 poll(on libusb file descriptors plus any other event sources of interest,
729 using any timeout that you like)
730 if (poll() indicated activity on libusb file descriptors)
731 libusb_handle_events_timeout(ctx, &zero_tv);
732 // handle events from other sources here
738 * Do remember that if you simplify your main loop to the above, you will
739 * lose compatibility with some platforms (including legacy Linux platforms,
740 * and <em>any future platforms supported by libusb which may have time-based
741 * event requirements</em>). The resultant problems will likely appear as
742 * strange bugs in your application.
744 * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
745 * check to see if it is safe to ignore the time-based event complications.
746 * If your application has taken the shortcut of ignoring libusb's next timeout
747 * in your main loop, then you are advised to check the return value of
748 * libusb_pollfds_handle_timeouts() during application startup, and to abort
749 * if the platform does suffer from these timing complications.
751 * \subsection fdsetchange Changes in the file descriptor set
753 * The set of file descriptors that libusb uses as event sources may change
754 * during the life of your application. Rather than having to repeatedly
755 * call libusb_get_pollfds(), you can set up notification functions for when
756 * the file descriptor set changes using libusb_set_pollfd_notifiers().
758 * \subsection mtissues Multi-threaded considerations
760 * Unfortunately, the situation is complicated further when multiple threads
761 * come into play. If two threads are monitoring the same file descriptors,
762 * the fact that only one thread will be woken up when an event occurs causes
765 * The events lock, event waiters lock, and libusb_handle_events_locked()
766 * entities are added to solve these problems. You do not need to be concerned
767 * with these entities otherwise.
769 * See the extra documentation: \ref libusb_mtasync
772 /** \page libusb_mtasync Multi-threaded applications and asynchronous I/O
774 * libusb is a thread-safe library, but extra considerations must be applied
775 * to applications which interact with libusb from multiple threads.
777 * The underlying issue that must be addressed is that all libusb I/O
778 * revolves around monitoring file descriptors through the poll()/select()
779 * system calls. This is directly exposed at the
780 * \ref libusb_asyncio "asynchronous interface" but it is important to note that the
781 * \ref libusb_syncio "synchronous interface" is implemented on top of the
782 * asynchonrous interface, therefore the same considerations apply.
784 * The issue is that if two or more threads are concurrently calling poll()
785 * or select() on libusb's file descriptors then only one of those threads
786 * will be woken up when an event arrives. The others will be completely
787 * oblivious that anything has happened.
789 * Consider the following pseudo-code, which submits an asynchronous transfer
790 * then waits for its completion. This style is one way you could implement a
791 * synchronous interface on top of the asynchronous interface (and libusb
792 * does something similar, albeit more advanced due to the complications
793 * explained on this page).
796 void cb(struct libusb_transfer *transfer)
798 int *completed = transfer->user_data;
803 struct libusb_transfer *transfer;
804 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE] __attribute__ ((aligned (2)));
807 transfer = libusb_alloc_transfer(0);
808 libusb_fill_control_setup(buffer,
809 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
810 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
811 libusb_submit_transfer(transfer);
814 poll(libusb file descriptors, 120*1000);
815 if (poll indicates activity)
816 libusb_handle_events_timeout(ctx, &zero_tv);
818 printf("completed!");
823 * Here we are <em>serializing</em> completion of an asynchronous event
824 * against a condition - the condition being completion of a specific transfer.
825 * The poll() loop has a long timeout to minimize CPU usage during situations
826 * when nothing is happening (it could reasonably be unlimited).
828 * If this is the only thread that is polling libusb's file descriptors, there
829 * is no problem: there is no danger that another thread will swallow up the
830 * event that we are interested in. On the other hand, if there is another
831 * thread polling the same descriptors, there is a chance that it will receive
832 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
833 * will only realise that the transfer has completed on the next iteration of
834 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
835 * undesirable, and don't even think about using short timeouts to circumvent
838 * The solution here is to ensure that no two threads are ever polling the
839 * file descriptors at the same time. A naive implementation of this would
840 * impact the capabilities of the library, so libusb offers the scheme
841 * documented below to ensure no loss of functionality.
843 * Before we go any further, it is worth mentioning that all libusb-wrapped
844 * event handling procedures fully adhere to the scheme documented below.
845 * This includes libusb_handle_events() and its variants, and all the
846 * synchronous I/O functions - libusb hides this headache from you.
848 * \section Using libusb_handle_events() from multiple threads
850 * Even when only using libusb_handle_events() and synchronous I/O functions,
851 * you can still have a race condition. You might be tempted to solve the
852 * above with libusb_handle_events() like so:
855 libusb_submit_transfer(transfer);
858 libusb_handle_events(ctx);
860 printf("completed!");
863 * This however has a race between the checking of completed and
864 * libusb_handle_events() acquiring the events lock, so another thread
865 * could have completed the transfer, resulting in this thread hanging
866 * until either a timeout or another event occurs. See also commit
867 * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
868 * synchronous API implementation of libusb.
870 * Fixing this race requires checking the variable completed only after
871 * taking the event lock, which defeats the concept of just calling
872 * libusb_handle_events() without worrying about locking. This is why
873 * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
874 * and libusb_handle_events_completed() functions, which handles doing the
875 * completion check for you after they have acquired the lock:
878 libusb_submit_transfer(transfer);
881 libusb_handle_events_completed(ctx, &completed);
883 printf("completed!");
886 * This nicely fixes the race in our example. Note that if all you want to
887 * do is submit a single transfer and wait for its completion, then using
888 * one of the synchronous I/O functions is much easier.
890 * \section eventlock The events lock
892 * The problem is when we consider the fact that libusb exposes file
893 * descriptors to allow for you to integrate asynchronous USB I/O into
894 * existing main loops, effectively allowing you to do some work behind
895 * libusb's back. If you do take libusb's file descriptors and pass them to
896 * poll()/select() yourself, you need to be aware of the associated issues.
898 * The first concept to be introduced is the events lock. The events lock
899 * is used to serialize threads that want to handle events, such that only
900 * one thread is handling events at any one time.
902 * You must take the events lock before polling libusb file descriptors,
903 * using libusb_lock_events(). You must release the lock as soon as you have
904 * aborted your poll()/select() loop, using libusb_unlock_events().
906 * \section threadwait Letting other threads do the work for you
908 * Although the events lock is a critical part of the solution, it is not
909 * enough on it's own. You might wonder if the following is sufficient...
911 libusb_lock_events(ctx);
913 poll(libusb file descriptors, 120*1000);
914 if (poll indicates activity)
915 libusb_handle_events_timeout(ctx, &zero_tv);
917 libusb_unlock_events(ctx);
919 * ...and the answer is that it is not. This is because the transfer in the
920 * code shown above may take a long time (say 30 seconds) to complete, and
921 * the lock is not released until the transfer is completed.
923 * Another thread with similar code that wants to do event handling may be
924 * working with a transfer that completes after a few milliseconds. Despite
925 * having such a quick completion time, the other thread cannot check that
926 * status of its transfer until the code above has finished (30 seconds later)
927 * due to contention on the lock.
929 * To solve this, libusb offers you a mechanism to determine when another
930 * thread is handling events. It also offers a mechanism to block your thread
931 * until the event handling thread has completed an event (and this mechanism
932 * does not involve polling of file descriptors).
934 * After determining that another thread is currently handling events, you
935 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
936 * You then re-check that some other thread is still handling events, and if
937 * so, you call libusb_wait_for_event().
939 * libusb_wait_for_event() puts your application to sleep until an event
940 * occurs, or until a thread releases the events lock. When either of these
941 * things happen, your thread is woken up, and should re-check the condition
942 * it was waiting on. It should also re-check that another thread is handling
943 * events, and if not, it should start handling events itself.
945 * This looks like the following, as pseudo-code:
948 if (libusb_try_lock_events(ctx) == 0) {
949 // we obtained the event lock: do our own event handling
951 if (!libusb_event_handling_ok(ctx)) {
952 libusb_unlock_events(ctx);
955 poll(libusb file descriptors, 120*1000);
956 if (poll indicates activity)
957 libusb_handle_events_locked(ctx, 0);
959 libusb_unlock_events(ctx);
961 // another thread is doing event handling. wait for it to signal us that
962 // an event has completed
963 libusb_lock_event_waiters(ctx);
966 // now that we have the event waiters lock, double check that another
967 // thread is still handling events for us. (it may have ceased handling
968 // events in the time it took us to reach this point)
969 if (!libusb_event_handler_active(ctx)) {
970 // whoever was handling events is no longer doing so, try again
971 libusb_unlock_event_waiters(ctx);
975 libusb_wait_for_event(ctx, NULL);
977 libusb_unlock_event_waiters(ctx);
979 printf("completed!\n");
982 * A naive look at the above code may suggest that this can only support
983 * one event waiter (hence a total of 2 competing threads, the other doing
984 * event handling), because the event waiter seems to have taken the event
985 * waiters lock while waiting for an event. However, the system does support
986 * multiple event waiters, because libusb_wait_for_event() actually drops
987 * the lock while waiting, and reaquires it before continuing.
989 * We have now implemented code which can dynamically handle situations where
990 * nobody is handling events (so we should do it ourselves), and it can also
991 * handle situations where another thread is doing event handling (so we can
992 * piggyback onto them). It is also equipped to handle a combination of
993 * the two, for example, another thread is doing event handling, but for
994 * whatever reason it stops doing so before our condition is met, so we take
995 * over the event handling.
997 * Four functions were introduced in the above pseudo-code. Their importance
998 * should be apparent from the code shown above.
999 * -# libusb_try_lock_events() is a non-blocking function which attempts
1000 * to acquire the events lock but returns a failure code if it is contended.
1001 * -# libusb_event_handling_ok() checks that libusb is still happy for your
1002 * thread to be performing event handling. Sometimes, libusb needs to
1003 * interrupt the event handler, and this is how you can check if you have
1004 * been interrupted. If this function returns 0, the correct behaviour is
1005 * for you to give up the event handling lock, and then to repeat the cycle.
1006 * The following libusb_try_lock_events() will fail, so you will become an
1007 * events waiter. For more information on this, read \ref fullstory below.
1008 * -# libusb_handle_events_locked() is a variant of
1009 * libusb_handle_events_timeout() that you can call while holding the
1010 * events lock. libusb_handle_events_timeout() itself implements similar
1011 * logic to the above, so be sure not to call it when you are
1012 * "working behind libusb's back", as is the case here.
1013 * -# libusb_event_handler_active() determines if someone is currently
1014 * holding the events lock
1016 * You might be wondering why there is no function to wake up all threads
1017 * blocked on libusb_wait_for_event(). This is because libusb can do this
1018 * internally: it will wake up all such threads when someone calls
1019 * libusb_unlock_events() or when a transfer completes (at the point after its
1020 * callback has returned).
1022 * \subsection fullstory The full story
1024 * The above explanation should be enough to get you going, but if you're
1025 * really thinking through the issues then you may be left with some more
1026 * questions regarding libusb's internals. If you're curious, read on, and if
1027 * not, skip to the next section to avoid confusing yourself!
1029 * The immediate question that may spring to mind is: what if one thread
1030 * modifies the set of file descriptors that need to be polled while another
1031 * thread is doing event handling?
1033 * There are 2 situations in which this may happen.
1034 * -# libusb_open() will add another file descriptor to the poll set,
1035 * therefore it is desirable to interrupt the event handler so that it
1036 * restarts, picking up the new descriptor.
1037 * -# libusb_close() will remove a file descriptor from the poll set. There
1038 * are all kinds of race conditions that could arise here, so it is
1039 * important that nobody is doing event handling at this time.
1041 * libusb handles these issues internally, so application developers do not
1042 * have to stop their event handlers while opening/closing devices. Here's how
1043 * it works, focusing on the libusb_close() situation first:
1045 * -# During initialization, libusb opens an internal pipe, and it adds the read
1046 * end of this pipe to the set of file descriptors to be polled.
1047 * -# During libusb_close(), libusb writes some dummy data on this event pipe.
1048 * This immediately interrupts the event handler. libusb also records
1049 * internally that it is trying to interrupt event handlers for this
1050 * high-priority event.
1051 * -# At this point, some of the functions described above start behaving
1053 * - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
1054 * OK for event handling to continue.
1055 * - libusb_try_lock_events() starts returning 1, indicating that another
1056 * thread holds the event handling lock, even if the lock is uncontended.
1057 * - libusb_event_handler_active() starts returning 1, indicating that
1058 * another thread is doing event handling, even if that is not true.
1059 * -# The above changes in behaviour result in the event handler stopping and
1060 * giving up the events lock very quickly, giving the high-priority
1061 * libusb_close() operation a "free ride" to acquire the events lock. All
1062 * threads that are competing to do event handling become event waiters.
1063 * -# With the events lock held inside libusb_close(), libusb can safely remove
1064 * a file descriptor from the poll set, in the safety of knowledge that
1065 * nobody is polling those descriptors or trying to access the poll set.
1066 * -# After obtaining the events lock, the close operation completes very
1067 * quickly (usually a matter of milliseconds) and then immediately releases
1069 * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
1070 * reverts to the original, documented behaviour.
1071 * -# The release of the events lock causes the threads that are waiting for
1072 * events to be woken up and to start competing to become event handlers
1073 * again. One of them will succeed; it will then re-obtain the list of poll
1074 * descriptors, and USB I/O will then continue as normal.
1076 * libusb_open() is similar, and is actually a more simplistic case. Upon a
1077 * call to libusb_open():
1079 * -# The device is opened and a file descriptor is added to the poll set.
1080 * -# libusb sends some dummy data on the event pipe, and records that it
1081 * is trying to modify the poll descriptor set.
1082 * -# The event handler is interrupted, and the same behaviour change as for
1083 * libusb_close() takes effect, causing all event handling threads to become
1085 * -# The libusb_open() implementation takes its free ride to the events lock.
1086 * -# Happy that it has successfully paused the events handler, libusb_open()
1087 * releases the events lock.
1088 * -# The event waiter threads are all woken up and compete to become event
1089 * handlers again. The one that succeeds will obtain the list of poll
1090 * descriptors again, which will include the addition of the new device.
1092 * \subsection concl Closing remarks
1094 * The above may seem a little complicated, but hopefully I have made it clear
1095 * why such complications are necessary. Also, do not forget that this only
1096 * applies to applications that take libusb's file descriptors and integrate
1097 * them into their own polling loops.
1099 * You may decide that it is OK for your multi-threaded application to ignore
1100 * some of the rules and locks detailed above, because you don't think that
1101 * two threads can ever be polling the descriptors at the same time. If that
1102 * is the case, then that's good news for you because you don't have to worry.
1103 * But be careful here; remember that the synchronous I/O functions do event
1104 * handling internally. If you have one thread doing event handling in a loop
1105 * (without implementing the rules and locking semantics documented above)
1106 * and another trying to send a synchronous USB transfer, you will end up with
1107 * two threads monitoring the same descriptors, and the above-described
1108 * undesirable behaviour occurring. The solution is for your polling thread to
1109 * play by the rules; the synchronous I/O functions do so, and this will result
1110 * in them getting along in perfect harmony.
1112 * If you do have a dedicated thread doing event handling, it is perfectly
1113 * legal for it to take the event handling lock for long periods of time. Any
1114 * synchronous I/O functions you call from other threads will transparently
1115 * fall back to the "event waiters" mechanism detailed above. The only
1116 * consideration that your event handling thread must apply is the one related
1117 * to libusb_event_handling_ok(): you must call this before every poll(), and
1118 * give up the events lock if instructed.
1121 int usbi_io_init(struct libusb_context *ctx)
1125 usbi_mutex_init(&ctx->flying_transfers_lock);
1126 usbi_mutex_init(&ctx->events_lock);
1127 usbi_mutex_init(&ctx->event_waiters_lock);
1128 usbi_cond_init(&ctx->event_waiters_cond);
1129 usbi_mutex_init(&ctx->event_data_lock);
1130 usbi_tls_key_create(&ctx->event_handling_key);
1131 list_init(&ctx->flying_transfers);
1132 list_init(&ctx->ipollfds);
1133 list_init(&ctx->hotplug_msgs);
1134 list_init(&ctx->completed_transfers);
1136 /* FIXME should use an eventfd on kernels that support it */
1137 r = usbi_pipe(ctx->event_pipe);
1139 r = LIBUSB_ERROR_OTHER;
1143 r = usbi_add_pollfd(ctx, ctx->event_pipe[0], POLLIN);
1145 goto err_close_pipe;
1147 #ifdef USBI_TIMERFD_AVAILABLE
1148 ctx->timerfd = timerfd_create(usbi_backend.get_timerfd_clockid(),
1149 TFD_NONBLOCK | TFD_CLOEXEC);
1150 if (ctx->timerfd >= 0) {
1151 usbi_dbg("using timerfd for timeouts");
1152 r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
1154 goto err_close_timerfd;
1156 usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
1163 #ifdef USBI_TIMERFD_AVAILABLE
1165 close(ctx->timerfd);
1166 usbi_remove_pollfd(ctx, ctx->event_pipe[0]);
1169 usbi_close(ctx->event_pipe[0]);
1170 usbi_close(ctx->event_pipe[1]);
1172 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1173 usbi_mutex_destroy(&ctx->events_lock);
1174 usbi_mutex_destroy(&ctx->event_waiters_lock);
1175 usbi_cond_destroy(&ctx->event_waiters_cond);
1176 usbi_mutex_destroy(&ctx->event_data_lock);
1177 usbi_tls_key_delete(ctx->event_handling_key);
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]);
1186 #ifdef USBI_TIMERFD_AVAILABLE
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);
1201 static int calculate_timeout(struct usbi_transfer *transfer)
1204 struct timespec current_time;
1205 unsigned int timeout =
1206 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
1209 timerclear(&transfer->timeout);
1213 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, ¤t_time);
1215 usbi_err(ITRANSFER_CTX(transfer),
1216 "failed to read monotonic clock, errno=%d", errno);
1220 current_time.tv_sec += timeout / 1000;
1221 current_time.tv_nsec += (timeout % 1000) * 1000000;
1223 while (current_time.tv_nsec >= 1000000000) {
1224 current_time.tv_nsec -= 1000000000;
1225 current_time.tv_sec++;
1228 TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
1232 /** \ingroup libusb_asyncio
1233 * Allocate a libusb transfer with a specified number of isochronous packet
1234 * descriptors. The returned transfer is pre-initialized for you. When the new
1235 * transfer is no longer needed, it should be freed with
1236 * libusb_free_transfer().
1238 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
1239 * interrupt) should specify an iso_packets count of zero.
1241 * For transfers intended for isochronous endpoints, specify an appropriate
1242 * number of packet descriptors to be allocated as part of the transfer.
1243 * The returned transfer is not specially initialized for isochronous I/O;
1244 * you are still required to set the
1245 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
1246 * \ref libusb_transfer::type "type" fields accordingly.
1248 * It is safe to allocate a transfer with some isochronous packets and then
1249 * use it on a non-isochronous endpoint. If you do this, ensure that at time
1250 * of submission, num_iso_packets is 0 and that type is set appropriately.
1252 * \param iso_packets number of isochronous packet descriptors to allocate. Must be non-negative.
1253 * \returns a newly allocated transfer, or NULL on error
1256 struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
1259 struct libusb_transfer *transfer;
1260 size_t os_alloc_size;
1262 struct usbi_transfer *itransfer;
1264 assert(iso_packets >= 0);
1266 os_alloc_size = usbi_backend.transfer_priv_size;
1267 alloc_size = sizeof(struct usbi_transfer)
1268 + sizeof(struct libusb_transfer)
1269 + (sizeof(struct libusb_iso_packet_descriptor) * (size_t)iso_packets)
1271 itransfer = calloc(1, alloc_size);
1275 itransfer->num_iso_packets = iso_packets;
1276 usbi_mutex_init(&itransfer->lock);
1277 transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1278 usbi_dbg("transfer %p", transfer);
1282 /** \ingroup libusb_asyncio
1283 * Free a transfer structure. This should be called for all transfers
1284 * allocated with libusb_alloc_transfer().
1286 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
1287 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
1288 * non-NULL, this function will also free the transfer buffer using the
1289 * standard system memory allocator (e.g. free()).
1291 * It is legal to call this function with a NULL transfer. In this case,
1292 * the function will simply return safely.
1294 * It is not legal to free an active transfer (one which has been submitted
1295 * and has not yet completed).
1297 * \param transfer the transfer to free
1299 void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
1301 struct usbi_transfer *itransfer;
1305 usbi_dbg("transfer %p", transfer);
1306 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER)
1307 free(transfer->buffer);
1309 itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1310 usbi_mutex_destroy(&itransfer->lock);
1314 #ifdef USBI_TIMERFD_AVAILABLE
1315 static int disarm_timerfd(struct libusb_context *ctx)
1317 const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
1321 r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
1323 return LIBUSB_ERROR_OTHER;
1328 /* iterates through the flying transfers, and rearms the timerfd based on the
1329 * next upcoming timeout.
1330 * must be called with flying_list locked.
1331 * returns 0 on success or a LIBUSB_ERROR code on failure.
1333 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1335 struct usbi_transfer *transfer;
1337 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1338 struct timeval *cur_tv = &transfer->timeout;
1340 /* if we've reached transfers of infinite timeout, then we have no
1342 if (!timerisset(cur_tv))
1345 /* act on first transfer that has not already been handled */
1346 if (!(transfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))) {
1348 const struct itimerspec it = { {0, 0},
1349 { cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
1350 usbi_dbg("next timeout originally %dms", USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1351 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1353 return LIBUSB_ERROR_OTHER;
1359 return disarm_timerfd(ctx);
1362 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1369 /* add a transfer to the (timeout-sorted) active transfers list.
1370 * This function will return non 0 if fails to update the timer,
1371 * in which case the transfer is *not* on the flying_transfers list. */
1372 static int add_to_flying_list(struct usbi_transfer *transfer)
1374 struct usbi_transfer *cur;
1375 struct timeval *timeout = &transfer->timeout;
1376 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1380 r = calculate_timeout(transfer);
1384 /* if we have no other flying transfers, start the list with this one */
1385 if (list_empty(&ctx->flying_transfers)) {
1386 list_add(&transfer->list, &ctx->flying_transfers);
1390 /* if we have infinite timeout, append to end of list */
1391 if (!timerisset(timeout)) {
1392 list_add_tail(&transfer->list, &ctx->flying_transfers);
1393 /* first is irrelevant in this case */
1397 /* otherwise, find appropriate place in list */
1398 list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
1399 /* find first timeout that occurs after the transfer in question */
1400 struct timeval *cur_tv = &cur->timeout;
1402 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
1403 (cur_tv->tv_sec == timeout->tv_sec &&
1404 cur_tv->tv_usec > timeout->tv_usec)) {
1405 list_add_tail(&transfer->list, &cur->list);
1410 /* first is 0 at this stage (list not empty) */
1412 /* otherwise we need to be inserted at the end */
1413 list_add_tail(&transfer->list, &ctx->flying_transfers);
1415 #ifdef USBI_TIMERFD_AVAILABLE
1416 if (first && usbi_using_timerfd(ctx) && timerisset(timeout)) {
1417 /* if this transfer has the lowest timeout of all active transfers,
1418 * rearm the timerfd with this transfer's timeout */
1419 const struct itimerspec it = { {0, 0},
1420 { timeout->tv_sec, timeout->tv_usec * 1000 } };
1421 usbi_dbg("arm timerfd for timeout in %dms (first in line)",
1422 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1423 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1425 usbi_warn(ctx, "failed to arm first timerfd (errno %d)", errno);
1426 r = LIBUSB_ERROR_OTHER;
1434 list_del(&transfer->list);
1439 /* remove a transfer from the active transfers list.
1440 * This function will *always* remove the transfer from the
1441 * flying_transfers list. It will return a LIBUSB_ERROR code
1442 * if it fails to update the timer for the next timeout. */
1443 static int remove_from_flying_list(struct usbi_transfer *transfer)
1445 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1449 usbi_mutex_lock(&ctx->flying_transfers_lock);
1450 rearm_timerfd = (timerisset(&transfer->timeout) &&
1451 list_first_entry(&ctx->flying_transfers, struct usbi_transfer, list) == transfer);
1452 list_del(&transfer->list);
1453 if (usbi_using_timerfd(ctx) && rearm_timerfd)
1454 r = arm_timerfd_for_next_timeout(ctx);
1455 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1460 /** \ingroup libusb_asyncio
1461 * Submit a transfer. This function will fire off the USB transfer and then
1462 * return immediately.
1464 * \param transfer the transfer to submit
1465 * \returns 0 on success
1466 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
1467 * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
1468 * \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
1469 * by the operating system.
1470 * \returns LIBUSB_ERROR_INVALID_PARAM if the transfer size is larger than
1471 * the operating system and/or hardware can support
1472 * \returns another LIBUSB_ERROR code on other failure
1474 int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
1476 struct usbi_transfer *itransfer =
1477 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1478 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1481 usbi_dbg("transfer %p", transfer);
1484 * Important note on locking, this function takes / releases locks
1485 * in the following order:
1486 * take flying_transfers_lock
1487 * take itransfer->lock
1489 * add to flying_transfers list
1490 * release flying_transfers_lock
1492 * release itransfer->lock
1494 * take flying_transfers_lock
1495 * remove from flying_transfers list
1496 * release flying_transfers_lock
1498 * Note that it takes locks in the order a-b and then releases them
1499 * in the same order a-b. This is somewhat unusual but not wrong,
1500 * release order is not important as long as *all* locks are released
1501 * before re-acquiring any locks.
1503 * This means that the ordering of first releasing itransfer->lock
1504 * and then re-acquiring the flying_transfers_list on error is
1505 * important and must not be changed!
1507 * This is done this way because when we take both locks we must always
1508 * take flying_transfers_lock first to avoid ab-ba style deadlocks with
1509 * the timeout handling and usbi_handle_disconnect paths.
1511 * And we cannot release itransfer->lock before the submission is
1512 * complete otherwise timeout handling for transfers with short
1513 * timeouts may run before submission.
1515 usbi_mutex_lock(&ctx->flying_transfers_lock);
1516 usbi_mutex_lock(&itransfer->lock);
1517 if (itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT) {
1518 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1519 usbi_mutex_unlock(&itransfer->lock);
1520 return LIBUSB_ERROR_BUSY;
1522 itransfer->transferred = 0;
1523 itransfer->state_flags = 0;
1524 itransfer->timeout_flags = 0;
1525 r = add_to_flying_list(itransfer);
1527 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1528 usbi_mutex_unlock(&itransfer->lock);
1532 * We must release the flying transfers lock here, because with
1533 * some backends the submit_transfer method is synchroneous.
1535 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1537 r = usbi_backend.submit_transfer(itransfer);
1538 if (r == LIBUSB_SUCCESS) {
1539 itransfer->state_flags |= USBI_TRANSFER_IN_FLIGHT;
1540 /* keep a reference to this device */
1541 libusb_ref_device(transfer->dev_handle->dev);
1543 usbi_mutex_unlock(&itransfer->lock);
1545 if (r != LIBUSB_SUCCESS)
1546 remove_from_flying_list(itransfer);
1551 /** \ingroup libusb_asyncio
1552 * Asynchronously cancel a previously submitted transfer.
1553 * This function returns immediately, but this does not indicate cancellation
1554 * is complete. Your callback function will be invoked at some later time
1555 * with a transfer status of
1556 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
1557 * "LIBUSB_TRANSFER_CANCELLED."
1559 * \param transfer the transfer to cancel
1560 * \returns 0 on success
1561 * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is not in progress,
1562 * already complete, or already cancelled.
1563 * \returns a LIBUSB_ERROR code on failure
1565 int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
1567 struct usbi_transfer *itransfer =
1568 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1571 usbi_dbg("transfer %p", transfer );
1572 usbi_mutex_lock(&itransfer->lock);
1573 if (!(itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT)
1574 || (itransfer->state_flags & USBI_TRANSFER_CANCELLING)) {
1575 r = LIBUSB_ERROR_NOT_FOUND;
1578 r = usbi_backend.cancel_transfer(itransfer);
1580 if (r != LIBUSB_ERROR_NOT_FOUND &&
1581 r != LIBUSB_ERROR_NO_DEVICE)
1582 usbi_err(TRANSFER_CTX(transfer),
1583 "cancel transfer failed error %d", r);
1585 usbi_dbg("cancel transfer failed error %d", r);
1587 if (r == LIBUSB_ERROR_NO_DEVICE)
1588 itransfer->state_flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
1591 itransfer->state_flags |= USBI_TRANSFER_CANCELLING;
1594 usbi_mutex_unlock(&itransfer->lock);
1598 /** \ingroup libusb_asyncio
1599 * Set a transfers bulk stream id. Note users are advised to use
1600 * libusb_fill_bulk_stream_transfer() instead of calling this function
1603 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1605 * \param transfer the transfer to set the stream id for
1606 * \param stream_id the stream id to set
1607 * \see libusb_alloc_streams()
1609 void API_EXPORTED libusb_transfer_set_stream_id(
1610 struct libusb_transfer *transfer, uint32_t stream_id)
1612 struct usbi_transfer *itransfer =
1613 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1615 itransfer->stream_id = stream_id;
1618 /** \ingroup libusb_asyncio
1619 * Get a transfers bulk stream id.
1621 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1623 * \param transfer the transfer to get the stream id for
1624 * \returns the stream id for the transfer
1626 uint32_t API_EXPORTED libusb_transfer_get_stream_id(
1627 struct libusb_transfer *transfer)
1629 struct usbi_transfer *itransfer =
1630 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1632 return itransfer->stream_id;
1635 /* Handle completion of a transfer (completion might be an error condition).
1636 * This will invoke the user-supplied callback function, which may end up
1637 * freeing the transfer. Therefore you cannot use the transfer structure
1638 * after calling this function, and you should free all backend-specific
1639 * data before calling it.
1640 * Do not call this function with the usbi_transfer lock held. User-specified
1641 * callback functions may attempt to directly resubmit the transfer, which
1642 * will attempt to take the lock. */
1643 int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1644 enum libusb_transfer_status status)
1646 struct libusb_transfer *transfer =
1647 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1648 struct libusb_device_handle *dev_handle = transfer->dev_handle;
1652 r = remove_from_flying_list(itransfer);
1654 usbi_err(ITRANSFER_CTX(itransfer), "failed to set timer for next timeout, errno=%d", errno);
1656 usbi_mutex_lock(&itransfer->lock);
1657 itransfer->state_flags &= ~USBI_TRANSFER_IN_FLIGHT;
1658 usbi_mutex_unlock(&itransfer->lock);
1660 if (status == LIBUSB_TRANSFER_COMPLETED
1661 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1662 int rqlen = transfer->length;
1663 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1664 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1665 if (rqlen != itransfer->transferred) {
1666 usbi_dbg("interpreting short transfer as error");
1667 status = LIBUSB_TRANSFER_ERROR;
1671 flags = transfer->flags;
1672 transfer->status = status;
1673 transfer->actual_length = itransfer->transferred;
1674 usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
1675 if (transfer->callback)
1676 transfer->callback(transfer);
1677 /* transfer might have been freed by the above call, do not use from
1679 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1680 libusb_free_transfer(transfer);
1681 libusb_unref_device(dev_handle->dev);
1685 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1686 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1687 * transfers exist here.
1688 * Do not call this function with the usbi_transfer lock held. User-specified
1689 * callback functions may attempt to directly resubmit the transfer, which
1690 * will attempt to take the lock. */
1691 int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
1693 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1696 usbi_mutex_lock(&ctx->flying_transfers_lock);
1697 timed_out = transfer->timeout_flags & USBI_TRANSFER_TIMED_OUT;
1698 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1700 /* if the URB was cancelled due to timeout, report timeout to the user */
1702 usbi_dbg("detected timeout cancellation");
1703 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
1706 /* otherwise its a normal async cancel */
1707 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
1710 /* Add a completed transfer to the completed_transfers list of the
1711 * context and signal the event. The backend's handle_transfer_completion()
1712 * function will be called the next time an event handler runs. */
1713 void usbi_signal_transfer_completion(struct usbi_transfer *transfer)
1715 libusb_device_handle *dev_handle = USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->dev_handle;
1718 struct libusb_context *ctx = HANDLE_CTX(dev_handle);
1721 usbi_mutex_lock(&ctx->event_data_lock);
1722 pending_events = usbi_pending_events(ctx);
1723 list_add_tail(&transfer->completed_list, &ctx->completed_transfers);
1724 if (!pending_events)
1725 usbi_signal_event(ctx);
1726 usbi_mutex_unlock(&ctx->event_data_lock);
1730 /** \ingroup libusb_poll
1731 * Attempt to acquire the event handling lock. This lock is used to ensure that
1732 * only one thread is monitoring libusb event sources at any one time.
1734 * You only need to use this lock if you are developing an application
1735 * which calls poll() or select() on libusb's file descriptors directly.
1736 * If you stick to libusb's event handling loop functions (e.g.
1737 * libusb_handle_events()) then you do not need to be concerned with this
1740 * While holding this lock, you are trusted to actually be handling events.
1741 * If you are no longer handling events, you must call libusb_unlock_events()
1742 * as soon as possible.
1744 * \param ctx the context to operate on, or NULL for the default context
1745 * \returns 0 if the lock was obtained successfully
1746 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1747 * \ref libusb_mtasync
1749 int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
1753 USBI_GET_CONTEXT(ctx);
1755 /* is someone else waiting to close a device? if so, don't let this thread
1756 * start event handling */
1757 usbi_mutex_lock(&ctx->event_data_lock);
1758 ru = ctx->device_close;
1759 usbi_mutex_unlock(&ctx->event_data_lock);
1761 usbi_dbg("someone else is closing a device");
1765 r = usbi_mutex_trylock(&ctx->events_lock);
1769 ctx->event_handler_active = 1;
1773 /** \ingroup libusb_poll
1774 * Acquire the event handling lock, blocking until successful acquisition if
1775 * it is contended. This lock is used to ensure that only one thread is
1776 * monitoring libusb event sources at any one time.
1778 * You only need to use this lock if you are developing an application
1779 * which calls poll() or select() on libusb's file descriptors directly.
1780 * If you stick to libusb's event handling loop functions (e.g.
1781 * libusb_handle_events()) then you do not need to be concerned with this
1784 * While holding this lock, you are trusted to actually be handling events.
1785 * If you are no longer handling events, you must call libusb_unlock_events()
1786 * as soon as possible.
1788 * \param ctx the context to operate on, or NULL for the default context
1789 * \ref libusb_mtasync
1791 void API_EXPORTED libusb_lock_events(libusb_context *ctx)
1793 USBI_GET_CONTEXT(ctx);
1794 usbi_mutex_lock(&ctx->events_lock);
1795 ctx->event_handler_active = 1;
1798 /** \ingroup libusb_poll
1799 * Release the lock previously acquired with libusb_try_lock_events() or
1800 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1801 * on libusb_wait_for_event().
1803 * \param ctx the context to operate on, or NULL for the default context
1804 * \ref libusb_mtasync
1806 void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
1808 USBI_GET_CONTEXT(ctx);
1809 ctx->event_handler_active = 0;
1810 usbi_mutex_unlock(&ctx->events_lock);
1812 /* FIXME: perhaps we should be a bit more efficient by not broadcasting
1813 * the availability of the events lock when we are modifying pollfds
1814 * (check ctx->device_close)? */
1815 usbi_mutex_lock(&ctx->event_waiters_lock);
1816 usbi_cond_broadcast(&ctx->event_waiters_cond);
1817 usbi_mutex_unlock(&ctx->event_waiters_lock);
1820 /** \ingroup libusb_poll
1821 * Determine if it is still OK for this thread to be doing event handling.
1823 * Sometimes, libusb needs to temporarily pause all event handlers, and this
1824 * is the function you should use before polling file descriptors to see if
1827 * If this function instructs your thread to give up the events lock, you
1828 * should just continue the usual logic that is documented in \ref libusb_mtasync.
1829 * On the next iteration, your thread will fail to obtain the events lock,
1830 * and will hence become an event waiter.
1832 * This function should be called while the events lock is held: you don't
1833 * need to worry about the results of this function if your thread is not
1834 * the current event handler.
1836 * \param ctx the context to operate on, or NULL for the default context
1837 * \returns 1 if event handling can start or continue
1838 * \returns 0 if this thread must give up the events lock
1839 * \ref fullstory "Multi-threaded I/O: the full story"
1841 int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
1844 USBI_GET_CONTEXT(ctx);
1846 /* is someone else waiting to close a device? if so, don't let this thread
1847 * continue event handling */
1848 usbi_mutex_lock(&ctx->event_data_lock);
1849 r = ctx->device_close;
1850 usbi_mutex_unlock(&ctx->event_data_lock);
1852 usbi_dbg("someone else is closing a device");
1860 /** \ingroup libusb_poll
1861 * Determine if an active thread is handling events (i.e. if anyone is holding
1862 * the event handling lock).
1864 * \param ctx the context to operate on, or NULL for the default context
1865 * \returns 1 if a thread is handling events
1866 * \returns 0 if there are no threads currently handling events
1867 * \ref libusb_mtasync
1869 int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
1872 USBI_GET_CONTEXT(ctx);
1874 /* is someone else waiting to close a device? if so, don't let this thread
1875 * start event handling -- indicate that event handling is happening */
1876 usbi_mutex_lock(&ctx->event_data_lock);
1877 r = ctx->device_close;
1878 usbi_mutex_unlock(&ctx->event_data_lock);
1880 usbi_dbg("someone else is closing a device");
1884 return ctx->event_handler_active;
1887 /** \ingroup libusb_poll
1888 * Interrupt any active thread that is handling events. This is mainly useful
1889 * for interrupting a dedicated event handling thread when an application
1890 * wishes to call libusb_exit().
1892 * Since version 1.0.21, \ref LIBUSB_API_VERSION >= 0x01000105
1894 * \param ctx the context to operate on, or NULL for the default context
1895 * \ref libusb_mtasync
1897 void API_EXPORTED libusb_interrupt_event_handler(libusb_context *ctx)
1900 USBI_GET_CONTEXT(ctx);
1903 usbi_mutex_lock(&ctx->event_data_lock);
1905 pending_events = usbi_pending_events(ctx);
1906 ctx->event_flags |= USBI_EVENT_USER_INTERRUPT;
1907 if (!pending_events)
1908 usbi_signal_event(ctx);
1910 usbi_mutex_unlock(&ctx->event_data_lock);
1913 /** \ingroup libusb_poll
1914 * Acquire the event waiters lock. This lock is designed to be obtained under
1915 * the situation where you want to be aware when events are completed, but
1916 * some other thread is event handling so calling libusb_handle_events() is not
1919 * You then obtain this lock, re-check that another thread is still handling
1920 * events, then call libusb_wait_for_event().
1922 * You only need to use this lock if you are developing an application
1923 * which calls poll() or select() on libusb's file descriptors directly,
1924 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1925 * If you stick to libusb's event handling loop functions (e.g.
1926 * libusb_handle_events()) then you do not need to be concerned with this
1929 * \param ctx the context to operate on, or NULL for the default context
1930 * \ref libusb_mtasync
1932 void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
1934 USBI_GET_CONTEXT(ctx);
1935 usbi_mutex_lock(&ctx->event_waiters_lock);
1938 /** \ingroup libusb_poll
1939 * Release the event waiters lock.
1940 * \param ctx the context to operate on, or NULL for the default context
1941 * \ref libusb_mtasync
1943 void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
1945 USBI_GET_CONTEXT(ctx);
1946 usbi_mutex_unlock(&ctx->event_waiters_lock);
1949 /** \ingroup libusb_poll
1950 * Wait for another thread to signal completion of an event. Must be called
1951 * with the event waiters lock held, see libusb_lock_event_waiters().
1953 * This function will block until any of the following conditions are met:
1954 * -# The timeout expires
1955 * -# A transfer completes
1956 * -# A thread releases the event handling lock through libusb_unlock_events()
1958 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1959 * the callback for the transfer has completed. Condition 3 is important
1960 * because it means that the thread that was previously handling events is no
1961 * longer doing so, so if any events are to complete, another thread needs to
1962 * step up and start event handling.
1964 * This function releases the event waiters lock before putting your thread
1965 * to sleep, and reacquires the lock as it is being woken up.
1967 * \param ctx the context to operate on, or NULL for the default context
1968 * \param tv maximum timeout for this blocking function. A NULL value
1969 * indicates unlimited timeout.
1970 * \returns 0 after a transfer completes or another thread stops event handling
1971 * \returns 1 if the timeout expired
1972 * \ref libusb_mtasync
1974 int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
1978 USBI_GET_CONTEXT(ctx);
1980 usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
1984 r = usbi_cond_timedwait(&ctx->event_waiters_cond,
1985 &ctx->event_waiters_lock, tv);
1990 return (r == ETIMEDOUT);
1993 static void handle_timeout(struct usbi_transfer *itransfer)
1995 struct libusb_transfer *transfer =
1996 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1999 itransfer->timeout_flags |= USBI_TRANSFER_TIMEOUT_HANDLED;
2000 r = libusb_cancel_transfer(transfer);
2001 if (r == LIBUSB_SUCCESS)
2002 itransfer->timeout_flags |= USBI_TRANSFER_TIMED_OUT;
2004 usbi_warn(TRANSFER_CTX(transfer),
2005 "async cancel failed %d errno=%d", r, errno);
2008 static int handle_timeouts_locked(struct libusb_context *ctx)
2011 struct timespec systime_ts;
2012 struct timeval systime;
2013 struct usbi_transfer *transfer;
2015 if (list_empty(&ctx->flying_transfers))
2018 /* get current time */
2019 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
2023 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
2025 /* iterate through flying transfers list, finding all transfers that
2026 * have expired timeouts */
2027 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2028 struct timeval *cur_tv = &transfer->timeout;
2030 /* if we've reached transfers of infinite timeout, we're all done */
2031 if (!timerisset(cur_tv))
2034 /* ignore timeouts we've already handled */
2035 if (transfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2038 /* if transfer has non-expired timeout, nothing more to do */
2039 if ((cur_tv->tv_sec > systime.tv_sec) ||
2040 (cur_tv->tv_sec == systime.tv_sec &&
2041 cur_tv->tv_usec > systime.tv_usec))
2044 /* otherwise, we've got an expired timeout to handle */
2045 handle_timeout(transfer);
2050 static int handle_timeouts(struct libusb_context *ctx)
2053 USBI_GET_CONTEXT(ctx);
2054 usbi_mutex_lock(&ctx->flying_transfers_lock);
2055 r = handle_timeouts_locked(ctx);
2056 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2060 #ifdef USBI_TIMERFD_AVAILABLE
2061 static int handle_timerfd_trigger(struct libusb_context *ctx)
2065 usbi_mutex_lock(&ctx->flying_transfers_lock);
2067 /* process the timeout that just happened */
2068 r = handle_timeouts_locked(ctx);
2072 /* arm for next timeout*/
2073 r = arm_timerfd_for_next_timeout(ctx);
2076 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2081 /* do the actual event handling. assumes that no other thread is concurrently
2082 * doing the same thing. */
2083 static int handle_events(struct libusb_context *ctx, struct timeval *tv)
2086 struct usbi_pollfd *ipollfd;
2087 POLL_NFDS_TYPE nfds = 0;
2088 POLL_NFDS_TYPE internal_nfds;
2089 struct pollfd *fds = NULL;
2093 /* prevent attempts to recursively handle events (e.g. calling into
2094 * libusb_handle_events() from within a hotplug or transfer callback) */
2095 usbi_mutex_lock(&ctx->event_data_lock);
2097 if (usbi_handling_events(ctx))
2098 r = LIBUSB_ERROR_BUSY;
2100 usbi_start_event_handling(ctx);
2101 usbi_mutex_unlock(&ctx->event_data_lock);
2106 /* there are certain fds that libusb uses internally, currently:
2111 * the backend will never need to attempt to handle events on these fds, so
2112 * we determine how many fds are in use internally for this context and when
2113 * handle_events() is called in the backend, the pollfd list and count will
2114 * be adjusted to skip over these internal fds */
2115 if (usbi_using_timerfd(ctx))
2120 /* only reallocate the poll fds when the list of poll fds has been modified
2121 * since the last poll, otherwise reuse them to save the additional overhead */
2122 usbi_mutex_lock(&ctx->event_data_lock);
2123 if (ctx->event_flags & USBI_EVENT_POLLFDS_MODIFIED) {
2124 usbi_dbg("poll fds modified, reallocating");
2127 ctx->pollfds = NULL;
2129 /* sanity check - it is invalid for a context to have fewer than the
2130 * required internal fds (memory corruption?) */
2131 assert(ctx->pollfds_cnt >= internal_nfds);
2133 ctx->pollfds = calloc(ctx->pollfds_cnt, sizeof(*ctx->pollfds));
2134 if (!ctx->pollfds) {
2135 usbi_mutex_unlock(&ctx->event_data_lock);
2136 r = LIBUSB_ERROR_NO_MEM;
2140 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd) {
2141 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
2143 ctx->pollfds[i].fd = pollfd->fd;
2144 ctx->pollfds[i].events = pollfd->events;
2147 /* reset the flag now that we have the updated list */
2148 ctx->event_flags &= ~USBI_EVENT_POLLFDS_MODIFIED;
2150 /* if no further pending events, clear the event pipe so that we do
2151 * not immediately return from poll */
2152 if (!usbi_pending_events(ctx))
2153 usbi_clear_event(ctx);
2156 nfds = ctx->pollfds_cnt;
2157 usbi_inc_fds_ref(fds, nfds);
2158 usbi_mutex_unlock(&ctx->event_data_lock);
2160 timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000);
2162 /* round up to next millisecond */
2163 if (tv->tv_usec % 1000)
2166 usbi_dbg("poll() %d fds with timeout in %dms", (int)nfds, timeout_ms);
2167 r = usbi_poll(fds, nfds, timeout_ms);
2168 usbi_dbg("poll() returned %d", r);
2170 r = handle_timeouts(ctx);
2172 } else if (r == -1 && errno == EINTR) {
2173 r = LIBUSB_ERROR_INTERRUPTED;
2176 usbi_err(ctx, "poll failed %d err=%d", r, errno);
2177 r = LIBUSB_ERROR_IO;
2181 /* fds[0] is always the event pipe */
2182 if (fds[0].revents) {
2183 struct list_head hotplug_msgs;
2184 struct usbi_transfer *itransfer;
2185 int hotplug_cb_deregistered = 0;
2188 list_init(&hotplug_msgs);
2190 usbi_dbg("caught a fish on the event pipe");
2192 /* take the the event data lock while processing events */
2193 usbi_mutex_lock(&ctx->event_data_lock);
2195 /* check if someone added a new poll fd */
2196 if (ctx->event_flags & USBI_EVENT_POLLFDS_MODIFIED)
2197 usbi_dbg("someone updated the poll fds");
2199 if (ctx->event_flags & USBI_EVENT_USER_INTERRUPT) {
2200 usbi_dbg("someone purposely interrupted");
2201 ctx->event_flags &= ~USBI_EVENT_USER_INTERRUPT;
2204 if (ctx->event_flags & USBI_EVENT_HOTPLUG_CB_DEREGISTERED) {
2205 usbi_dbg("someone unregistered a hotplug cb");
2206 ctx->event_flags &= ~USBI_EVENT_HOTPLUG_CB_DEREGISTERED;
2207 hotplug_cb_deregistered = 1;
2210 /* check if someone is closing a device */
2211 if (ctx->device_close)
2212 usbi_dbg("someone is closing a device");
2214 /* check for any pending hotplug messages */
2215 if (!list_empty(&ctx->hotplug_msgs)) {
2216 usbi_dbg("hotplug message received");
2217 list_cut(&hotplug_msgs, &ctx->hotplug_msgs);
2220 /* complete any pending transfers */
2221 while (ret == 0 && !list_empty(&ctx->completed_transfers)) {
2222 itransfer = list_first_entry(&ctx->completed_transfers, struct usbi_transfer, completed_list);
2223 list_del(&itransfer->completed_list);
2224 usbi_mutex_unlock(&ctx->event_data_lock);
2225 ret = usbi_backend.handle_transfer_completion(itransfer);
2227 usbi_err(ctx, "backend handle_transfer_completion failed with error %d", ret);
2228 usbi_mutex_lock(&ctx->event_data_lock);
2231 /* if no further pending events, clear the event pipe */
2232 if (!usbi_pending_events(ctx))
2233 usbi_clear_event(ctx);
2235 usbi_mutex_unlock(&ctx->event_data_lock);
2237 if (hotplug_cb_deregistered)
2238 usbi_hotplug_deregister(ctx, 0);
2240 /* process the hotplug messages, if any */
2241 while (!list_empty(&hotplug_msgs)) {
2242 struct libusb_hotplug_message *message =
2243 list_first_entry(&hotplug_msgs, struct libusb_hotplug_message, list);
2245 usbi_hotplug_match(ctx, message->device, message->event);
2247 /* the device left, dereference the device */
2248 if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == message->event)
2249 libusb_unref_device(message->device);
2251 list_del(&message->list);
2256 /* return error code */
2265 #ifdef USBI_TIMERFD_AVAILABLE
2266 /* on timerfd configurations, fds[1] is the timerfd */
2267 if (usbi_using_timerfd(ctx) && fds[1].revents) {
2268 /* timerfd indicates that a timeout has expired */
2270 usbi_dbg("timerfd triggered");
2272 ret = handle_timerfd_trigger(ctx);
2274 /* return error code */
2284 r = usbi_backend.handle_events(ctx, fds + internal_nfds, nfds - internal_nfds, r);
2286 usbi_err(ctx, "backend handle_events failed with error %d", r);
2289 usbi_end_event_handling(ctx);
2290 usbi_dec_fds_ref(fds, nfds);
2294 /* returns the smallest of:
2295 * 1. timeout of next URB
2296 * 2. user-supplied timeout
2297 * returns 1 if there is an already-expired timeout, otherwise returns 0
2300 static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
2301 struct timeval *out)
2303 struct timeval timeout;
2304 int r = libusb_get_next_timeout(ctx, &timeout);
2306 /* timeout already expired? */
2307 if (!timerisset(&timeout))
2310 /* choose the smallest of next URB timeout or user specified timeout */
2311 if (timercmp(&timeout, tv, <))
2321 /** \ingroup libusb_poll
2322 * Handle any pending events.
2324 * libusb determines "pending events" by checking if any timeouts have expired
2325 * and by checking the set of file descriptors for activity.
2327 * If a zero timeval is passed, this function will handle any already-pending
2328 * events and then immediately return in non-blocking style.
2330 * If a non-zero timeval is passed and no events are currently pending, this
2331 * function will block waiting for events to handle up until the specified
2332 * timeout. If an event arrives or a signal is raised, this function will
2335 * If the parameter completed is not NULL then <em>after obtaining the event
2336 * handling lock</em> this function will return immediately if the integer
2337 * pointed to is not 0. This allows for race free waiting for the completion
2338 * of a specific transfer.
2340 * \param ctx the context to operate on, or NULL for the default context
2341 * \param tv the maximum time to block waiting for events, or an all zero
2342 * timeval struct for non-blocking mode
2343 * \param completed pointer to completion integer to check, or NULL
2344 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2345 * \ref libusb_mtasync
2347 int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
2348 struct timeval *tv, int *completed)
2351 struct timeval poll_timeout;
2353 USBI_GET_CONTEXT(ctx);
2354 r = get_next_timeout(ctx, tv, &poll_timeout);
2356 /* timeout already expired */
2357 return handle_timeouts(ctx);
2361 if (libusb_try_lock_events(ctx) == 0) {
2362 if (completed == NULL || !*completed) {
2363 /* we obtained the event lock: do our own event handling */
2364 usbi_dbg("doing our own event handling");
2365 r = handle_events(ctx, &poll_timeout);
2367 libusb_unlock_events(ctx);
2371 /* another thread is doing event handling. wait for thread events that
2372 * notify event completion. */
2373 libusb_lock_event_waiters(ctx);
2375 if (completed && *completed)
2378 if (!libusb_event_handler_active(ctx)) {
2379 /* we hit a race: whoever was event handling earlier finished in the
2380 * time it took us to reach this point. try the cycle again. */
2381 libusb_unlock_event_waiters(ctx);
2382 usbi_dbg("event handler was active but went away, retrying");
2386 usbi_dbg("another thread is doing event handling");
2387 r = libusb_wait_for_event(ctx, &poll_timeout);
2390 libusb_unlock_event_waiters(ctx);
2395 return handle_timeouts(ctx);
2400 /** \ingroup libusb_poll
2401 * Handle any pending events
2403 * Like libusb_handle_events_timeout_completed(), but without the completed
2404 * parameter, calling this function is equivalent to calling
2405 * libusb_handle_events_timeout_completed() with a NULL completed parameter.
2407 * This function is kept primarily for backwards compatibility.
2408 * All new code should call libusb_handle_events_completed() or
2409 * libusb_handle_events_timeout_completed() to avoid race conditions.
2411 * \param ctx the context to operate on, or NULL for the default context
2412 * \param tv the maximum time to block waiting for events, or an all zero
2413 * timeval struct for non-blocking mode
2414 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2416 int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
2419 return libusb_handle_events_timeout_completed(ctx, tv, NULL);
2422 /** \ingroup libusb_poll
2423 * Handle any pending events in blocking mode. There is currently a timeout
2424 * hardcoded at 60 seconds but we plan to make it unlimited in future. For
2425 * finer control over whether this function is blocking or non-blocking, or
2426 * for control over the timeout, use libusb_handle_events_timeout_completed()
2429 * This function is kept primarily for backwards compatibility.
2430 * All new code should call libusb_handle_events_completed() or
2431 * libusb_handle_events_timeout_completed() to avoid race conditions.
2433 * \param ctx the context to operate on, or NULL for the default context
2434 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2436 int API_EXPORTED libusb_handle_events(libusb_context *ctx)
2441 return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
2444 /** \ingroup libusb_poll
2445 * Handle any pending events in blocking mode.
2447 * Like libusb_handle_events(), with the addition of a completed parameter
2448 * to allow for race free waiting for the completion of a specific transfer.
2450 * See libusb_handle_events_timeout_completed() for details on the completed
2453 * \param ctx the context to operate on, or NULL for the default context
2454 * \param completed pointer to completion integer to check, or NULL
2455 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2456 * \ref libusb_mtasync
2458 int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
2464 return libusb_handle_events_timeout_completed(ctx, &tv, completed);
2467 /** \ingroup libusb_poll
2468 * Handle any pending events by polling file descriptors, without checking if
2469 * any other threads are already doing so. Must be called with the event lock
2470 * held, see libusb_lock_events().
2472 * This function is designed to be called under the situation where you have
2473 * taken the event lock and are calling poll()/select() directly on libusb's
2474 * file descriptors (as opposed to using libusb_handle_events() or similar).
2475 * You detect events on libusb's descriptors, so you then call this function
2476 * with a zero timeout value (while still holding the event lock).
2478 * \param ctx the context to operate on, or NULL for the default context
2479 * \param tv the maximum time to block waiting for events, or zero for
2481 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2482 * \ref libusb_mtasync
2484 int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
2488 struct timeval poll_timeout;
2490 USBI_GET_CONTEXT(ctx);
2491 r = get_next_timeout(ctx, tv, &poll_timeout);
2493 /* timeout already expired */
2494 return handle_timeouts(ctx);
2497 return handle_events(ctx, &poll_timeout);
2500 /** \ingroup libusb_poll
2501 * Determines whether your application must apply special timing considerations
2502 * when monitoring libusb's file descriptors.
2504 * This function is only useful for applications which retrieve and poll
2505 * libusb's file descriptors in their own main loop (\ref libusb_pollmain).
2507 * Ordinarily, libusb's event handler needs to be called into at specific
2508 * moments in time (in addition to times when there is activity on the file
2509 * descriptor set). The usual approach is to use libusb_get_next_timeout()
2510 * to learn about when the next timeout occurs, and to adjust your
2511 * poll()/select() timeout accordingly so that you can make a call into the
2512 * library at that time.
2514 * Some platforms supported by libusb do not come with this baggage - any
2515 * events relevant to timing will be represented by activity on the file
2516 * descriptor set, and libusb_get_next_timeout() will always return 0.
2517 * This function allows you to detect whether you are running on such a
2522 * \param ctx the context to operate on, or NULL for the default context
2523 * \returns 0 if you must call into libusb at times determined by
2524 * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
2525 * or through regular activity on the file descriptors.
2526 * \ref libusb_pollmain "Polling libusb file descriptors for event handling"
2528 int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
2530 #if defined(USBI_TIMERFD_AVAILABLE)
2531 USBI_GET_CONTEXT(ctx);
2532 return usbi_using_timerfd(ctx);
2539 /** \ingroup libusb_poll
2540 * Determine the next internal timeout that libusb needs to handle. You only
2541 * need to use this function if you are calling poll() or select() or similar
2542 * on libusb's file descriptors yourself - you do not need to use it if you
2543 * are calling libusb_handle_events() or a variant directly.
2545 * You should call this function in your main loop in order to determine how
2546 * long to wait for select() or poll() to return results. libusb needs to be
2547 * called into at this timeout, so you should use it as an upper bound on
2548 * your select() or poll() call.
2550 * When the timeout has expired, call into libusb_handle_events_timeout()
2551 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
2553 * This function may return 1 (success) and an all-zero timeval. If this is
2554 * the case, it indicates that libusb has a timeout that has already expired
2555 * so you should call libusb_handle_events_timeout() or similar immediately.
2556 * A return code of 0 indicates that there are no pending timeouts.
2558 * On some platforms, this function will always returns 0 (no pending
2559 * timeouts). See \ref polltime.
2561 * \param ctx the context to operate on, or NULL for the default context
2562 * \param tv output location for a relative time against the current
2563 * clock in which libusb must be called into in order to process timeout events
2564 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
2565 * or LIBUSB_ERROR_OTHER on failure
2567 int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
2570 struct usbi_transfer *transfer;
2571 struct timespec cur_ts;
2572 struct timeval cur_tv;
2573 struct timeval next_timeout = { 0, 0 };
2576 USBI_GET_CONTEXT(ctx);
2577 if (usbi_using_timerfd(ctx))
2580 usbi_mutex_lock(&ctx->flying_transfers_lock);
2581 if (list_empty(&ctx->flying_transfers)) {
2582 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2583 usbi_dbg("no URBs, no timeout!");
2587 /* find next transfer which hasn't already been processed as timed out */
2588 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2589 if (transfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2592 /* if we've reached transfers of infinte timeout, we're done looking */
2593 if (!timerisset(&transfer->timeout))
2596 next_timeout = transfer->timeout;
2599 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2601 if (!timerisset(&next_timeout)) {
2602 usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
2606 r = usbi_backend.clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
2608 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2611 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
2613 if (!timercmp(&cur_tv, &next_timeout, <)) {
2614 usbi_dbg("first timeout already expired");
2617 timersub(&next_timeout, &cur_tv, tv);
2618 usbi_dbg("next timeout in %ld.%06lds", (long)tv->tv_sec, (long)tv->tv_usec);
2624 /** \ingroup libusb_poll
2625 * Register notification functions for file descriptor additions/removals.
2626 * These functions will be invoked for every new or removed file descriptor
2627 * that libusb uses as an event source.
2629 * To remove notifiers, pass NULL values for the function pointers.
2631 * Note that file descriptors may have been added even before you register
2632 * these notifiers (e.g. at libusb_init() time).
2634 * Additionally, note that the removal notifier may be called during
2635 * libusb_exit() (e.g. when it is closing file descriptors that were opened
2636 * and added to the poll set at libusb_init() time). If you don't want this,
2637 * remove the notifiers immediately before calling libusb_exit().
2639 * \param ctx the context to operate on, or NULL for the default context
2640 * \param added_cb pointer to function for addition notifications
2641 * \param removed_cb pointer to function for removal notifications
2642 * \param user_data User data to be passed back to callbacks (useful for
2643 * passing context information)
2645 void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
2646 libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
2649 USBI_GET_CONTEXT(ctx);
2650 ctx->fd_added_cb = added_cb;
2651 ctx->fd_removed_cb = removed_cb;
2652 ctx->fd_cb_user_data = user_data;
2656 * Interrupt the iteration of the event handling thread, so that it picks
2657 * up the fd change. Callers of this function must hold the event_data_lock.
2659 static void usbi_fd_notification(struct libusb_context *ctx)
2663 /* Record that there is a new poll fd.
2664 * Only signal an event if there are no prior pending events. */
2665 pending_events = usbi_pending_events(ctx);
2666 ctx->event_flags |= USBI_EVENT_POLLFDS_MODIFIED;
2667 if (!pending_events)
2668 usbi_signal_event(ctx);
2671 /* Add a file descriptor to the list of file descriptors to be monitored.
2672 * events should be specified as a bitmask of events passed to poll(), e.g.
2673 * POLLIN and/or POLLOUT. */
2674 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
2676 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
2678 return LIBUSB_ERROR_NO_MEM;
2680 usbi_dbg("add fd %d events %d", fd, events);
2681 ipollfd->pollfd.fd = fd;
2682 ipollfd->pollfd.events = events;
2683 usbi_mutex_lock(&ctx->event_data_lock);
2684 list_add_tail(&ipollfd->list, &ctx->ipollfds);
2686 usbi_fd_notification(ctx);
2687 usbi_mutex_unlock(&ctx->event_data_lock);
2689 if (ctx->fd_added_cb)
2690 ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
2694 /* Remove a file descriptor from the list of file descriptors to be polled. */
2695 void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
2697 struct usbi_pollfd *ipollfd;
2700 usbi_dbg("remove fd %d", fd);
2701 usbi_mutex_lock(&ctx->event_data_lock);
2702 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd)
2703 if (ipollfd->pollfd.fd == fd) {
2709 usbi_dbg("couldn't find fd %d to remove", fd);
2710 usbi_mutex_unlock(&ctx->event_data_lock);
2714 list_del(&ipollfd->list);
2716 usbi_fd_notification(ctx);
2717 usbi_mutex_unlock(&ctx->event_data_lock);
2719 if (ctx->fd_removed_cb)
2720 ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
2723 /** \ingroup libusb_poll
2724 * Retrieve a list of file descriptors that should be polled by your main loop
2725 * as libusb event sources.
2727 * The returned list is NULL-terminated and should be freed with libusb_free_pollfds()
2728 * when done. The actual list contents must not be touched.
2730 * As file descriptors are a Unix-specific concept, this function is not
2731 * available on Windows and will always return NULL.
2733 * \param ctx the context to operate on, or NULL for the default context
2734 * \returns a NULL-terminated list of libusb_pollfd structures
2735 * \returns NULL on error
2736 * \returns NULL on platforms where the functionality is not available
2739 const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
2740 libusb_context *ctx)
2743 struct libusb_pollfd **ret = NULL;
2744 struct usbi_pollfd *ipollfd;
2746 USBI_GET_CONTEXT(ctx);
2748 usbi_mutex_lock(&ctx->event_data_lock);
2750 ret = calloc(ctx->pollfds_cnt + 1, sizeof(struct libusb_pollfd *));
2754 list_for_each_entry(ipollfd, &ctx->ipollfds, list, struct usbi_pollfd)
2755 ret[i++] = (struct libusb_pollfd *) ipollfd;
2756 ret[ctx->pollfds_cnt] = NULL;
2759 usbi_mutex_unlock(&ctx->event_data_lock);
2760 return (const struct libusb_pollfd **) ret;
2762 usbi_err(ctx, "external polling of libusb's internal descriptors "\
2763 "is not yet supported on Windows platforms");
2768 /** \ingroup libusb_poll
2769 * Free a list of libusb_pollfd structures. This should be called for all
2770 * pollfd lists allocated with libusb_get_pollfds().
2772 * Since version 1.0.20, \ref LIBUSB_API_VERSION >= 0x01000104
2774 * It is legal to call this function with a NULL pollfd list. In this case,
2775 * the function will simply do nothing.
2777 * \param pollfds the list of libusb_pollfd structures to free
2779 void API_EXPORTED libusb_free_pollfds(const struct libusb_pollfd **pollfds)
2781 free((void *)pollfds);
2784 /* Backends may call this from handle_events to report disconnection of a
2785 * device. This function ensures transfers get cancelled appropriately.
2786 * Callers of this function must hold the events_lock.
2788 void usbi_handle_disconnect(struct libusb_device_handle *dev_handle)
2790 struct usbi_transfer *cur;
2791 struct usbi_transfer *to_cancel;
2793 usbi_dbg("device %d.%d",
2794 dev_handle->dev->bus_number, dev_handle->dev->device_address);
2796 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
2799 * when we find a transfer for this device on the list, there are two
2800 * possible scenarios:
2801 * 1. the transfer is currently in-flight, in which case we terminate the
2803 * 2. the transfer has been added to the flying transfer list by
2804 * libusb_submit_transfer, has failed to submit and
2805 * libusb_submit_transfer is waiting for us to release the
2806 * flying_transfers_lock to remove it, so we ignore it
2811 usbi_mutex_lock(&HANDLE_CTX(dev_handle)->flying_transfers_lock);
2812 list_for_each_entry(cur, &HANDLE_CTX(dev_handle)->flying_transfers, list, struct usbi_transfer)
2813 if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == dev_handle) {
2814 usbi_mutex_lock(&cur->lock);
2815 if (cur->state_flags & USBI_TRANSFER_IN_FLIGHT)
2817 usbi_mutex_unlock(&cur->lock);
2822 usbi_mutex_unlock(&HANDLE_CTX(dev_handle)->flying_transfers_lock);
2827 usbi_dbg("cancelling transfer %p from disconnect",
2828 USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel));
2830 usbi_mutex_lock(&to_cancel->lock);
2831 usbi_backend.clear_transfer_priv(to_cancel);
2832 usbi_mutex_unlock(&to_cancel->lock);
2833 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);