1 /* -*- Mode: C; indent-tabs-mode:t ; c-basic-offset:8 -*- */
3 * I/O functions for libusb
4 * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
5 * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
6 * Copyright © 2019 Nathan Hjelm <hjelmn@cs.umm.edu>
7 * Copyright © 2019 Google LLC. All rights reserved.
9 * This library is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this library; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
30 * \page libusb_io Synchronous and asynchronous device I/O
32 * \section io_intro Introduction
34 * If you're using libusb in your application, you're probably wanting to
35 * perform I/O with devices - you want to perform USB data transfers.
37 * libusb offers two separate interfaces for device I/O. This page aims to
38 * introduce the two in order to help you decide which one is more suitable
39 * for your application. You can also choose to use both interfaces in your
40 * application by considering each transfer on a case-by-case basis.
42 * Once you have read through the following discussion, you should consult the
43 * detailed API documentation pages for the details:
44 * - \ref libusb_syncio
45 * - \ref libusb_asyncio
47 * \section theory Transfers at a logical level
49 * At a logical level, USB transfers typically happen in two parts. For
50 * example, when reading data from a endpoint:
51 * -# A request for data is sent to the device
52 * -# Some time later, the incoming data is received by the host
54 * or when writing data to an endpoint:
56 * -# The data is sent to the device
57 * -# Some time later, the host receives acknowledgement from the device that
58 * the data has been transferred.
60 * There may be an indefinite delay between the two steps. Consider a
61 * fictional USB input device with a button that the user can press. In order
62 * to determine when the button is pressed, you would likely submit a request
63 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
64 * Data will arrive when the button is pressed by the user, which is
65 * potentially hours later.
67 * libusb offers both a synchronous and an asynchronous interface to performing
68 * USB transfers. The main difference is that the synchronous interface
69 * combines both steps indicated above into a single function call, whereas
70 * the asynchronous interface separates them.
72 * \section sync The synchronous interface
74 * The synchronous I/O interface allows you to perform a USB transfer with
75 * a single function call. When the function call returns, the transfer has
76 * completed and you can parse the results.
78 * If you have used the libusb-0.1 before, this I/O style will seem familar to
79 * you. libusb-0.1 only offered a synchronous interface.
81 * In our input device example, to read button presses you might write code
82 * in the following style:
84 unsigned char data[4];
86 int r = libusb_bulk_transfer(dev_handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
87 if (r == 0 && actual_length == sizeof(data)) {
88 // results of the transaction can now be found in the data buffer
89 // parse them here and report button press
95 * The main advantage of this model is simplicity: you did everything with
96 * a single simple function call.
98 * However, this interface has its limitations. Your application will sleep
99 * inside libusb_bulk_transfer() until the transaction has completed. If it
100 * takes the user 3 hours to press the button, your application will be
101 * sleeping for that long. Execution will be tied up inside the library -
102 * the entire thread will be useless for that duration.
104 * Another issue is that by tieing up the thread with that single transaction
105 * there is no possibility of performing I/O with multiple endpoints and/or
106 * multiple devices simultaneously, unless you resort to creating one thread
109 * Additionally, there is no opportunity to cancel the transfer after the
110 * request has been submitted.
112 * For details on how to use the synchronous API, see the
113 * \ref libusb_syncio "synchronous I/O API documentation" pages.
115 * \section async The asynchronous interface
117 * Asynchronous I/O is the most significant new feature in libusb-1.0.
118 * Although it is a more complex interface, it solves all the issues detailed
121 * Instead of providing which functions that block until the I/O has complete,
122 * libusb's asynchronous interface presents non-blocking functions which
123 * begin a transfer and then return immediately. Your application passes a
124 * callback function pointer to this non-blocking function, which libusb will
125 * call with the results of the transaction when it has completed.
127 * Transfers which have been submitted through the non-blocking functions
128 * can be cancelled with a separate function call.
130 * The non-blocking nature of this interface allows you to be simultaneously
131 * performing I/O to multiple endpoints on multiple devices, without having
134 * This added flexibility does come with some complications though:
135 * - In the interest of being a lightweight library, libusb does not create
136 * threads and can only operate when your application is calling into it. Your
137 * application must call into libusb from it's main loop when events are ready
138 * to be handled, or you must use some other scheme to allow libusb to
139 * undertake whatever work needs to be done.
140 * - libusb also needs to be called into at certain fixed points in time in
141 * order to accurately handle transfer timeouts.
142 * - Memory handling becomes more complex. You cannot use stack memory unless
143 * the function with that stack is guaranteed not to return until the transfer
144 * callback has finished executing.
145 * - You generally lose some linearity from your code flow because submitting
146 * the transfer request is done in a separate function from where the transfer
147 * results are handled. This becomes particularly obvious when you want to
148 * submit a second transfer based on the results of an earlier transfer.
150 * Internally, libusb's synchronous interface is expressed in terms of function
151 * calls to the asynchronous interface.
153 * For details on how to use the asynchronous API, see the
154 * \ref libusb_asyncio "asynchronous I/O API" documentation pages.
159 * \page libusb_packetoverflow Packets and overflows
161 * \section packets Packet abstraction
163 * The USB specifications describe how data is transmitted in packets, with
164 * constraints on packet size defined by endpoint descriptors. The host must
165 * not send data payloads larger than the endpoint's maximum packet size.
167 * libusb and the underlying OS abstract out the packet concept, allowing you
168 * to request transfers of any size. Internally, the request will be divided
169 * up into correctly-sized packets. You do not have to be concerned with
170 * packet sizes, but there is one exception when considering overflows.
172 * \section overflow Bulk/interrupt transfer overflows
174 * When requesting data on a bulk endpoint, libusb requires you to supply a
175 * buffer and the maximum number of bytes of data that libusb can put in that
176 * buffer. However, the size of the buffer is not communicated to the device -
177 * the device is just asked to send any amount of data.
179 * There is no problem if the device sends an amount of data that is less than
180 * or equal to the buffer size. libusb reports this condition to you through
181 * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
184 * Problems may occur if the device attempts to send more data than can fit in
185 * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
186 * other behaviour is largely undefined: actual_length may or may not be
187 * accurate, the chunk of data that can fit in the buffer (before overflow)
188 * may or may not have been transferred.
190 * Overflows are nasty, but can be avoided. Even though you were told to
191 * ignore packets above, think about the lower level details: each transfer is
192 * split into packets (typically small, with a maximum size of 512 bytes).
193 * Overflows can only happen if the final packet in an incoming data transfer
194 * is smaller than the actual packet that the device wants to transfer.
195 * Therefore, you will never see an overflow if your transfer buffer size is a
196 * multiple of the endpoint's packet size: the final packet will either
197 * fill up completely or will be only partially filled.
201 * @defgroup libusb_asyncio Asynchronous device I/O
203 * This page details libusb's asynchronous (non-blocking) API for USB device
204 * I/O. This interface is very powerful but is also quite complex - you will
205 * need to read this page carefully to understand the necessary considerations
206 * and issues surrounding use of this interface. Simplistic applications
207 * may wish to consider the \ref libusb_syncio "synchronous I/O API" instead.
209 * The asynchronous interface is built around the idea of separating transfer
210 * submission and handling of transfer completion (the synchronous model
211 * combines both of these into one). There may be a long delay between
212 * submission and completion, however the asynchronous submission function
213 * is non-blocking so will return control to your application during that
214 * potentially long delay.
216 * \section asyncabstraction Transfer abstraction
218 * For the asynchronous I/O, libusb implements the concept of a generic
219 * transfer entity for all types of I/O (control, bulk, interrupt,
220 * isochronous). The generic transfer object must be treated slightly
221 * differently depending on which type of I/O you are performing with it.
223 * This is represented by the public libusb_transfer structure type.
225 * \section asynctrf Asynchronous transfers
227 * We can view asynchronous I/O as a 5 step process:
228 * -# <b>Allocation</b>: allocate a libusb_transfer
229 * -# <b>Filling</b>: populate the libusb_transfer instance with information
230 * about the transfer you wish to perform
231 * -# <b>Submission</b>: ask libusb to submit the transfer
232 * -# <b>Completion handling</b>: examine transfer results in the
233 * libusb_transfer structure
234 * -# <b>Deallocation</b>: clean up resources
237 * \subsection asyncalloc Allocation
239 * This step involves allocating memory for a USB transfer. This is the
240 * generic transfer object mentioned above. At this stage, the transfer
241 * is "blank" with no details about what type of I/O it will be used for.
243 * Allocation is done with the libusb_alloc_transfer() function. You must use
244 * this function rather than allocating your own transfers.
246 * \subsection asyncfill Filling
248 * This step is where you take a previously allocated transfer and fill it
249 * with information to determine the message type and direction, data buffer,
250 * callback function, etc.
252 * You can either fill the required fields yourself or you can use the
253 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
254 * and libusb_fill_interrupt_transfer().
256 * \subsection asyncsubmit Submission
258 * When you have allocated a transfer and filled it, you can submit it using
259 * libusb_submit_transfer(). This function returns immediately but can be
260 * regarded as firing off the I/O request in the background.
262 * \subsection asynccomplete Completion handling
264 * After a transfer has been submitted, one of four things can happen to it:
266 * - The transfer completes (i.e. some data was transferred)
267 * - The transfer has a timeout and the timeout expires before all data is
269 * - The transfer fails due to an error
270 * - The transfer is cancelled
272 * Each of these will cause the user-specified transfer callback function to
273 * be invoked. It is up to the callback function to determine which of the
274 * above actually happened and to act accordingly.
276 * The user-specified callback is passed a pointer to the libusb_transfer
277 * structure which was used to setup and submit the transfer. At completion
278 * time, libusb has populated this structure with results of the transfer:
279 * success or failure reason, number of bytes of data transferred, etc. See
280 * the libusb_transfer structure documentation for more information.
282 * <b>Important Note</b>: The user-specified callback is called from an event
283 * handling context. It is therefore important that no calls are made into
284 * libusb that will attempt to perform any event handling. Examples of such
285 * functions are any listed in the \ref libusb_syncio "synchronous API" and any of
286 * the blocking functions that retrieve \ref libusb_desc "USB descriptors".
288 * \subsection Deallocation
290 * When a transfer has completed (i.e. the callback function has been invoked),
291 * you are advised to free the transfer (unless you wish to resubmit it, see
292 * below). Transfers are deallocated with libusb_free_transfer().
294 * It is undefined behaviour to free a transfer which has not completed.
296 * \section asyncresubmit Resubmission
298 * You may be wondering why allocation, filling, and submission are all
299 * separated above where they could reasonably be combined into a single
302 * The reason for separation is to allow you to resubmit transfers without
303 * having to allocate new ones every time. This is especially useful for
304 * common situations dealing with interrupt endpoints - you allocate one
305 * transfer, fill and submit it, and when it returns with results you just
306 * resubmit it for the next interrupt.
308 * \section asynccancel Cancellation
310 * Another advantage of using the asynchronous interface is that you have
311 * the ability to cancel transfers which have not yet completed. This is
312 * done by calling the libusb_cancel_transfer() function.
314 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
315 * cancellation actually completes, the transfer's callback function will
316 * be invoked, and the callback function should check the transfer status to
317 * determine that it was cancelled.
319 * Freeing the transfer after it has been cancelled but before cancellation
320 * has completed will result in undefined behaviour.
322 * When a transfer is cancelled, some of the data may have been transferred.
323 * libusb will communicate this to you in the transfer callback. Do not assume
324 * that no data was transferred.
326 * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
328 * If your device does not have predictable transfer sizes (or it misbehaves),
329 * your application may submit a request for data on an IN endpoint which is
330 * smaller than the data that the device wishes to send. In some circumstances
331 * this will cause an overflow, which is a nasty condition to deal with. See
332 * the \ref libusb_packetoverflow page for discussion.
334 * \section asyncctrl Considerations for control transfers
336 * The <tt>libusb_transfer</tt> structure is generic and hence does not
337 * include specific fields for the control-specific setup packet structure.
339 * In order to perform a control transfer, you must place the 8-byte setup
340 * packet at the start of the data buffer. To simplify this, you could
341 * cast the buffer pointer to type struct libusb_control_setup, or you can
342 * use the helper function libusb_fill_control_setup().
344 * The wLength field placed in the setup packet must be the length you would
345 * expect to be sent in the setup packet: the length of the payload that
346 * follows (or the expected maximum number of bytes to receive). However,
347 * the length field of the libusb_transfer object must be the length of
348 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
349 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
351 * If you use the helper functions, this is simplified for you:
352 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
353 * data you are sending/requesting.
354 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
355 * request size as the wLength value (i.e. do not include the extra space you
356 * allocated for the control setup).
357 * -# If this is a host-to-device transfer, place the data to be transferred
358 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
359 * -# Call libusb_fill_control_transfer() to associate the data buffer with
360 * the transfer (and to set the remaining details such as callback and timeout).
361 * - Note that there is no parameter to set the length field of the transfer.
362 * The length is automatically inferred from the wLength field of the setup
364 * -# Submit the transfer.
366 * The multi-byte control setup fields (wValue, wIndex and wLength) must
367 * be given in little-endian byte order (the endianness of the USB bus).
368 * Endianness conversion is transparently handled by
369 * libusb_fill_control_setup() which is documented to accept host-endian
372 * Further considerations are needed when handling transfer completion in
373 * your callback function:
374 * - As you might expect, the setup packet will still be sitting at the start
375 * of the data buffer.
376 * - If this was a device-to-host transfer, the received data will be sitting
377 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
378 * - The actual_length field of the transfer structure is relative to the
379 * wLength of the setup packet, rather than the size of the data buffer. So,
380 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
381 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
382 * transferred in entirity.
384 * To simplify parsing of setup packets and obtaining the data from the
385 * correct offset, you may wish to use the libusb_control_transfer_get_data()
386 * and libusb_control_transfer_get_setup() functions within your transfer
389 * Even though control endpoints do not halt, a completed control transfer
390 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
391 * request was not supported.
393 * \section asyncintr Considerations for interrupt transfers
395 * All interrupt transfers are performed using the polling interval presented
396 * by the bInterval value of the endpoint descriptor.
398 * \section asynciso Considerations for isochronous transfers
400 * Isochronous transfers are more complicated than transfers to
401 * non-isochronous endpoints.
403 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
404 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
406 * During filling, set \ref libusb_transfer::type "type" to
407 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
408 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
409 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
410 * or equal to the number of packets you requested during allocation.
411 * libusb_alloc_transfer() does not set either of these fields for you, given
412 * that you might not even use the transfer on an isochronous endpoint.
414 * Next, populate the length field for the first num_iso_packets entries in
415 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
416 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
417 * packet length is determined by the wMaxPacketSize field in the endpoint
419 * Two functions can help you here:
421 * - libusb_get_max_iso_packet_size() is an easy way to determine the max
422 * packet size for an isochronous endpoint. Note that the maximum packet
423 * size is actually the maximum number of bytes that can be transmitted in
424 * a single microframe, therefore this function multiplies the maximum number
425 * of bytes per transaction by the number of transaction opportunities per
427 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
428 * within a transfer, which is usually what you want.
430 * For outgoing transfers, you'll obviously fill the buffer and populate the
431 * packet descriptors in hope that all the data gets transferred. For incoming
432 * transfers, you must ensure the buffer has sufficient capacity for
433 * the situation where all packets transfer the full amount of requested data.
435 * Completion handling requires some extra consideration. The
436 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
437 * is meaningless and should not be examined; instead you must refer to the
438 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
439 * each individual packet.
441 * The \ref libusb_transfer::status "status" field of the transfer is also a
443 * - If the packets were submitted and the isochronous data microframes
444 * completed normally, status will have value
445 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
446 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
447 * delays are not counted as transfer errors; the transfer.status field may
448 * indicate COMPLETED even if some or all of the packets failed. Refer to
449 * the \ref libusb_iso_packet_descriptor::status "status" field of each
450 * individual packet to determine packet failures.
451 * - The status field will have value
452 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
453 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
454 * - Other transfer status codes occur with normal behaviour.
456 * The data for each packet will be found at an offset into the buffer that
457 * can be calculated as if each prior packet completed in full. The
458 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
459 * functions may help you here.
461 * \section asynclimits Transfer length limitations
463 * Some operating systems may impose limits on the length of the transfer data
464 * buffer or, in the case of isochronous transfers, the length of individual
465 * isochronous packets. Such limits can be difficult for libusb to detect, so
466 * in most cases the library will simply try and submit the transfer as set up
467 * by you. If the transfer fails to submit because it is too large,
468 * libusb_submit_transfer() will return
469 * \ref libusb_error::LIBUSB_ERROR_INVALID_PARAM "LIBUSB_ERROR_INVALID_PARAM".
471 * The following are known limits for control transfer lengths. Note that this
472 * length includes the 8-byte setup packet.
473 * - Linux (4,096 bytes)
474 * - Windows (4,096 bytes)
476 * \section asyncmem Memory caveats
478 * In most circumstances, it is not safe to use stack memory for transfer
479 * buffers. This is because the function that fired off the asynchronous
480 * transfer may return before libusb has finished using the buffer, and when
481 * the function returns it's stack gets destroyed. This is true for both
482 * host-to-device and device-to-host transfers.
484 * The only case in which it is safe to use stack memory is where you can
485 * guarantee that the function owning the stack space for the buffer does not
486 * return until after the transfer's callback function has completed. In every
487 * other case, you need to use heap memory instead.
489 * \section asyncflags Fine control
491 * Through using this asynchronous interface, you may find yourself repeating
492 * a few simple operations many times. You can apply a bitwise OR of certain
493 * flags to a transfer to simplify certain things:
494 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
495 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
496 * less than the requested amount of data being marked with status
497 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
498 * (they would normally be regarded as COMPLETED)
499 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
500 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
501 * buffer when freeing the transfer.
502 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
503 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
504 * transfer after the transfer callback returns.
506 * \section asyncevent Event handling
508 * An asynchronous model requires that libusb perform work at various
509 * points in time - namely processing the results of previously-submitted
510 * transfers and invoking the user-supplied callback function.
512 * This gives rise to the libusb_handle_events() function which your
513 * application must call into when libusb has work do to. This gives libusb
514 * the opportunity to reap pending transfers, invoke callbacks, etc.
516 * There are 2 different approaches to dealing with libusb_handle_events:
518 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
520 * -# Integrate libusb with your application's main event loop. libusb
521 * exposes a set of file descriptors which allow you to do this.
523 * The first approach has the big advantage that it will also work on Windows
524 * were libusb' poll API for select / poll integration is not available. So
525 * if you want to support Windows and use the async API, you must use this
526 * approach, see the \ref eventthread "Using an event handling thread" section
529 * If you prefer a single threaded approach with a single central event loop,
530 * see the \ref libusb_poll "polling and timing" section for how to integrate libusb
531 * into your application's main event loop.
533 * \section eventthread Using an event handling thread
535 * Lets begin with stating the obvious: If you're going to use a separate
536 * thread for libusb event handling, your callback functions MUST be
539 * Other then that doing event handling from a separate thread, is mostly
540 * simple. You can use an event thread function as follows:
542 void *event_thread_func(void *ctx)
544 while (event_thread_run)
545 libusb_handle_events(ctx);
551 * There is one caveat though, stopping this thread requires setting the
552 * event_thread_run variable to 0, and after that libusb_handle_events() needs
553 * to return control to event_thread_func. But unless some event happens,
554 * libusb_handle_events() will not return.
556 * There are 2 different ways of dealing with this, depending on if your
557 * application uses libusb' \ref libusb_hotplug "hotplug" support or not.
559 * Applications which do not use hotplug support, should not start the event
560 * thread until after their first call to libusb_open(), and should stop the
561 * thread when closing the last open device as follows:
563 void my_close_handle(libusb_device_handle *dev_handle)
566 event_thread_run = 0;
568 libusb_close(dev_handle); // This wakes up libusb_handle_events()
571 pthread_join(event_thread);
577 * Applications using hotplug support should start the thread at program init,
578 * after having successfully called libusb_hotplug_register_callback(), and
579 * should stop the thread at program exit as follows:
581 void my_libusb_exit(void)
583 event_thread_run = 0;
584 libusb_hotplug_deregister_callback(ctx, hotplug_cb_handle); // This wakes up libusb_handle_events()
585 pthread_join(event_thread);
592 * @defgroup libusb_poll Polling and timing
594 * This page documents libusb's functions for polling events and timing.
595 * These functions are only necessary for users of the
596 * \ref libusb_asyncio "asynchronous API". If you are only using the simpler
597 * \ref libusb_syncio "synchronous API" then you do not need to ever call these
600 * The justification for the functionality described here has already been
601 * discussed in the \ref asyncevent "event handling" section of the
602 * asynchronous API documentation. In summary, libusb does not create internal
603 * threads for event processing and hence relies on your application calling
604 * into libusb at certain points in time so that pending events can be handled.
606 * Your main loop is probably already calling poll() or select() or a
607 * variant on a set of file descriptors for other event sources (e.g. keyboard
608 * button presses, mouse movements, network sockets, etc). You then add
609 * libusb's file descriptors to your poll()/select() calls, and when activity
610 * is detected on such descriptors you know it is time to call
611 * libusb_handle_events().
613 * There is one final event handling complication. libusb supports
614 * asynchronous transfers which time out after a specified time period.
616 * On some platforms a timerfd is used, so the timeout handling is just another
617 * fd, on other platforms this requires that libusb is called into at or after
618 * the timeout to handle it. So, in addition to considering libusb's file
619 * descriptors in your main event loop, you must also consider that libusb
620 * sometimes needs to be called into at fixed points in time even when there
621 * is no file descriptor activity, see \ref polltime details.
623 * In order to know precisely when libusb needs to be called into, libusb
624 * offers you a set of pollable file descriptors and information about when
625 * the next timeout expires.
627 * If you are using the asynchronous I/O API, you must take one of the two
628 * following options, otherwise your I/O will not complete.
630 * \section pollsimple The simple option
632 * If your application revolves solely around libusb and does not need to
633 * handle other event sources, you can have a program structure as follows:
636 // find and open device
637 // maybe fire off some initial async I/O
639 while (user_has_not_requested_exit)
640 libusb_handle_events(ctx);
645 * With such a simple main loop, you do not have to worry about managing
646 * sets of file descriptors or handling timeouts. libusb_handle_events() will
647 * handle those details internally.
649 * \section libusb_pollmain The more advanced option
651 * \note This functionality is currently only available on Unix-like platforms.
652 * On Windows, libusb_get_pollfds() simply returns NULL. Applications which
653 * want to support Windows are advised to use an \ref eventthread
654 * "event handling thread" instead.
656 * In more advanced applications, you will already have a main loop which
657 * is monitoring other event sources: network sockets, X11 events, mouse
658 * movements, etc. Through exposing a set of file descriptors, libusb is
659 * designed to cleanly integrate into such main loops.
661 * In addition to polling file descriptors for the other event sources, you
662 * take a set of file descriptors from libusb and monitor those too. When you
663 * detect activity on libusb's file descriptors, you call
664 * libusb_handle_events_timeout() in non-blocking mode.
666 * What's more, libusb may also need to handle events at specific moments in
667 * time. No file descriptor activity is generated at these times, so your
668 * own application needs to be continually aware of when the next one of these
669 * moments occurs (through calling libusb_get_next_timeout()), and then it
670 * needs to call libusb_handle_events_timeout() in non-blocking mode when
671 * these moments occur. This means that you need to adjust your
672 * poll()/select() timeout accordingly.
674 * libusb provides you with a set of file descriptors to poll and expects you
675 * to poll all of them, treating them as a single entity. The meaning of each
676 * file descriptor in the set is an internal implementation detail,
677 * platform-dependent and may vary from release to release. Don't try and
678 * interpret the meaning of the file descriptors, just do as libusb indicates,
679 * polling all of them at once.
681 * In pseudo-code, you want something that looks like:
685 libusb_get_pollfds(ctx)
686 while (user has not requested application exit) {
687 libusb_get_next_timeout(ctx);
688 poll(on libusb file descriptors plus any other event sources of interest,
689 using a timeout no larger than the value libusb just suggested)
690 if (poll() indicated activity on libusb file descriptors)
691 libusb_handle_events_timeout(ctx, &zero_tv);
692 if (time has elapsed to or beyond the libusb timeout)
693 libusb_handle_events_timeout(ctx, &zero_tv);
694 // handle events from other sources here
700 * \subsection polltime Notes on time-based events
702 * The above complication with having to track time and call into libusb at
703 * specific moments is a bit of a headache. For maximum compatibility, you do
704 * need to write your main loop as above, but you may decide that you can
705 * restrict the supported platforms of your application and get away with
706 * a more simplistic scheme.
708 * These time-based event complications are \b not required on the following
711 * - Linux, provided that the following version requirements are satisfied:
712 * - Linux v2.6.27 or newer, compiled with timerfd support
713 * - glibc v2.9 or newer
714 * - libusb v1.0.5 or newer
716 * Under these configurations, libusb_get_next_timeout() will \em always return
717 * 0, so your main loop can be simplified to:
721 libusb_get_pollfds(ctx)
722 while (user has not requested application exit) {
723 poll(on libusb file descriptors plus any other event sources of interest,
724 using any timeout that you like)
725 if (poll() indicated activity on libusb file descriptors)
726 libusb_handle_events_timeout(ctx, &zero_tv);
727 // handle events from other sources here
733 * Do remember that if you simplify your main loop to the above, you will
734 * lose compatibility with some platforms (including legacy Linux platforms,
735 * and <em>any future platforms supported by libusb which may have time-based
736 * event requirements</em>). The resultant problems will likely appear as
737 * strange bugs in your application.
739 * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
740 * check to see if it is safe to ignore the time-based event complications.
741 * If your application has taken the shortcut of ignoring libusb's next timeout
742 * in your main loop, then you are advised to check the return value of
743 * libusb_pollfds_handle_timeouts() during application startup, and to abort
744 * if the platform does suffer from these timing complications.
746 * \subsection fdsetchange Changes in the file descriptor set
748 * The set of file descriptors that libusb uses as event sources may change
749 * during the life of your application. Rather than having to repeatedly
750 * call libusb_get_pollfds(), you can set up notification functions for when
751 * the file descriptor set changes using libusb_set_pollfd_notifiers().
753 * \subsection mtissues Multi-threaded considerations
755 * Unfortunately, the situation is complicated further when multiple threads
756 * come into play. If two threads are monitoring the same file descriptors,
757 * the fact that only one thread will be woken up when an event occurs causes
760 * The events lock, event waiters lock, and libusb_handle_events_locked()
761 * entities are added to solve these problems. You do not need to be concerned
762 * with these entities otherwise.
764 * See the extra documentation: \ref libusb_mtasync
767 /** \page libusb_mtasync Multi-threaded applications and asynchronous I/O
769 * libusb is a thread-safe library, but extra considerations must be applied
770 * to applications which interact with libusb from multiple threads.
772 * The underlying issue that must be addressed is that all libusb I/O
773 * revolves around monitoring file descriptors through the poll()/select()
774 * system calls. This is directly exposed at the
775 * \ref libusb_asyncio "asynchronous interface" but it is important to note that the
776 * \ref libusb_syncio "synchronous interface" is implemented on top of the
777 * asynchonrous interface, therefore the same considerations apply.
779 * The issue is that if two or more threads are concurrently calling poll()
780 * or select() on libusb's file descriptors then only one of those threads
781 * will be woken up when an event arrives. The others will be completely
782 * oblivious that anything has happened.
784 * Consider the following pseudo-code, which submits an asynchronous transfer
785 * then waits for its completion. This style is one way you could implement a
786 * synchronous interface on top of the asynchronous interface (and libusb
787 * does something similar, albeit more advanced due to the complications
788 * explained on this page).
791 void cb(struct libusb_transfer *transfer)
793 int *completed = transfer->user_data;
798 struct libusb_transfer *transfer;
799 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE] __attribute__ ((aligned (2)));
802 transfer = libusb_alloc_transfer(0);
803 libusb_fill_control_setup(buffer,
804 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
805 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
806 libusb_submit_transfer(transfer);
809 poll(libusb file descriptors, 120*1000);
810 if (poll indicates activity)
811 libusb_handle_events_timeout(ctx, &zero_tv);
813 printf("completed!");
818 * Here we are <em>serializing</em> completion of an asynchronous event
819 * against a condition - the condition being completion of a specific transfer.
820 * The poll() loop has a long timeout to minimize CPU usage during situations
821 * when nothing is happening (it could reasonably be unlimited).
823 * If this is the only thread that is polling libusb's file descriptors, there
824 * is no problem: there is no danger that another thread will swallow up the
825 * event that we are interested in. On the other hand, if there is another
826 * thread polling the same descriptors, there is a chance that it will receive
827 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
828 * will only realise that the transfer has completed on the next iteration of
829 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
830 * undesirable, and don't even think about using short timeouts to circumvent
833 * The solution here is to ensure that no two threads are ever polling the
834 * file descriptors at the same time. A naive implementation of this would
835 * impact the capabilities of the library, so libusb offers the scheme
836 * documented below to ensure no loss of functionality.
838 * Before we go any further, it is worth mentioning that all libusb-wrapped
839 * event handling procedures fully adhere to the scheme documented below.
840 * This includes libusb_handle_events() and its variants, and all the
841 * synchronous I/O functions - libusb hides this headache from you.
843 * \section Using libusb_handle_events() from multiple threads
845 * Even when only using libusb_handle_events() and synchronous I/O functions,
846 * you can still have a race condition. You might be tempted to solve the
847 * above with libusb_handle_events() like so:
850 libusb_submit_transfer(transfer);
853 libusb_handle_events(ctx);
855 printf("completed!");
858 * This however has a race between the checking of completed and
859 * libusb_handle_events() acquiring the events lock, so another thread
860 * could have completed the transfer, resulting in this thread hanging
861 * until either a timeout or another event occurs. See also commit
862 * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
863 * synchronous API implementation of libusb.
865 * Fixing this race requires checking the variable completed only after
866 * taking the event lock, which defeats the concept of just calling
867 * libusb_handle_events() without worrying about locking. This is why
868 * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
869 * and libusb_handle_events_completed() functions, which handles doing the
870 * completion check for you after they have acquired the lock:
873 libusb_submit_transfer(transfer);
876 libusb_handle_events_completed(ctx, &completed);
878 printf("completed!");
881 * This nicely fixes the race in our example. Note that if all you want to
882 * do is submit a single transfer and wait for its completion, then using
883 * one of the synchronous I/O functions is much easier.
885 * \section eventlock The events lock
887 * The problem is when we consider the fact that libusb exposes file
888 * descriptors to allow for you to integrate asynchronous USB I/O into
889 * existing main loops, effectively allowing you to do some work behind
890 * libusb's back. If you do take libusb's file descriptors and pass them to
891 * poll()/select() yourself, you need to be aware of the associated issues.
893 * The first concept to be introduced is the events lock. The events lock
894 * is used to serialize threads that want to handle events, such that only
895 * one thread is handling events at any one time.
897 * You must take the events lock before polling libusb file descriptors,
898 * using libusb_lock_events(). You must release the lock as soon as you have
899 * aborted your poll()/select() loop, using libusb_unlock_events().
901 * \section threadwait Letting other threads do the work for you
903 * Although the events lock is a critical part of the solution, it is not
904 * enough on it's own. You might wonder if the following is sufficient...
906 libusb_lock_events(ctx);
908 poll(libusb file descriptors, 120*1000);
909 if (poll indicates activity)
910 libusb_handle_events_timeout(ctx, &zero_tv);
912 libusb_unlock_events(ctx);
914 * ...and the answer is that it is not. This is because the transfer in the
915 * code shown above may take a long time (say 30 seconds) to complete, and
916 * the lock is not released until the transfer is completed.
918 * Another thread with similar code that wants to do event handling may be
919 * working with a transfer that completes after a few milliseconds. Despite
920 * having such a quick completion time, the other thread cannot check that
921 * status of its transfer until the code above has finished (30 seconds later)
922 * due to contention on the lock.
924 * To solve this, libusb offers you a mechanism to determine when another
925 * thread is handling events. It also offers a mechanism to block your thread
926 * until the event handling thread has completed an event (and this mechanism
927 * does not involve polling of file descriptors).
929 * After determining that another thread is currently handling events, you
930 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
931 * You then re-check that some other thread is still handling events, and if
932 * so, you call libusb_wait_for_event().
934 * libusb_wait_for_event() puts your application to sleep until an event
935 * occurs, or until a thread releases the events lock. When either of these
936 * things happen, your thread is woken up, and should re-check the condition
937 * it was waiting on. It should also re-check that another thread is handling
938 * events, and if not, it should start handling events itself.
940 * This looks like the following, as pseudo-code:
943 if (libusb_try_lock_events(ctx) == 0) {
944 // we obtained the event lock: do our own event handling
946 if (!libusb_event_handling_ok(ctx)) {
947 libusb_unlock_events(ctx);
950 poll(libusb file descriptors, 120*1000);
951 if (poll indicates activity)
952 libusb_handle_events_locked(ctx, 0);
954 libusb_unlock_events(ctx);
956 // another thread is doing event handling. wait for it to signal us that
957 // an event has completed
958 libusb_lock_event_waiters(ctx);
961 // now that we have the event waiters lock, double check that another
962 // thread is still handling events for us. (it may have ceased handling
963 // events in the time it took us to reach this point)
964 if (!libusb_event_handler_active(ctx)) {
965 // whoever was handling events is no longer doing so, try again
966 libusb_unlock_event_waiters(ctx);
970 libusb_wait_for_event(ctx, NULL);
972 libusb_unlock_event_waiters(ctx);
974 printf("completed!\n");
977 * A naive look at the above code may suggest that this can only support
978 * one event waiter (hence a total of 2 competing threads, the other doing
979 * event handling), because the event waiter seems to have taken the event
980 * waiters lock while waiting for an event. However, the system does support
981 * multiple event waiters, because libusb_wait_for_event() actually drops
982 * the lock while waiting, and reaquires it before continuing.
984 * We have now implemented code which can dynamically handle situations where
985 * nobody is handling events (so we should do it ourselves), and it can also
986 * handle situations where another thread is doing event handling (so we can
987 * piggyback onto them). It is also equipped to handle a combination of
988 * the two, for example, another thread is doing event handling, but for
989 * whatever reason it stops doing so before our condition is met, so we take
990 * over the event handling.
992 * Four functions were introduced in the above pseudo-code. Their importance
993 * should be apparent from the code shown above.
994 * -# libusb_try_lock_events() is a non-blocking function which attempts
995 * to acquire the events lock but returns a failure code if it is contended.
996 * -# libusb_event_handling_ok() checks that libusb is still happy for your
997 * thread to be performing event handling. Sometimes, libusb needs to
998 * interrupt the event handler, and this is how you can check if you have
999 * been interrupted. If this function returns 0, the correct behaviour is
1000 * for you to give up the event handling lock, and then to repeat the cycle.
1001 * The following libusb_try_lock_events() will fail, so you will become an
1002 * events waiter. For more information on this, read \ref fullstory below.
1003 * -# libusb_handle_events_locked() is a variant of
1004 * libusb_handle_events_timeout() that you can call while holding the
1005 * events lock. libusb_handle_events_timeout() itself implements similar
1006 * logic to the above, so be sure not to call it when you are
1007 * "working behind libusb's back", as is the case here.
1008 * -# libusb_event_handler_active() determines if someone is currently
1009 * holding the events lock
1011 * You might be wondering why there is no function to wake up all threads
1012 * blocked on libusb_wait_for_event(). This is because libusb can do this
1013 * internally: it will wake up all such threads when someone calls
1014 * libusb_unlock_events() or when a transfer completes (at the point after its
1015 * callback has returned).
1017 * \subsection fullstory The full story
1019 * The above explanation should be enough to get you going, but if you're
1020 * really thinking through the issues then you may be left with some more
1021 * questions regarding libusb's internals. If you're curious, read on, and if
1022 * not, skip to the next section to avoid confusing yourself!
1024 * The immediate question that may spring to mind is: what if one thread
1025 * modifies the set of file descriptors that need to be polled while another
1026 * thread is doing event handling?
1028 * There are 2 situations in which this may happen.
1029 * -# libusb_open() will add another file descriptor to the poll set,
1030 * therefore it is desirable to interrupt the event handler so that it
1031 * restarts, picking up the new descriptor.
1032 * -# libusb_close() will remove a file descriptor from the poll set. There
1033 * are all kinds of race conditions that could arise here, so it is
1034 * important that nobody is doing event handling at this time.
1036 * libusb handles these issues internally, so application developers do not
1037 * have to stop their event handlers while opening/closing devices. Here's how
1038 * it works, focusing on the libusb_close() situation first:
1040 * -# During initialization, libusb opens an internal pipe, and it adds the read
1041 * end of this pipe to the set of file descriptors to be polled.
1042 * -# During libusb_close(), libusb writes some dummy data on this event pipe.
1043 * This immediately interrupts the event handler. libusb also records
1044 * internally that it is trying to interrupt event handlers for this
1045 * high-priority event.
1046 * -# At this point, some of the functions described above start behaving
1048 * - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
1049 * OK for event handling to continue.
1050 * - libusb_try_lock_events() starts returning 1, indicating that another
1051 * thread holds the event handling lock, even if the lock is uncontended.
1052 * - libusb_event_handler_active() starts returning 1, indicating that
1053 * another thread is doing event handling, even if that is not true.
1054 * -# The above changes in behaviour result in the event handler stopping and
1055 * giving up the events lock very quickly, giving the high-priority
1056 * libusb_close() operation a "free ride" to acquire the events lock. All
1057 * threads that are competing to do event handling become event waiters.
1058 * -# With the events lock held inside libusb_close(), libusb can safely remove
1059 * a file descriptor from the poll set, in the safety of knowledge that
1060 * nobody is polling those descriptors or trying to access the poll set.
1061 * -# After obtaining the events lock, the close operation completes very
1062 * quickly (usually a matter of milliseconds) and then immediately releases
1064 * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
1065 * reverts to the original, documented behaviour.
1066 * -# The release of the events lock causes the threads that are waiting for
1067 * events to be woken up and to start competing to become event handlers
1068 * again. One of them will succeed; it will then re-obtain the list of poll
1069 * descriptors, and USB I/O will then continue as normal.
1071 * libusb_open() is similar, and is actually a more simplistic case. Upon a
1072 * call to libusb_open():
1074 * -# The device is opened and a file descriptor is added to the poll set.
1075 * -# libusb sends some dummy data on the event pipe, and records that it
1076 * is trying to modify the poll descriptor set.
1077 * -# The event handler is interrupted, and the same behaviour change as for
1078 * libusb_close() takes effect, causing all event handling threads to become
1080 * -# The libusb_open() implementation takes its free ride to the events lock.
1081 * -# Happy that it has successfully paused the events handler, libusb_open()
1082 * releases the events lock.
1083 * -# The event waiter threads are all woken up and compete to become event
1084 * handlers again. The one that succeeds will obtain the list of poll
1085 * descriptors again, which will include the addition of the new device.
1087 * \subsection concl Closing remarks
1089 * The above may seem a little complicated, but hopefully I have made it clear
1090 * why such complications are necessary. Also, do not forget that this only
1091 * applies to applications that take libusb's file descriptors and integrate
1092 * them into their own polling loops.
1094 * You may decide that it is OK for your multi-threaded application to ignore
1095 * some of the rules and locks detailed above, because you don't think that
1096 * two threads can ever be polling the descriptors at the same time. If that
1097 * is the case, then that's good news for you because you don't have to worry.
1098 * But be careful here; remember that the synchronous I/O functions do event
1099 * handling internally. If you have one thread doing event handling in a loop
1100 * (without implementing the rules and locking semantics documented above)
1101 * and another trying to send a synchronous USB transfer, you will end up with
1102 * two threads monitoring the same descriptors, and the above-described
1103 * undesirable behaviour occurring. The solution is for your polling thread to
1104 * play by the rules; the synchronous I/O functions do so, and this will result
1105 * in them getting along in perfect harmony.
1107 * If you do have a dedicated thread doing event handling, it is perfectly
1108 * legal for it to take the event handling lock for long periods of time. Any
1109 * synchronous I/O functions you call from other threads will transparently
1110 * fall back to the "event waiters" mechanism detailed above. The only
1111 * consideration that your event handling thread must apply is the one related
1112 * to libusb_event_handling_ok(): you must call this before every poll(), and
1113 * give up the events lock if instructed.
1116 int usbi_io_init(struct libusb_context *ctx)
1120 usbi_mutex_init(&ctx->flying_transfers_lock);
1121 usbi_mutex_init(&ctx->events_lock);
1122 usbi_mutex_init(&ctx->event_waiters_lock);
1123 usbi_cond_init(&ctx->event_waiters_cond);
1124 usbi_mutex_init(&ctx->event_data_lock);
1125 usbi_tls_key_create(&ctx->event_handling_key);
1126 list_init(&ctx->flying_transfers);
1127 list_init(&ctx->event_sources);
1128 list_init(&ctx->removed_event_sources);
1129 list_init(&ctx->hotplug_msgs);
1130 list_init(&ctx->completed_transfers);
1132 r = usbi_create_event(&ctx->event);
1136 r = usbi_add_event_source(ctx, USBI_EVENT_OS_HANDLE(&ctx->event), USBI_EVENT_POLL_EVENTS);
1138 goto err_destroy_event;
1140 #ifdef HAVE_OS_TIMER
1141 r = usbi_create_timer(&ctx->timer);
1143 usbi_dbg("using timer for timeouts");
1144 r = usbi_add_event_source(ctx, USBI_TIMER_OS_HANDLE(&ctx->timer), USBI_TIMER_POLL_EVENTS);
1146 goto err_destroy_timer;
1148 usbi_dbg("timer not available for timeouts");
1154 #ifdef HAVE_OS_TIMER
1156 usbi_destroy_timer(&ctx->timer);
1157 usbi_remove_event_source(ctx, USBI_EVENT_OS_HANDLE(&ctx->event));
1160 usbi_destroy_event(&ctx->event);
1162 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1163 usbi_mutex_destroy(&ctx->events_lock);
1164 usbi_mutex_destroy(&ctx->event_waiters_lock);
1165 usbi_cond_destroy(&ctx->event_waiters_cond);
1166 usbi_mutex_destroy(&ctx->event_data_lock);
1167 usbi_tls_key_delete(ctx->event_handling_key);
1171 static void cleanup_removed_event_sources(struct libusb_context *ctx)
1173 struct usbi_event_source *ievent_source, *tmp;
1175 for_each_removed_event_source_safe(ctx, ievent_source, tmp) {
1176 list_del(&ievent_source->list);
1177 free(ievent_source);
1181 void usbi_io_exit(struct libusb_context *ctx)
1183 #ifdef HAVE_OS_TIMER
1184 if (usbi_using_timer(ctx)) {
1185 usbi_remove_event_source(ctx, USBI_TIMER_OS_HANDLE(&ctx->timer));
1186 usbi_destroy_timer(&ctx->timer);
1189 usbi_remove_event_source(ctx, USBI_EVENT_OS_HANDLE(&ctx->event));
1190 usbi_destroy_event(&ctx->event);
1191 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1192 usbi_mutex_destroy(&ctx->events_lock);
1193 usbi_mutex_destroy(&ctx->event_waiters_lock);
1194 usbi_cond_destroy(&ctx->event_waiters_cond);
1195 usbi_mutex_destroy(&ctx->event_data_lock);
1196 usbi_tls_key_delete(ctx->event_handling_key);
1197 cleanup_removed_event_sources(ctx);
1198 free(ctx->event_data);
1201 static int calculate_timeout(struct usbi_transfer *itransfer)
1204 unsigned int timeout =
1205 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout;
1208 TIMESPEC_CLEAR(&itransfer->timeout);
1212 r = usbi_clock_gettime(USBI_CLOCK_MONOTONIC, &itransfer->timeout);
1214 usbi_err(ITRANSFER_CTX(itransfer),
1215 "failed to read monotonic clock, errno=%d", errno);
1216 return LIBUSB_ERROR_OTHER;
1219 itransfer->timeout.tv_sec += timeout / 1000U;
1220 itransfer->timeout.tv_nsec += (timeout % 1000U) * 1000000L;
1221 if (itransfer->timeout.tv_nsec >= 1000000000L) {
1222 ++itransfer->timeout.tv_sec;
1223 itransfer->timeout.tv_nsec -= 1000000000L;
1229 /** \ingroup libusb_asyncio
1230 * Allocate a libusb transfer with a specified number of isochronous packet
1231 * descriptors. The returned transfer is pre-initialized for you. When the new
1232 * transfer is no longer needed, it should be freed with
1233 * libusb_free_transfer().
1235 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
1236 * interrupt) should specify an iso_packets count of zero.
1238 * For transfers intended for isochronous endpoints, specify an appropriate
1239 * number of packet descriptors to be allocated as part of the transfer.
1240 * The returned transfer is not specially initialized for isochronous I/O;
1241 * you are still required to set the
1242 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
1243 * \ref libusb_transfer::type "type" fields accordingly.
1245 * It is safe to allocate a transfer with some isochronous packets and then
1246 * use it on a non-isochronous endpoint. If you do this, ensure that at time
1247 * of submission, num_iso_packets is 0 and that type is set appropriately.
1249 * \param iso_packets number of isochronous packet descriptors to allocate. Must be non-negative.
1250 * \returns a newly allocated transfer, or NULL on error
1253 struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
1259 struct usbi_transfer *itransfer;
1260 struct libusb_transfer *transfer;
1262 assert(iso_packets >= 0);
1263 if (iso_packets < 0)
1266 priv_size = PTR_ALIGN(usbi_backend.transfer_priv_size);
1267 alloc_size = priv_size
1268 + sizeof(struct usbi_transfer)
1269 + sizeof(struct libusb_transfer)
1270 + (sizeof(struct libusb_iso_packet_descriptor) * (size_t)iso_packets);
1271 ptr = calloc(1, alloc_size);
1275 itransfer = (struct usbi_transfer *)(ptr + priv_size);
1276 itransfer->num_iso_packets = iso_packets;
1277 itransfer->priv = ptr;
1278 usbi_mutex_init(&itransfer->lock);
1279 transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1280 usbi_dbg("transfer %p", transfer);
1284 /** \ingroup libusb_asyncio
1285 * Free a transfer structure. This should be called for all transfers
1286 * allocated with libusb_alloc_transfer().
1288 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
1289 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
1290 * non-NULL, this function will also free the transfer buffer using the
1291 * standard system memory allocator (e.g. free()).
1293 * It is legal to call this function with a NULL transfer. In this case,
1294 * the function will simply return safely.
1296 * It is not legal to free an active transfer (one which has been submitted
1297 * and has not yet completed).
1299 * \param transfer the transfer to free
1301 void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
1303 struct usbi_transfer *itransfer;
1310 usbi_dbg("transfer %p", transfer);
1311 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER)
1312 free(transfer->buffer);
1314 itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1315 usbi_mutex_destroy(&itransfer->lock);
1317 priv_size = PTR_ALIGN(usbi_backend.transfer_priv_size);
1318 ptr = (unsigned char *)itransfer - priv_size;
1319 assert(ptr == itransfer->priv);
1323 /* iterates through the flying transfers, and rearms the timer based on the
1324 * next upcoming timeout.
1325 * must be called with flying_list locked.
1326 * returns 0 on success or a LIBUSB_ERROR code on failure.
1328 #ifdef HAVE_OS_TIMER
1329 static int arm_timer_for_next_timeout(struct libusb_context *ctx)
1331 struct usbi_transfer *itransfer;
1333 if (!usbi_using_timer(ctx))
1336 for_each_transfer(ctx, itransfer) {
1337 struct timespec *cur_ts = &itransfer->timeout;
1339 /* if we've reached transfers of infinite timeout, then we have no
1341 if (!TIMESPEC_IS_SET(cur_ts))
1344 /* act on first transfer that has not already been handled */
1345 if (!(itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))) {
1346 usbi_dbg("next timeout originally %ums", USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout);
1347 return usbi_arm_timer(&ctx->timer, cur_ts);
1351 usbi_dbg("no timeouts, disarming timer");
1352 return usbi_disarm_timer(&ctx->timer);
1355 static inline int arm_timer_for_next_timeout(struct libusb_context *ctx)
1362 /* add a transfer to the (timeout-sorted) active transfers list.
1363 * This function will return non 0 if fails to update the timer,
1364 * in which case the transfer is *not* on the flying_transfers list. */
1365 static int add_to_flying_list(struct usbi_transfer *itransfer)
1367 struct usbi_transfer *cur;
1368 struct timespec *timeout = &itransfer->timeout;
1369 struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
1373 r = calculate_timeout(itransfer);
1377 /* if we have no other flying transfers, start the list with this one */
1378 if (list_empty(&ctx->flying_transfers)) {
1379 list_add(&itransfer->list, &ctx->flying_transfers);
1383 /* if we have infinite timeout, append to end of list */
1384 if (!TIMESPEC_IS_SET(timeout)) {
1385 list_add_tail(&itransfer->list, &ctx->flying_transfers);
1386 /* first is irrelevant in this case */
1390 /* otherwise, find appropriate place in list */
1391 for_each_transfer(ctx, cur) {
1392 /* find first timeout that occurs after the transfer in question */
1393 struct timespec *cur_ts = &cur->timeout;
1395 if (!TIMESPEC_IS_SET(cur_ts) || TIMESPEC_CMP(cur_ts, timeout, >)) {
1396 list_add_tail(&itransfer->list, &cur->list);
1401 /* first is 0 at this stage (list not empty) */
1403 /* otherwise we need to be inserted at the end */
1404 list_add_tail(&itransfer->list, &ctx->flying_transfers);
1406 #ifdef HAVE_OS_TIMER
1407 if (first && usbi_using_timer(ctx) && TIMESPEC_IS_SET(timeout)) {
1408 /* if this transfer has the lowest timeout of all active transfers,
1409 * rearm the timer with this transfer's timeout */
1410 usbi_dbg("arm timer for timeout in %ums (first in line)",
1411 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout);
1412 r = usbi_arm_timer(&ctx->timer, timeout);
1419 list_del(&itransfer->list);
1424 /* remove a transfer from the active transfers list.
1425 * This function will *always* remove the transfer from the
1426 * flying_transfers list. It will return a LIBUSB_ERROR code
1427 * if it fails to update the timer for the next timeout. */
1428 static int remove_from_flying_list(struct usbi_transfer *itransfer)
1430 struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
1434 usbi_mutex_lock(&ctx->flying_transfers_lock);
1435 rearm_timer = (TIMESPEC_IS_SET(&itransfer->timeout) &&
1436 list_first_entry(&ctx->flying_transfers, struct usbi_transfer, list) == itransfer);
1437 list_del(&itransfer->list);
1439 r = arm_timer_for_next_timeout(ctx);
1440 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1445 /** \ingroup libusb_asyncio
1446 * Submit a transfer. This function will fire off the USB transfer and then
1447 * return immediately.
1449 * \param transfer the transfer to submit
1450 * \returns 0 on success
1451 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
1452 * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
1453 * \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
1454 * by the operating system.
1455 * \returns LIBUSB_ERROR_INVALID_PARAM if the transfer size is larger than
1456 * the operating system and/or hardware can support (see \ref asynclimits)
1457 * \returns another LIBUSB_ERROR code on other failure
1459 int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
1461 struct usbi_transfer *itransfer =
1462 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1463 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1466 usbi_dbg("transfer %p", transfer);
1469 * Important note on locking, this function takes / releases locks
1470 * in the following order:
1471 * take flying_transfers_lock
1472 * take itransfer->lock
1474 * add to flying_transfers list
1475 * release flying_transfers_lock
1477 * release itransfer->lock
1479 * take flying_transfers_lock
1480 * remove from flying_transfers list
1481 * release flying_transfers_lock
1483 * Note that it takes locks in the order a-b and then releases them
1484 * in the same order a-b. This is somewhat unusual but not wrong,
1485 * release order is not important as long as *all* locks are released
1486 * before re-acquiring any locks.
1488 * This means that the ordering of first releasing itransfer->lock
1489 * and then re-acquiring the flying_transfers_list on error is
1490 * important and must not be changed!
1492 * This is done this way because when we take both locks we must always
1493 * take flying_transfers_lock first to avoid ab-ba style deadlocks with
1494 * the timeout handling and usbi_handle_disconnect paths.
1496 * And we cannot release itransfer->lock before the submission is
1497 * complete otherwise timeout handling for transfers with short
1498 * timeouts may run before submission.
1500 usbi_mutex_lock(&ctx->flying_transfers_lock);
1501 usbi_mutex_lock(&itransfer->lock);
1502 if (itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT) {
1503 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1504 usbi_mutex_unlock(&itransfer->lock);
1505 return LIBUSB_ERROR_BUSY;
1507 itransfer->transferred = 0;
1508 itransfer->state_flags = 0;
1509 itransfer->timeout_flags = 0;
1510 r = add_to_flying_list(itransfer);
1512 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1513 usbi_mutex_unlock(&itransfer->lock);
1517 * We must release the flying transfers lock here, because with
1518 * some backends the submit_transfer method is synchroneous.
1520 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1522 r = usbi_backend.submit_transfer(itransfer);
1523 if (r == LIBUSB_SUCCESS) {
1524 itransfer->state_flags |= USBI_TRANSFER_IN_FLIGHT;
1525 /* keep a reference to this device */
1526 libusb_ref_device(transfer->dev_handle->dev);
1528 usbi_mutex_unlock(&itransfer->lock);
1530 if (r != LIBUSB_SUCCESS)
1531 remove_from_flying_list(itransfer);
1536 /** \ingroup libusb_asyncio
1537 * Asynchronously cancel a previously submitted transfer.
1538 * This function returns immediately, but this does not indicate cancellation
1539 * is complete. Your callback function will be invoked at some later time
1540 * with a transfer status of
1541 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
1542 * "LIBUSB_TRANSFER_CANCELLED."
1544 * \param transfer the transfer to cancel
1545 * \returns 0 on success
1546 * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is not in progress,
1547 * already complete, or already cancelled.
1548 * \returns a LIBUSB_ERROR code on failure
1550 int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
1552 struct usbi_transfer *itransfer =
1553 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1556 usbi_dbg("transfer %p", transfer );
1557 usbi_mutex_lock(&itransfer->lock);
1558 if (!(itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT)
1559 || (itransfer->state_flags & USBI_TRANSFER_CANCELLING)) {
1560 r = LIBUSB_ERROR_NOT_FOUND;
1563 r = usbi_backend.cancel_transfer(itransfer);
1565 if (r != LIBUSB_ERROR_NOT_FOUND &&
1566 r != LIBUSB_ERROR_NO_DEVICE)
1567 usbi_err(TRANSFER_CTX(transfer),
1568 "cancel transfer failed error %d", r);
1570 usbi_dbg("cancel transfer failed error %d", r);
1572 if (r == LIBUSB_ERROR_NO_DEVICE)
1573 itransfer->state_flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
1576 itransfer->state_flags |= USBI_TRANSFER_CANCELLING;
1579 usbi_mutex_unlock(&itransfer->lock);
1583 /** \ingroup libusb_asyncio
1584 * Set a transfers bulk stream id. Note users are advised to use
1585 * libusb_fill_bulk_stream_transfer() instead of calling this function
1588 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1590 * \param transfer the transfer to set the stream id for
1591 * \param stream_id the stream id to set
1592 * \see libusb_alloc_streams()
1594 void API_EXPORTED libusb_transfer_set_stream_id(
1595 struct libusb_transfer *transfer, uint32_t stream_id)
1597 struct usbi_transfer *itransfer =
1598 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1600 itransfer->stream_id = stream_id;
1603 /** \ingroup libusb_asyncio
1604 * Get a transfers bulk stream id.
1606 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1608 * \param transfer the transfer to get the stream id for
1609 * \returns the stream id for the transfer
1611 uint32_t API_EXPORTED libusb_transfer_get_stream_id(
1612 struct libusb_transfer *transfer)
1614 struct usbi_transfer *itransfer =
1615 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1617 return itransfer->stream_id;
1620 /* Handle completion of a transfer (completion might be an error condition).
1621 * This will invoke the user-supplied callback function, which may end up
1622 * freeing the transfer. Therefore you cannot use the transfer structure
1623 * after calling this function, and you should free all backend-specific
1624 * data before calling it.
1625 * Do not call this function with the usbi_transfer lock held. User-specified
1626 * callback functions may attempt to directly resubmit the transfer, which
1627 * will attempt to take the lock. */
1628 int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1629 enum libusb_transfer_status status)
1631 struct libusb_transfer *transfer =
1632 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1633 struct libusb_device_handle *dev_handle = transfer->dev_handle;
1637 r = remove_from_flying_list(itransfer);
1639 usbi_err(ITRANSFER_CTX(itransfer), "failed to set timer for next timeout");
1641 usbi_mutex_lock(&itransfer->lock);
1642 itransfer->state_flags &= ~USBI_TRANSFER_IN_FLIGHT;
1643 usbi_mutex_unlock(&itransfer->lock);
1645 if (status == LIBUSB_TRANSFER_COMPLETED
1646 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1647 int rqlen = transfer->length;
1648 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1649 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1650 if (rqlen != itransfer->transferred) {
1651 usbi_dbg("interpreting short transfer as error");
1652 status = LIBUSB_TRANSFER_ERROR;
1656 flags = transfer->flags;
1657 transfer->status = status;
1658 transfer->actual_length = itransfer->transferred;
1659 usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
1660 if (transfer->callback)
1661 transfer->callback(transfer);
1662 /* transfer might have been freed by the above call, do not use from
1664 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1665 libusb_free_transfer(transfer);
1666 libusb_unref_device(dev_handle->dev);
1670 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1671 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1672 * transfers exist here.
1673 * Do not call this function with the usbi_transfer lock held. User-specified
1674 * callback functions may attempt to directly resubmit the transfer, which
1675 * will attempt to take the lock. */
1676 int usbi_handle_transfer_cancellation(struct usbi_transfer *itransfer)
1678 struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
1681 usbi_mutex_lock(&ctx->flying_transfers_lock);
1682 timed_out = itransfer->timeout_flags & USBI_TRANSFER_TIMED_OUT;
1683 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1685 /* if the URB was cancelled due to timeout, report timeout to the user */
1687 usbi_dbg("detected timeout cancellation");
1688 return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_TIMED_OUT);
1691 /* otherwise its a normal async cancel */
1692 return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_CANCELLED);
1695 /* Add a completed transfer to the completed_transfers list of the
1696 * context and signal the event. The backend's handle_transfer_completion()
1697 * function will be called the next time an event handler runs. */
1698 void usbi_signal_transfer_completion(struct usbi_transfer *itransfer)
1700 libusb_device_handle *dev_handle = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->dev_handle;
1703 struct libusb_context *ctx = HANDLE_CTX(dev_handle);
1704 unsigned int event_flags;
1706 usbi_mutex_lock(&ctx->event_data_lock);
1707 event_flags = ctx->event_flags;
1708 ctx->event_flags |= USBI_EVENT_TRANSFER_COMPLETED;
1709 list_add_tail(&itransfer->completed_list, &ctx->completed_transfers);
1711 usbi_signal_event(&ctx->event);
1712 usbi_mutex_unlock(&ctx->event_data_lock);
1716 /** \ingroup libusb_poll
1717 * Attempt to acquire the event handling lock. This lock is used to ensure that
1718 * only one thread is monitoring libusb event sources at any one time.
1720 * You only need to use this lock if you are developing an application
1721 * which calls poll() or select() on libusb's file descriptors directly.
1722 * If you stick to libusb's event handling loop functions (e.g.
1723 * libusb_handle_events()) then you do not need to be concerned with this
1726 * While holding this lock, you are trusted to actually be handling events.
1727 * If you are no longer handling events, you must call libusb_unlock_events()
1728 * as soon as possible.
1730 * \param ctx the context to operate on, or NULL for the default context
1731 * \returns 0 if the lock was obtained successfully
1732 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1733 * \ref libusb_mtasync
1735 int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
1740 ctx = usbi_get_context(ctx);
1742 /* is someone else waiting to close a device? if so, don't let this thread
1743 * start event handling */
1744 usbi_mutex_lock(&ctx->event_data_lock);
1745 ru = ctx->device_close;
1746 usbi_mutex_unlock(&ctx->event_data_lock);
1748 usbi_dbg("someone else is closing a device");
1752 r = usbi_mutex_trylock(&ctx->events_lock);
1756 ctx->event_handler_active = 1;
1760 /** \ingroup libusb_poll
1761 * Acquire the event handling lock, blocking until successful acquisition if
1762 * it is contended. This lock is used to ensure that only one thread is
1763 * monitoring libusb event sources at any one time.
1765 * You only need to use this lock if you are developing an application
1766 * which calls poll() or select() on libusb's file descriptors directly.
1767 * If you stick to libusb's event handling loop functions (e.g.
1768 * libusb_handle_events()) then you do not need to be concerned with this
1771 * While holding this lock, you are trusted to actually be handling events.
1772 * If you are no longer handling events, you must call libusb_unlock_events()
1773 * as soon as possible.
1775 * \param ctx the context to operate on, or NULL for the default context
1776 * \ref libusb_mtasync
1778 void API_EXPORTED libusb_lock_events(libusb_context *ctx)
1780 ctx = usbi_get_context(ctx);
1781 usbi_mutex_lock(&ctx->events_lock);
1782 ctx->event_handler_active = 1;
1785 /** \ingroup libusb_poll
1786 * Release the lock previously acquired with libusb_try_lock_events() or
1787 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1788 * on libusb_wait_for_event().
1790 * \param ctx the context to operate on, or NULL for the default context
1791 * \ref libusb_mtasync
1793 void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
1795 ctx = usbi_get_context(ctx);
1796 ctx->event_handler_active = 0;
1797 usbi_mutex_unlock(&ctx->events_lock);
1799 /* FIXME: perhaps we should be a bit more efficient by not broadcasting
1800 * the availability of the events lock when we are modifying pollfds
1801 * (check ctx->device_close)? */
1802 usbi_mutex_lock(&ctx->event_waiters_lock);
1803 usbi_cond_broadcast(&ctx->event_waiters_cond);
1804 usbi_mutex_unlock(&ctx->event_waiters_lock);
1807 /** \ingroup libusb_poll
1808 * Determine if it is still OK for this thread to be doing event handling.
1810 * Sometimes, libusb needs to temporarily pause all event handlers, and this
1811 * is the function you should use before polling file descriptors to see if
1814 * If this function instructs your thread to give up the events lock, you
1815 * should just continue the usual logic that is documented in \ref libusb_mtasync.
1816 * On the next iteration, your thread will fail to obtain the events lock,
1817 * and will hence become an event waiter.
1819 * This function should be called while the events lock is held: you don't
1820 * need to worry about the results of this function if your thread is not
1821 * the current event handler.
1823 * \param ctx the context to operate on, or NULL for the default context
1824 * \returns 1 if event handling can start or continue
1825 * \returns 0 if this thread must give up the events lock
1826 * \ref fullstory "Multi-threaded I/O: the full story"
1828 int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
1832 ctx = usbi_get_context(ctx);
1834 /* is someone else waiting to close a device? if so, don't let this thread
1835 * continue event handling */
1836 usbi_mutex_lock(&ctx->event_data_lock);
1837 r = ctx->device_close;
1838 usbi_mutex_unlock(&ctx->event_data_lock);
1840 usbi_dbg("someone else is closing a device");
1848 /** \ingroup libusb_poll
1849 * Determine if an active thread is handling events (i.e. if anyone is holding
1850 * the event handling lock).
1852 * \param ctx the context to operate on, or NULL for the default context
1853 * \returns 1 if a thread is handling events
1854 * \returns 0 if there are no threads currently handling events
1855 * \ref libusb_mtasync
1857 int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
1861 ctx = usbi_get_context(ctx);
1863 /* is someone else waiting to close a device? if so, don't let this thread
1864 * start event handling -- indicate that event handling is happening */
1865 usbi_mutex_lock(&ctx->event_data_lock);
1866 r = ctx->device_close;
1867 usbi_mutex_unlock(&ctx->event_data_lock);
1869 usbi_dbg("someone else is closing a device");
1873 return ctx->event_handler_active;
1876 /** \ingroup libusb_poll
1877 * Interrupt any active thread that is handling events. This is mainly useful
1878 * for interrupting a dedicated event handling thread when an application
1879 * wishes to call libusb_exit().
1881 * Since version 1.0.21, \ref LIBUSB_API_VERSION >= 0x01000105
1883 * \param ctx the context to operate on, or NULL for the default context
1884 * \ref libusb_mtasync
1886 void API_EXPORTED libusb_interrupt_event_handler(libusb_context *ctx)
1888 unsigned int event_flags;
1892 ctx = usbi_get_context(ctx);
1893 usbi_mutex_lock(&ctx->event_data_lock);
1895 event_flags = ctx->event_flags;
1896 ctx->event_flags |= USBI_EVENT_USER_INTERRUPT;
1898 usbi_signal_event(&ctx->event);
1900 usbi_mutex_unlock(&ctx->event_data_lock);
1903 /** \ingroup libusb_poll
1904 * Acquire the event waiters lock. This lock is designed to be obtained under
1905 * the situation where you want to be aware when events are completed, but
1906 * some other thread is event handling so calling libusb_handle_events() is not
1909 * You then obtain this lock, re-check that another thread is still handling
1910 * events, then call libusb_wait_for_event().
1912 * You only need to use this lock if you are developing an application
1913 * which calls poll() or select() on libusb's file descriptors directly,
1914 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1915 * If you stick to libusb's event handling loop functions (e.g.
1916 * libusb_handle_events()) then you do not need to be concerned with this
1919 * \param ctx the context to operate on, or NULL for the default context
1920 * \ref libusb_mtasync
1922 void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
1924 ctx = usbi_get_context(ctx);
1925 usbi_mutex_lock(&ctx->event_waiters_lock);
1928 /** \ingroup libusb_poll
1929 * Release the event waiters lock.
1930 * \param ctx the context to operate on, or NULL for the default context
1931 * \ref libusb_mtasync
1933 void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
1935 ctx = usbi_get_context(ctx);
1936 usbi_mutex_unlock(&ctx->event_waiters_lock);
1939 /** \ingroup libusb_poll
1940 * Wait for another thread to signal completion of an event. Must be called
1941 * with the event waiters lock held, see libusb_lock_event_waiters().
1943 * This function will block until any of the following conditions are met:
1944 * -# The timeout expires
1945 * -# A transfer completes
1946 * -# A thread releases the event handling lock through libusb_unlock_events()
1948 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1949 * the callback for the transfer has completed. Condition 3 is important
1950 * because it means that the thread that was previously handling events is no
1951 * longer doing so, so if any events are to complete, another thread needs to
1952 * step up and start event handling.
1954 * This function releases the event waiters lock before putting your thread
1955 * to sleep, and reacquires the lock as it is being woken up.
1957 * \param ctx the context to operate on, or NULL for the default context
1958 * \param tv maximum timeout for this blocking function. A NULL value
1959 * indicates unlimited timeout.
1960 * \returns 0 after a transfer completes or another thread stops event handling
1961 * \returns 1 if the timeout expired
1962 * \ref libusb_mtasync
1964 int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
1968 ctx = usbi_get_context(ctx);
1970 usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
1974 r = usbi_cond_timedwait(&ctx->event_waiters_cond,
1975 &ctx->event_waiters_lock, tv);
1980 return (r == ETIMEDOUT);
1983 static void handle_timeout(struct usbi_transfer *itransfer)
1985 struct libusb_transfer *transfer =
1986 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1989 itransfer->timeout_flags |= USBI_TRANSFER_TIMEOUT_HANDLED;
1990 r = libusb_cancel_transfer(transfer);
1991 if (r == LIBUSB_SUCCESS)
1992 itransfer->timeout_flags |= USBI_TRANSFER_TIMED_OUT;
1994 usbi_warn(TRANSFER_CTX(transfer),
1995 "async cancel failed %d errno=%d", r, errno);
1998 static int handle_timeouts_locked(struct libusb_context *ctx)
2001 struct timespec systime;
2002 struct usbi_transfer *itransfer;
2004 if (list_empty(&ctx->flying_transfers))
2007 /* get current time */
2008 r = usbi_clock_gettime(USBI_CLOCK_MONOTONIC, &systime);
2010 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2011 return LIBUSB_ERROR_OTHER;
2014 /* iterate through flying transfers list, finding all transfers that
2015 * have expired timeouts */
2016 for_each_transfer(ctx, itransfer) {
2017 struct timespec *cur_ts = &itransfer->timeout;
2019 /* if we've reached transfers of infinite timeout, we're all done */
2020 if (!TIMESPEC_IS_SET(cur_ts))
2023 /* ignore timeouts we've already handled */
2024 if (itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2027 /* if transfer has non-expired timeout, nothing more to do */
2028 if (TIMESPEC_CMP(cur_ts, &systime, >))
2031 /* otherwise, we've got an expired timeout to handle */
2032 handle_timeout(itransfer);
2037 static int handle_timeouts(struct libusb_context *ctx)
2041 ctx = usbi_get_context(ctx);
2042 usbi_mutex_lock(&ctx->flying_transfers_lock);
2043 r = handle_timeouts_locked(ctx);
2044 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2048 static int handle_event_trigger(struct libusb_context *ctx)
2050 struct list_head hotplug_msgs;
2053 usbi_dbg("event triggered");
2055 list_init(&hotplug_msgs);
2057 /* take the the event data lock while processing events */
2058 usbi_mutex_lock(&ctx->event_data_lock);
2060 /* check if someone modified the event sources */
2061 if (ctx->event_flags & USBI_EVENT_EVENT_SOURCES_MODIFIED)
2062 usbi_dbg("someone updated the event sources");
2064 if (ctx->event_flags & USBI_EVENT_USER_INTERRUPT) {
2065 usbi_dbg("someone purposefully interrupted");
2066 ctx->event_flags &= ~USBI_EVENT_USER_INTERRUPT;
2069 /* check if someone is closing a device */
2070 if (ctx->event_flags & USBI_EVENT_DEVICE_CLOSE)
2071 usbi_dbg("someone is closing a device");
2073 /* check for any pending hotplug messages */
2074 if (ctx->event_flags & USBI_EVENT_HOTPLUG_MSG_PENDING) {
2075 usbi_dbg("hotplug message received");
2076 ctx->event_flags &= ~USBI_EVENT_HOTPLUG_MSG_PENDING;
2077 assert(!list_empty(&ctx->hotplug_msgs));
2078 list_cut(&hotplug_msgs, &ctx->hotplug_msgs);
2081 /* complete any pending transfers */
2082 if (ctx->event_flags & USBI_EVENT_TRANSFER_COMPLETED) {
2083 assert(!list_empty(&ctx->completed_transfers));
2084 while (r == 0 && !list_empty(&ctx->completed_transfers)) {
2085 struct usbi_transfer *itransfer =
2086 list_first_entry(&ctx->completed_transfers, struct usbi_transfer, completed_list);
2088 list_del(&itransfer->completed_list);
2089 usbi_mutex_unlock(&ctx->event_data_lock);
2090 r = usbi_backend.handle_transfer_completion(itransfer);
2092 usbi_err(ctx, "backend handle_transfer_completion failed with error %d", r);
2093 usbi_mutex_lock(&ctx->event_data_lock);
2096 if (list_empty(&ctx->completed_transfers))
2097 ctx->event_flags &= ~USBI_EVENT_TRANSFER_COMPLETED;
2100 /* if no further pending events, clear the event */
2101 if (!ctx->event_flags)
2102 usbi_clear_event(&ctx->event);
2104 usbi_mutex_unlock(&ctx->event_data_lock);
2106 /* process the hotplug messages, if any */
2107 while (!list_empty(&hotplug_msgs)) {
2108 struct libusb_hotplug_message *message =
2109 list_first_entry(&hotplug_msgs, struct libusb_hotplug_message, list);
2111 usbi_hotplug_match(ctx, message->device, message->event);
2113 /* the device left, dereference the device */
2114 if (message->event == LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT)
2115 libusb_unref_device(message->device);
2117 list_del(&message->list);
2124 #ifdef HAVE_OS_TIMER
2125 static int handle_timer_trigger(struct libusb_context *ctx)
2129 usbi_mutex_lock(&ctx->flying_transfers_lock);
2131 /* process the timeout that just happened */
2132 r = handle_timeouts_locked(ctx);
2136 /* arm for next timeout */
2137 r = arm_timer_for_next_timeout(ctx);
2140 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2145 /* do the actual event handling. assumes that no other thread is concurrently
2146 * doing the same thing. */
2147 static int handle_events(struct libusb_context *ctx, struct timeval *tv)
2149 struct usbi_reported_events reported_events;
2152 /* prevent attempts to recursively handle events (e.g. calling into
2153 * libusb_handle_events() from within a hotplug or transfer callback) */
2154 if (usbi_handling_events(ctx))
2155 return LIBUSB_ERROR_BUSY;
2157 /* only reallocate the event source data when the list of event sources has
2158 * been modified since the last handle_events(), otherwise reuse them to
2159 * save the additional overhead */
2160 usbi_mutex_lock(&ctx->event_data_lock);
2161 if (ctx->event_flags & USBI_EVENT_EVENT_SOURCES_MODIFIED) {
2162 usbi_dbg("event sources modified, reallocating event data");
2164 /* free anything removed since we last ran */
2165 cleanup_removed_event_sources(ctx);
2167 r = usbi_alloc_event_data(ctx);
2169 usbi_mutex_unlock(&ctx->event_data_lock);
2173 /* reset the flag now that we have the updated list */
2174 ctx->event_flags &= ~USBI_EVENT_EVENT_SOURCES_MODIFIED;
2176 /* if no further pending events, clear the event so that we do
2177 * not immediately return from the wait function */
2178 if (!ctx->event_flags)
2179 usbi_clear_event(&ctx->event);
2181 usbi_mutex_unlock(&ctx->event_data_lock);
2183 timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000);
2185 /* round up to next millisecond */
2186 if (tv->tv_usec % 1000)
2189 usbi_start_event_handling(ctx);
2191 r = usbi_wait_for_events(ctx, &reported_events, timeout_ms);
2192 if (r != LIBUSB_SUCCESS) {
2193 if (r == LIBUSB_ERROR_TIMEOUT)
2194 r = handle_timeouts(ctx);
2198 if (reported_events.event_triggered) {
2199 r = handle_event_trigger(ctx);
2201 /* return error code */
2206 #ifdef HAVE_OS_TIMER
2207 if (reported_events.timer_triggered) {
2208 r = handle_timer_trigger(ctx);
2210 /* return error code */
2216 if (!reported_events.num_ready)
2219 r = usbi_backend.handle_events(ctx, reported_events.event_data,
2220 reported_events.event_data_count, reported_events.num_ready);
2222 usbi_err(ctx, "backend handle_events failed with error %d", r);
2225 usbi_end_event_handling(ctx);
2229 /* returns the smallest of:
2230 * 1. timeout of next URB
2231 * 2. user-supplied timeout
2232 * returns 1 if there is an already-expired timeout, otherwise returns 0
2235 static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
2236 struct timeval *out)
2238 struct timeval timeout;
2239 int r = libusb_get_next_timeout(ctx, &timeout);
2241 /* timeout already expired? */
2242 if (!timerisset(&timeout))
2245 /* choose the smallest of next URB timeout or user specified timeout */
2246 if (timercmp(&timeout, tv, <))
2256 /** \ingroup libusb_poll
2257 * Handle any pending events.
2259 * libusb determines "pending events" by checking if any timeouts have expired
2260 * and by checking the set of file descriptors for activity.
2262 * If a zero timeval is passed, this function will handle any already-pending
2263 * events and then immediately return in non-blocking style.
2265 * If a non-zero timeval is passed and no events are currently pending, this
2266 * function will block waiting for events to handle up until the specified
2267 * timeout. If an event arrives or a signal is raised, this function will
2270 * If the parameter completed is not NULL then <em>after obtaining the event
2271 * handling lock</em> this function will return immediately if the integer
2272 * pointed to is not 0. This allows for race free waiting for the completion
2273 * of a specific transfer.
2275 * \param ctx the context to operate on, or NULL for the default context
2276 * \param tv the maximum time to block waiting for events, or an all zero
2277 * timeval struct for non-blocking mode
2278 * \param completed pointer to completion integer to check, or NULL
2279 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2280 * \ref libusb_mtasync
2282 int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
2283 struct timeval *tv, int *completed)
2286 struct timeval poll_timeout;
2288 ctx = usbi_get_context(ctx);
2289 r = get_next_timeout(ctx, tv, &poll_timeout);
2291 /* timeout already expired */
2292 return handle_timeouts(ctx);
2296 if (libusb_try_lock_events(ctx) == 0) {
2297 if (completed == NULL || !*completed) {
2298 /* we obtained the event lock: do our own event handling */
2299 usbi_dbg("doing our own event handling");
2300 r = handle_events(ctx, &poll_timeout);
2302 libusb_unlock_events(ctx);
2306 /* another thread is doing event handling. wait for thread events that
2307 * notify event completion. */
2308 libusb_lock_event_waiters(ctx);
2310 if (completed && *completed)
2313 if (!libusb_event_handler_active(ctx)) {
2314 /* we hit a race: whoever was event handling earlier finished in the
2315 * time it took us to reach this point. try the cycle again. */
2316 libusb_unlock_event_waiters(ctx);
2317 usbi_dbg("event handler was active but went away, retrying");
2321 usbi_dbg("another thread is doing event handling");
2322 r = libusb_wait_for_event(ctx, &poll_timeout);
2325 libusb_unlock_event_waiters(ctx);
2330 return handle_timeouts(ctx);
2335 /** \ingroup libusb_poll
2336 * Handle any pending events
2338 * Like libusb_handle_events_timeout_completed(), but without the completed
2339 * parameter, calling this function is equivalent to calling
2340 * libusb_handle_events_timeout_completed() with a NULL completed parameter.
2342 * This function is kept primarily for backwards compatibility.
2343 * All new code should call libusb_handle_events_completed() or
2344 * libusb_handle_events_timeout_completed() to avoid race conditions.
2346 * \param ctx the context to operate on, or NULL for the default context
2347 * \param tv the maximum time to block waiting for events, or an all zero
2348 * timeval struct for non-blocking mode
2349 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2351 int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
2354 return libusb_handle_events_timeout_completed(ctx, tv, NULL);
2357 /** \ingroup libusb_poll
2358 * Handle any pending events in blocking mode. There is currently a timeout
2359 * hardcoded at 60 seconds but we plan to make it unlimited in future. For
2360 * finer control over whether this function is blocking or non-blocking, or
2361 * for control over the timeout, use libusb_handle_events_timeout_completed()
2364 * This function is kept primarily for backwards compatibility.
2365 * All new code should call libusb_handle_events_completed() or
2366 * libusb_handle_events_timeout_completed() to avoid race conditions.
2368 * \param ctx the context to operate on, or NULL for the default context
2369 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2371 int API_EXPORTED libusb_handle_events(libusb_context *ctx)
2376 return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
2379 /** \ingroup libusb_poll
2380 * Handle any pending events in blocking mode.
2382 * Like libusb_handle_events(), with the addition of a completed parameter
2383 * to allow for race free waiting for the completion of a specific transfer.
2385 * See libusb_handle_events_timeout_completed() for details on the completed
2388 * \param ctx the context to operate on, or NULL for the default context
2389 * \param completed pointer to completion integer to check, or NULL
2390 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2391 * \ref libusb_mtasync
2393 int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
2399 return libusb_handle_events_timeout_completed(ctx, &tv, completed);
2402 /** \ingroup libusb_poll
2403 * Handle any pending events by polling file descriptors, without checking if
2404 * any other threads are already doing so. Must be called with the event lock
2405 * held, see libusb_lock_events().
2407 * This function is designed to be called under the situation where you have
2408 * taken the event lock and are calling poll()/select() directly on libusb's
2409 * file descriptors (as opposed to using libusb_handle_events() or similar).
2410 * You detect events on libusb's descriptors, so you then call this function
2411 * with a zero timeout value (while still holding the event lock).
2413 * \param ctx the context to operate on, or NULL for the default context
2414 * \param tv the maximum time to block waiting for events, or zero for
2416 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2417 * \ref libusb_mtasync
2419 int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
2423 struct timeval poll_timeout;
2425 ctx = usbi_get_context(ctx);
2426 r = get_next_timeout(ctx, tv, &poll_timeout);
2428 /* timeout already expired */
2429 return handle_timeouts(ctx);
2432 return handle_events(ctx, &poll_timeout);
2435 /** \ingroup libusb_poll
2436 * Determines whether your application must apply special timing considerations
2437 * when monitoring libusb's file descriptors.
2439 * This function is only useful for applications which retrieve and poll
2440 * libusb's file descriptors in their own main loop (\ref libusb_pollmain).
2442 * Ordinarily, libusb's event handler needs to be called into at specific
2443 * moments in time (in addition to times when there is activity on the file
2444 * descriptor set). The usual approach is to use libusb_get_next_timeout()
2445 * to learn about when the next timeout occurs, and to adjust your
2446 * poll()/select() timeout accordingly so that you can make a call into the
2447 * library at that time.
2449 * Some platforms supported by libusb do not come with this baggage - any
2450 * events relevant to timing will be represented by activity on the file
2451 * descriptor set, and libusb_get_next_timeout() will always return 0.
2452 * This function allows you to detect whether you are running on such a
2457 * \param ctx the context to operate on, or NULL for the default context
2458 * \returns 0 if you must call into libusb at times determined by
2459 * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
2460 * or through regular activity on the file descriptors.
2461 * \ref libusb_pollmain "Polling libusb file descriptors for event handling"
2463 int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
2465 ctx = usbi_get_context(ctx);
2466 return usbi_using_timer(ctx);
2469 /** \ingroup libusb_poll
2470 * Determine the next internal timeout that libusb needs to handle. You only
2471 * need to use this function if you are calling poll() or select() or similar
2472 * on libusb's file descriptors yourself - you do not need to use it if you
2473 * are calling libusb_handle_events() or a variant directly.
2475 * You should call this function in your main loop in order to determine how
2476 * long to wait for select() or poll() to return results. libusb needs to be
2477 * called into at this timeout, so you should use it as an upper bound on
2478 * your select() or poll() call.
2480 * When the timeout has expired, call into libusb_handle_events_timeout()
2481 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
2483 * This function may return 1 (success) and an all-zero timeval. If this is
2484 * the case, it indicates that libusb has a timeout that has already expired
2485 * so you should call libusb_handle_events_timeout() or similar immediately.
2486 * A return code of 0 indicates that there are no pending timeouts.
2488 * On some platforms, this function will always returns 0 (no pending
2489 * timeouts). See \ref polltime.
2491 * \param ctx the context to operate on, or NULL for the default context
2492 * \param tv output location for a relative time against the current
2493 * clock in which libusb must be called into in order to process timeout events
2494 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
2495 * or LIBUSB_ERROR_OTHER on failure
2497 int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
2500 struct usbi_transfer *itransfer;
2501 struct timespec systime;
2502 struct timespec next_timeout = { 0, 0 };
2505 ctx = usbi_get_context(ctx);
2506 if (usbi_using_timer(ctx))
2509 usbi_mutex_lock(&ctx->flying_transfers_lock);
2510 if (list_empty(&ctx->flying_transfers)) {
2511 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2512 usbi_dbg("no URBs, no timeout!");
2516 /* find next transfer which hasn't already been processed as timed out */
2517 for_each_transfer(ctx, itransfer) {
2518 if (itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2521 /* if we've reached transfers of infinte timeout, we're done looking */
2522 if (!TIMESPEC_IS_SET(&itransfer->timeout))
2525 next_timeout = itransfer->timeout;
2528 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2530 if (!TIMESPEC_IS_SET(&next_timeout)) {
2531 usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
2535 r = usbi_clock_gettime(USBI_CLOCK_MONOTONIC, &systime);
2537 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2541 if (!TIMESPEC_CMP(&systime, &next_timeout, <)) {
2542 usbi_dbg("first timeout already expired");
2545 TIMESPEC_SUB(&next_timeout, &systime, &next_timeout);
2546 TIMESPEC_TO_TIMEVAL(tv, &next_timeout);
2547 usbi_dbg("next timeout in %ld.%06lds", (long)tv->tv_sec, (long)tv->tv_usec);
2553 /** \ingroup libusb_poll
2554 * Register notification functions for file descriptor additions/removals.
2555 * These functions will be invoked for every new or removed file descriptor
2556 * that libusb uses as an event source.
2558 * To remove notifiers, pass NULL values for the function pointers.
2560 * Note that file descriptors may have been added even before you register
2561 * these notifiers (e.g. at libusb_init() time).
2563 * Additionally, note that the removal notifier may be called during
2564 * libusb_exit() (e.g. when it is closing file descriptors that were opened
2565 * and added to the poll set at libusb_init() time). If you don't want this,
2566 * remove the notifiers immediately before calling libusb_exit().
2568 * \param ctx the context to operate on, or NULL for the default context
2569 * \param added_cb pointer to function for addition notifications
2570 * \param removed_cb pointer to function for removal notifications
2571 * \param user_data User data to be passed back to callbacks (useful for
2572 * passing context information)
2574 void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
2575 libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
2578 #if !defined(_WIN32) && !defined(__CYGWIN__)
2579 ctx = usbi_get_context(ctx);
2580 ctx->fd_added_cb = added_cb;
2581 ctx->fd_removed_cb = removed_cb;
2582 ctx->fd_cb_user_data = user_data;
2584 usbi_err(ctx, "external polling of libusb's internal event sources " \
2585 "is not yet supported on Windows");
2593 * Interrupt the iteration of the event handling thread, so that it picks
2594 * up the event source change. Callers of this function must hold the event_data_lock.
2596 static void usbi_event_source_notification(struct libusb_context *ctx)
2598 unsigned int event_flags;
2600 /* Record that there is a new poll fd.
2601 * Only signal an event if there are no prior pending events. */
2602 event_flags = ctx->event_flags;
2603 ctx->event_flags |= USBI_EVENT_EVENT_SOURCES_MODIFIED;
2605 usbi_signal_event(&ctx->event);
2608 /* Add an event source to the list of event sources to be monitored.
2609 * poll_events should be specified as a bitmask of events passed to poll(), e.g.
2610 * POLLIN and/or POLLOUT. */
2611 int usbi_add_event_source(struct libusb_context *ctx, usbi_os_handle_t os_handle, short poll_events)
2613 struct usbi_event_source *ievent_source = malloc(sizeof(*ievent_source));
2616 return LIBUSB_ERROR_NO_MEM;
2618 usbi_dbg("add " USBI_OS_HANDLE_FORMAT_STRING " events %d", os_handle, poll_events);
2619 ievent_source->data.os_handle = os_handle;
2620 ievent_source->data.poll_events = poll_events;
2621 usbi_mutex_lock(&ctx->event_data_lock);
2622 list_add_tail(&ievent_source->list, &ctx->event_sources);
2623 usbi_event_source_notification(ctx);
2624 usbi_mutex_unlock(&ctx->event_data_lock);
2626 #if !defined(_WIN32) && !defined(__CYGWIN__)
2627 if (ctx->fd_added_cb)
2628 ctx->fd_added_cb(os_handle, poll_events, ctx->fd_cb_user_data);
2634 /* Remove an event source from the list of event sources to be monitored. */
2635 void usbi_remove_event_source(struct libusb_context *ctx, usbi_os_handle_t os_handle)
2637 struct usbi_event_source *ievent_source;
2640 usbi_dbg("remove " USBI_OS_HANDLE_FORMAT_STRING, os_handle);
2641 usbi_mutex_lock(&ctx->event_data_lock);
2642 for_each_event_source(ctx, ievent_source) {
2643 if (ievent_source->data.os_handle == os_handle) {
2650 usbi_dbg("couldn't find " USBI_OS_HANDLE_FORMAT_STRING " to remove", os_handle);
2651 usbi_mutex_unlock(&ctx->event_data_lock);
2655 list_del(&ievent_source->list);
2656 list_add_tail(&ievent_source->list, &ctx->removed_event_sources);
2657 usbi_event_source_notification(ctx);
2658 usbi_mutex_unlock(&ctx->event_data_lock);
2660 #if !defined(_WIN32) && !defined(__CYGWIN__)
2661 if (ctx->fd_removed_cb)
2662 ctx->fd_removed_cb(os_handle, ctx->fd_cb_user_data);
2666 /** \ingroup libusb_poll
2667 * Retrieve a list of file descriptors that should be polled by your main loop
2668 * as libusb event sources.
2670 * The returned list is NULL-terminated and should be freed with libusb_free_pollfds()
2671 * when done. The actual list contents must not be touched.
2673 * As file descriptors are a Unix-specific concept, this function is not
2674 * available on Windows and will always return NULL.
2676 * \param ctx the context to operate on, or NULL for the default context
2677 * \returns a NULL-terminated list of libusb_pollfd structures
2678 * \returns NULL on error
2679 * \returns NULL on platforms where the functionality is not available
2682 const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
2683 libusb_context *ctx)
2685 #if !defined(_WIN32) && !defined(__CYGWIN__)
2686 struct libusb_pollfd **ret = NULL;
2687 struct usbi_event_source *ievent_source;
2690 static_assert(sizeof(struct usbi_event_source_data) == sizeof(struct libusb_pollfd),
2691 "mismatch between usbi_event_source_data and libusb_pollfd sizes");
2693 ctx = usbi_get_context(ctx);
2695 usbi_mutex_lock(&ctx->event_data_lock);
2698 for_each_event_source(ctx, ievent_source)
2701 ret = calloc(i + 1, sizeof(struct libusb_pollfd *));
2706 for_each_event_source(ctx, ievent_source)
2707 ret[i++] = (struct libusb_pollfd *)ievent_source;
2710 usbi_mutex_unlock(&ctx->event_data_lock);
2711 return (const struct libusb_pollfd **)ret;
2713 usbi_err(ctx, "external polling of libusb's internal event sources " \
2714 "is not yet supported on Windows");
2719 /** \ingroup libusb_poll
2720 * Free a list of libusb_pollfd structures. This should be called for all
2721 * pollfd lists allocated with libusb_get_pollfds().
2723 * Since version 1.0.20, \ref LIBUSB_API_VERSION >= 0x01000104
2725 * It is legal to call this function with a NULL pollfd list. In this case,
2726 * the function will simply do nothing.
2728 * \param pollfds the list of libusb_pollfd structures to free
2730 void API_EXPORTED libusb_free_pollfds(const struct libusb_pollfd **pollfds)
2732 #if !defined(_WIN32) && !defined(__CYGWIN__)
2733 free((void *)pollfds);
2739 /* Backends may call this from handle_events to report disconnection of a
2740 * device. This function ensures transfers get cancelled appropriately.
2741 * Callers of this function must hold the events_lock.
2743 void usbi_handle_disconnect(struct libusb_device_handle *dev_handle)
2745 struct libusb_context *ctx = HANDLE_CTX(dev_handle);
2746 struct usbi_transfer *cur;
2747 struct usbi_transfer *to_cancel;
2749 usbi_dbg("device %d.%d",
2750 dev_handle->dev->bus_number, dev_handle->dev->device_address);
2752 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
2755 * when we find a transfer for this device on the list, there are two
2756 * possible scenarios:
2757 * 1. the transfer is currently in-flight, in which case we terminate the
2759 * 2. the transfer has been added to the flying transfer list by
2760 * libusb_submit_transfer, has failed to submit and
2761 * libusb_submit_transfer is waiting for us to release the
2762 * flying_transfers_lock to remove it, so we ignore it
2767 usbi_mutex_lock(&ctx->flying_transfers_lock);
2768 for_each_transfer(ctx, cur) {
2769 if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == dev_handle) {
2770 usbi_mutex_lock(&cur->lock);
2771 if (cur->state_flags & USBI_TRANSFER_IN_FLIGHT)
2773 usbi_mutex_unlock(&cur->lock);
2779 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2784 usbi_dbg("cancelling transfer %p from disconnect",
2785 USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel));
2787 usbi_mutex_lock(&to_cancel->lock);
2788 usbi_backend.clear_transfer_priv(to_cancel);
2789 usbi_mutex_unlock(&to_cancel->lock);
2790 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);