1 /* -*- Mode: C; indent-tabs-mode:t ; c-basic-offset:8 -*- */
3 * I/O functions for libusb
4 * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
5 * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23 #include <assert.h> // XXX add assert for debugging
32 #ifdef HAVE_SYS_TIME_H
35 #ifdef USBI_TIMERFD_AVAILABLE
36 #include <sys/timerfd.h>
43 * \page io Synchronous and asynchronous device I/O
45 * \section intro Introduction
47 * If you're using libusb in your application, you're probably wanting to
48 * perform I/O with devices - you want to perform USB data transfers.
50 * libusb offers two separate interfaces for device I/O. This page aims to
51 * introduce the two in order to help you decide which one is more suitable
52 * for your application. You can also choose to use both interfaces in your
53 * application by considering each transfer on a case-by-case basis.
55 * Once you have read through the following discussion, you should consult the
56 * detailed API documentation pages for the details:
60 * \section theory Transfers at a logical level
62 * At a logical level, USB transfers typically happen in two parts. For
63 * example, when reading data from a endpoint:
64 * -# A request for data is sent to the device
65 * -# Some time later, the incoming data is received by the host
67 * or when writing data to an endpoint:
69 * -# The data is sent to the device
70 * -# Some time later, the host receives acknowledgement from the device that
71 * the data has been transferred.
73 * There may be an indefinite delay between the two steps. Consider a
74 * fictional USB input device with a button that the user can press. In order
75 * to determine when the button is pressed, you would likely submit a request
76 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
77 * Data will arrive when the button is pressed by the user, which is
78 * potentially hours later.
80 * libusb offers both a synchronous and an asynchronous interface to performing
81 * USB transfers. The main difference is that the synchronous interface
82 * combines both steps indicated above into a single function call, whereas
83 * the asynchronous interface separates them.
85 * \section sync The synchronous interface
87 * The synchronous I/O interface allows you to perform a USB transfer with
88 * a single function call. When the function call returns, the transfer has
89 * completed and you can parse the results.
91 * If you have used the libusb-0.1 before, this I/O style will seem familar to
92 * you. libusb-0.1 only offered a synchronous interface.
94 * In our input device example, to read button presses you might write code
95 * in the following style:
97 unsigned char data[4];
99 int r = libusb_bulk_transfer(handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
100 if (r == 0 && actual_length == sizeof(data)) {
101 // results of the transaction can now be found in the data buffer
102 // parse them here and report button press
108 * The main advantage of this model is simplicity: you did everything with
109 * a single simple function call.
111 * However, this interface has its limitations. Your application will sleep
112 * inside libusb_bulk_transfer() until the transaction has completed. If it
113 * takes the user 3 hours to press the button, your application will be
114 * sleeping for that long. Execution will be tied up inside the library -
115 * the entire thread will be useless for that duration.
117 * Another issue is that by tieing up the thread with that single transaction
118 * there is no possibility of performing I/O with multiple endpoints and/or
119 * multiple devices simultaneously, unless you resort to creating one thread
122 * Additionally, there is no opportunity to cancel the transfer after the
123 * request has been submitted.
125 * For details on how to use the synchronous API, see the
126 * \ref syncio "synchronous I/O API documentation" pages.
128 * \section async The asynchronous interface
130 * Asynchronous I/O is the most significant new feature in libusb-1.0.
131 * Although it is a more complex interface, it solves all the issues detailed
134 * Instead of providing which functions that block until the I/O has complete,
135 * libusb's asynchronous interface presents non-blocking functions which
136 * begin a transfer and then return immediately. Your application passes a
137 * callback function pointer to this non-blocking function, which libusb will
138 * call with the results of the transaction when it has completed.
140 * Transfers which have been submitted through the non-blocking functions
141 * can be cancelled with a separate function call.
143 * The non-blocking nature of this interface allows you to be simultaneously
144 * performing I/O to multiple endpoints on multiple devices, without having
147 * This added flexibility does come with some complications though:
148 * - In the interest of being a lightweight library, libusb does not create
149 * threads and can only operate when your application is calling into it. Your
150 * application must call into libusb from it's main loop when events are ready
151 * to be handled, or you must use some other scheme to allow libusb to
152 * undertake whatever work needs to be done.
153 * - libusb also needs to be called into at certain fixed points in time in
154 * order to accurately handle transfer timeouts.
155 * - Memory handling becomes more complex. You cannot use stack memory unless
156 * the function with that stack is guaranteed not to return until the transfer
157 * callback has finished executing.
158 * - You generally lose some linearity from your code flow because submitting
159 * the transfer request is done in a separate function from where the transfer
160 * results are handled. This becomes particularly obvious when you want to
161 * submit a second transfer based on the results of an earlier transfer.
163 * Internally, libusb's synchronous interface is expressed in terms of function
164 * calls to the asynchronous interface.
166 * For details on how to use the asynchronous API, see the
167 * \ref asyncio "asynchronous I/O API" documentation pages.
172 * \page packetoverflow Packets and overflows
174 * \section packets Packet abstraction
176 * The USB specifications describe how data is transmitted in packets, with
177 * constraints on packet size defined by endpoint descriptors. The host must
178 * not send data payloads larger than the endpoint's maximum packet size.
180 * libusb and the underlying OS abstract out the packet concept, allowing you
181 * to request transfers of any size. Internally, the request will be divided
182 * up into correctly-sized packets. You do not have to be concerned with
183 * packet sizes, but there is one exception when considering overflows.
185 * \section overflow Bulk/interrupt transfer overflows
187 * When requesting data on a bulk endpoint, libusb requires you to supply a
188 * buffer and the maximum number of bytes of data that libusb can put in that
189 * buffer. However, the size of the buffer is not communicated to the device -
190 * the device is just asked to send any amount of data.
192 * There is no problem if the device sends an amount of data that is less than
193 * or equal to the buffer size. libusb reports this condition to you through
194 * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
197 * Problems may occur if the device attempts to send more data than can fit in
198 * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
199 * other behaviour is largely undefined: actual_length may or may not be
200 * accurate, the chunk of data that can fit in the buffer (before overflow)
201 * may or may not have been transferred.
203 * Overflows are nasty, but can be avoided. Even though you were told to
204 * ignore packets above, think about the lower level details: each transfer is
205 * split into packets (typically small, with a maximum size of 512 bytes).
206 * Overflows can only happen if the final packet in an incoming data transfer
207 * is smaller than the actual packet that the device wants to transfer.
208 * Therefore, you will never see an overflow if your transfer buffer size is a
209 * multiple of the endpoint's packet size: the final packet will either
210 * fill up completely or will be only partially filled.
214 * @defgroup asyncio Asynchronous device I/O
216 * This page details libusb's asynchronous (non-blocking) API for USB device
217 * I/O. This interface is very powerful but is also quite complex - you will
218 * need to read this page carefully to understand the necessary considerations
219 * and issues surrounding use of this interface. Simplistic applications
220 * may wish to consider the \ref syncio "synchronous I/O API" instead.
222 * The asynchronous interface is built around the idea of separating transfer
223 * submission and handling of transfer completion (the synchronous model
224 * combines both of these into one). There may be a long delay between
225 * submission and completion, however the asynchronous submission function
226 * is non-blocking so will return control to your application during that
227 * potentially long delay.
229 * \section asyncabstraction Transfer abstraction
231 * For the asynchronous I/O, libusb implements the concept of a generic
232 * transfer entity for all types of I/O (control, bulk, interrupt,
233 * isochronous). The generic transfer object must be treated slightly
234 * differently depending on which type of I/O you are performing with it.
236 * This is represented by the public libusb_transfer structure type.
238 * \section asynctrf Asynchronous transfers
240 * We can view asynchronous I/O as a 5 step process:
241 * -# <b>Allocation</b>: allocate a libusb_transfer
242 * -# <b>Filling</b>: populate the libusb_transfer instance with information
243 * about the transfer you wish to perform
244 * -# <b>Submission</b>: ask libusb to submit the transfer
245 * -# <b>Completion handling</b>: examine transfer results in the
246 * libusb_transfer structure
247 * -# <b>Deallocation</b>: clean up resources
250 * \subsection asyncalloc Allocation
252 * This step involves allocating memory for a USB transfer. This is the
253 * generic transfer object mentioned above. At this stage, the transfer
254 * is "blank" with no details about what type of I/O it will be used for.
256 * Allocation is done with the libusb_alloc_transfer() function. You must use
257 * this function rather than allocating your own transfers.
259 * \subsection asyncfill Filling
261 * This step is where you take a previously allocated transfer and fill it
262 * with information to determine the message type and direction, data buffer,
263 * callback function, etc.
265 * You can either fill the required fields yourself or you can use the
266 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
267 * and libusb_fill_interrupt_transfer().
269 * \subsection asyncsubmit Submission
271 * When you have allocated a transfer and filled it, you can submit it using
272 * libusb_submit_transfer(). This function returns immediately but can be
273 * regarded as firing off the I/O request in the background.
275 * \subsection asynccomplete Completion handling
277 * After a transfer has been submitted, one of four things can happen to it:
279 * - The transfer completes (i.e. some data was transferred)
280 * - The transfer has a timeout and the timeout expires before all data is
282 * - The transfer fails due to an error
283 * - The transfer is cancelled
285 * Each of these will cause the user-specified transfer callback function to
286 * be invoked. It is up to the callback function to determine which of the
287 * above actually happened and to act accordingly.
289 * The user-specified callback is passed a pointer to the libusb_transfer
290 * structure which was used to setup and submit the transfer. At completion
291 * time, libusb has populated this structure with results of the transfer:
292 * success or failure reason, number of bytes of data transferred, etc. See
293 * the libusb_transfer structure documentation for more information.
295 * \subsection Deallocation
297 * When a transfer has completed (i.e. the callback function has been invoked),
298 * you are advised to free the transfer (unless you wish to resubmit it, see
299 * below). Transfers are deallocated with libusb_free_transfer().
301 * It is undefined behaviour to free a transfer which has not completed.
303 * \section asyncresubmit Resubmission
305 * You may be wondering why allocation, filling, and submission are all
306 * separated above where they could reasonably be combined into a single
309 * The reason for separation is to allow you to resubmit transfers without
310 * having to allocate new ones every time. This is especially useful for
311 * common situations dealing with interrupt endpoints - you allocate one
312 * transfer, fill and submit it, and when it returns with results you just
313 * resubmit it for the next interrupt.
315 * \section asynccancel Cancellation
317 * Another advantage of using the asynchronous interface is that you have
318 * the ability to cancel transfers which have not yet completed. This is
319 * done by calling the libusb_cancel_transfer() function.
321 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
322 * cancellation actually completes, the transfer's callback function will
323 * be invoked, and the callback function should check the transfer status to
324 * determine that it was cancelled.
326 * Freeing the transfer after it has been cancelled but before cancellation
327 * has completed will result in undefined behaviour.
329 * When a transfer is cancelled, some of the data may have been transferred.
330 * libusb will communicate this to you in the transfer callback. Do not assume
331 * that no data was transferred.
333 * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
335 * If your device does not have predictable transfer sizes (or it misbehaves),
336 * your application may submit a request for data on an IN endpoint which is
337 * smaller than the data that the device wishes to send. In some circumstances
338 * this will cause an overflow, which is a nasty condition to deal with. See
339 * the \ref packetoverflow page for discussion.
341 * \section asyncctrl Considerations for control transfers
343 * The <tt>libusb_transfer</tt> structure is generic and hence does not
344 * include specific fields for the control-specific setup packet structure.
346 * In order to perform a control transfer, you must place the 8-byte setup
347 * packet at the start of the data buffer. To simplify this, you could
348 * cast the buffer pointer to type struct libusb_control_setup, or you can
349 * use the helper function libusb_fill_control_setup().
351 * The wLength field placed in the setup packet must be the length you would
352 * expect to be sent in the setup packet: the length of the payload that
353 * follows (or the expected maximum number of bytes to receive). However,
354 * the length field of the libusb_transfer object must be the length of
355 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
356 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
358 * If you use the helper functions, this is simplified for you:
359 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
360 * data you are sending/requesting.
361 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
362 * request size as the wLength value (i.e. do not include the extra space you
363 * allocated for the control setup).
364 * -# If this is a host-to-device transfer, place the data to be transferred
365 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
366 * -# Call libusb_fill_control_transfer() to associate the data buffer with
367 * the transfer (and to set the remaining details such as callback and timeout).
368 * - Note that there is no parameter to set the length field of the transfer.
369 * The length is automatically inferred from the wLength field of the setup
371 * -# Submit the transfer.
373 * The multi-byte control setup fields (wValue, wIndex and wLength) must
374 * be given in little-endian byte order (the endianness of the USB bus).
375 * Endianness conversion is transparently handled by
376 * libusb_fill_control_setup() which is documented to accept host-endian
379 * Further considerations are needed when handling transfer completion in
380 * your callback function:
381 * - As you might expect, the setup packet will still be sitting at the start
382 * of the data buffer.
383 * - If this was a device-to-host transfer, the received data will be sitting
384 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
385 * - The actual_length field of the transfer structure is relative to the
386 * wLength of the setup packet, rather than the size of the data buffer. So,
387 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
388 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
389 * transferred in entirity.
391 * To simplify parsing of setup packets and obtaining the data from the
392 * correct offset, you may wish to use the libusb_control_transfer_get_data()
393 * and libusb_control_transfer_get_setup() functions within your transfer
396 * Even though control endpoints do not halt, a completed control transfer
397 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
398 * request was not supported.
400 * \section asyncintr Considerations for interrupt transfers
402 * All interrupt transfers are performed using the polling interval presented
403 * by the bInterval value of the endpoint descriptor.
405 * \section asynciso Considerations for isochronous transfers
407 * Isochronous transfers are more complicated than transfers to
408 * non-isochronous endpoints.
410 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
411 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
413 * During filling, set \ref libusb_transfer::type "type" to
414 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
415 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
416 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
417 * or equal to the number of packets you requested during allocation.
418 * libusb_alloc_transfer() does not set either of these fields for you, given
419 * that you might not even use the transfer on an isochronous endpoint.
421 * Next, populate the length field for the first num_iso_packets entries in
422 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
423 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
424 * packet length is determined by the wMaxPacketSize field in the endpoint
426 * Two functions can help you here:
428 * - libusb_get_max_iso_packet_size() is an easy way to determine the max
429 * packet size for an isochronous endpoint. Note that the maximum packet
430 * size is actually the maximum number of bytes that can be transmitted in
431 * a single microframe, therefore this function multiplies the maximum number
432 * of bytes per transaction by the number of transaction opportunities per
434 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
435 * within a transfer, which is usually what you want.
437 * For outgoing transfers, you'll obviously fill the buffer and populate the
438 * packet descriptors in hope that all the data gets transferred. For incoming
439 * transfers, you must ensure the buffer has sufficient capacity for
440 * the situation where all packets transfer the full amount of requested data.
442 * Completion handling requires some extra consideration. The
443 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
444 * is meaningless and should not be examined; instead you must refer to the
445 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
446 * each individual packet.
448 * The \ref libusb_transfer::status "status" field of the transfer is also a
450 * - If the packets were submitted and the isochronous data microframes
451 * completed normally, status will have value
452 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
453 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
454 * delays are not counted as transfer errors; the transfer.status field may
455 * indicate COMPLETED even if some or all of the packets failed. Refer to
456 * the \ref libusb_iso_packet_descriptor::status "status" field of each
457 * individual packet to determine packet failures.
458 * - The status field will have value
459 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
460 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
461 * - Other transfer status codes occur with normal behaviour.
463 * The data for each packet will be found at an offset into the buffer that
464 * can be calculated as if each prior packet completed in full. The
465 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
466 * functions may help you here.
468 * \section asyncmem Memory caveats
470 * In most circumstances, it is not safe to use stack memory for transfer
471 * buffers. This is because the function that fired off the asynchronous
472 * transfer may return before libusb has finished using the buffer, and when
473 * the function returns it's stack gets destroyed. This is true for both
474 * host-to-device and device-to-host transfers.
476 * The only case in which it is safe to use stack memory is where you can
477 * guarantee that the function owning the stack space for the buffer does not
478 * return until after the transfer's callback function has completed. In every
479 * other case, you need to use heap memory instead.
481 * \section asyncflags Fine control
483 * Through using this asynchronous interface, you may find yourself repeating
484 * a few simple operations many times. You can apply a bitwise OR of certain
485 * flags to a transfer to simplify certain things:
486 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
487 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
488 * less than the requested amount of data being marked with status
489 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
490 * (they would normally be regarded as COMPLETED)
491 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
492 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
493 * buffer when freeing the transfer.
494 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
495 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
496 * transfer after the transfer callback returns.
498 * \section asyncevent Event handling
500 * An asynchronous model requires that libusb perform work at various
501 * points in time - namely processing the results of previously-submitted
502 * transfers and invoking the user-supplied callback function.
504 * This gives rise to the libusb_handle_events() function which your
505 * application must call into when libusb has work do to. This gives libusb
506 * the opportunity to reap pending transfers, invoke callbacks, etc.
508 * There are 2 different approaches to dealing with libusb_handle_events:
510 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
512 * -# Integrate libusb with your application's main event loop. libusb
513 * exposes a set of file descriptors which allow you to do this.
515 * The first approach has the big advantage that it will also work on Windows
516 * were libusb' poll API for select / poll integration is not available. So
517 * if you want to support Windows and use the async API, you must use this
518 * approach, see the \ref eventthread "Using an event handling thread" section
521 * If you prefer a single threaded approach with a single central event loop,
522 * see the \ref poll "polling and timing" section for how to integrate libusb
523 * into your application's main event loop.
525 * \section eventthread Using an event handling thread
527 * Lets begin with stating the obvious: If you're going to use a separate
528 * thread for libusb event handling, your callback functions MUST be
531 * Other then that doing event handling from a separate thread, is mostly
532 * simple. You can use an event thread function as follows:
534 void *event_thread_func(void *ctx)
536 while (event_thread_run)
537 libusb_handle_events(ctx);
543 * There is one caveat though, stopping this thread requires setting the
544 * event_thread_run variable to 0, and after that libusb_handle_events() needs
545 * to return control to event_thread_func. But unless some event happens,
546 * libusb_handle_events() will not return.
548 * There are 2 different ways of dealing with this, depending on if your
549 * application uses libusb' \ref hotplug "hotplug" support or not.
551 * Applications which do not use hotplug support, should not start the event
552 * thread until after their first call to libusb_open(), and should stop the
553 * thread when closing the last open device as follows:
555 void my_close_handle(libusb_device_handle *handle)
558 event_thread_run = 0;
560 libusb_close(handle); // This wakes up libusb_handle_events()
563 pthread_join(event_thread);
569 * Applications using hotplug support should start the thread at program init,
570 * after having successfully called libusb_hotplug_register_callback(), and
571 * should stop the thread at program exit as follows:
573 void my_libusb_exit(void)
575 event_thread_run = 0;
576 libusb_hotplug_deregister_callback(ctx, hotplug_cb_handle); // This wakes up libusb_handle_events()
577 pthread_join(event_thread);
584 * @defgroup poll Polling and timing
586 * This page documents libusb's functions for polling events and timing.
587 * These functions are only necessary for users of the
588 * \ref asyncio "asynchronous API". If you are only using the simpler
589 * \ref syncio "synchronous API" then you do not need to ever call these
592 * The justification for the functionality described here has already been
593 * discussed in the \ref asyncevent "event handling" section of the
594 * asynchronous API documentation. In summary, libusb does not create internal
595 * threads for event processing and hence relies on your application calling
596 * into libusb at certain points in time so that pending events can be handled.
598 * Your main loop is probably already calling poll() or select() or a
599 * variant on a set of file descriptors for other event sources (e.g. keyboard
600 * button presses, mouse movements, network sockets, etc). You then add
601 * libusb's file descriptors to your poll()/select() calls, and when activity
602 * is detected on such descriptors you know it is time to call
603 * libusb_handle_events().
605 * There is one final event handling complication. libusb supports
606 * asynchronous transfers which time out after a specified time period.
608 * On some platforms a timerfd is used, so the timeout handling is just another
609 * fd, on other platforms this requires that libusb is called into at or after
610 * the timeout to handle it. So, in addition to considering libusb's file
611 * descriptors in your main event loop, you must also consider that libusb
612 * sometimes needs to be called into at fixed points in time even when there
613 * is no file descriptor activity, see \ref polltime details.
615 * In order to know precisely when libusb needs to be called into, libusb
616 * offers you a set of pollable file descriptors and information about when
617 * the next timeout expires.
619 * If you are using the asynchronous I/O API, you must take one of the two
620 * following options, otherwise your I/O will not complete.
622 * \section pollsimple The simple option
624 * If your application revolves solely around libusb and does not need to
625 * handle other event sources, you can have a program structure as follows:
628 // find and open device
629 // maybe fire off some initial async I/O
631 while (user_has_not_requested_exit)
632 libusb_handle_events(ctx);
637 * With such a simple main loop, you do not have to worry about managing
638 * sets of file descriptors or handling timeouts. libusb_handle_events() will
639 * handle those details internally.
641 * \section pollmain The more advanced option
643 * \note This functionality is currently only available on Unix-like platforms.
644 * On Windows, libusb_get_pollfds() simply returns NULL. Applications which
645 * want to support Windows are advised to use an \ref eventthread
646 * "event handling thread" instead.
648 * In more advanced applications, you will already have a main loop which
649 * is monitoring other event sources: network sockets, X11 events, mouse
650 * movements, etc. Through exposing a set of file descriptors, libusb is
651 * designed to cleanly integrate into such main loops.
653 * In addition to polling file descriptors for the other event sources, you
654 * take a set of file descriptors from libusb and monitor those too. When you
655 * detect activity on libusb's file descriptors, you call
656 * libusb_handle_events_timeout() in non-blocking mode.
658 * What's more, libusb may also need to handle events at specific moments in
659 * time. No file descriptor activity is generated at these times, so your
660 * own application needs to be continually aware of when the next one of these
661 * moments occurs (through calling libusb_get_next_timeout()), and then it
662 * needs to call libusb_handle_events_timeout() in non-blocking mode when
663 * these moments occur. This means that you need to adjust your
664 * poll()/select() timeout accordingly.
666 * libusb provides you with a set of file descriptors to poll and expects you
667 * to poll all of them, treating them as a single entity. The meaning of each
668 * file descriptor in the set is an internal implementation detail,
669 * platform-dependent and may vary from release to release. Don't try and
670 * interpret the meaning of the file descriptors, just do as libusb indicates,
671 * polling all of them at once.
673 * In pseudo-code, you want something that looks like:
677 libusb_get_pollfds(ctx)
678 while (user has not requested application exit) {
679 libusb_get_next_timeout(ctx);
680 poll(on libusb file descriptors plus any other event sources of interest,
681 using a timeout no larger than the value libusb just suggested)
682 if (poll() indicated activity on libusb file descriptors)
683 libusb_handle_events_timeout(ctx, &zero_tv);
684 if (time has elapsed to or beyond the libusb timeout)
685 libusb_handle_events_timeout(ctx, &zero_tv);
686 // handle events from other sources here
692 * \subsection polltime Notes on time-based events
694 * The above complication with having to track time and call into libusb at
695 * specific moments is a bit of a headache. For maximum compatibility, you do
696 * need to write your main loop as above, but you may decide that you can
697 * restrict the supported platforms of your application and get away with
698 * a more simplistic scheme.
700 * These time-based event complications are \b not required on the following
703 * - Linux, provided that the following version requirements are satisfied:
704 * - Linux v2.6.27 or newer, compiled with timerfd support
705 * - glibc v2.9 or newer
706 * - libusb v1.0.5 or newer
708 * Under these configurations, libusb_get_next_timeout() will \em always return
709 * 0, so your main loop can be simplified to:
713 libusb_get_pollfds(ctx)
714 while (user has not requested application exit) {
715 poll(on libusb file descriptors plus any other event sources of interest,
716 using any timeout that you like)
717 if (poll() indicated activity on libusb file descriptors)
718 libusb_handle_events_timeout(ctx, &zero_tv);
719 // handle events from other sources here
725 * Do remember that if you simplify your main loop to the above, you will
726 * lose compatibility with some platforms (including legacy Linux platforms,
727 * and <em>any future platforms supported by libusb which may have time-based
728 * event requirements</em>). The resultant problems will likely appear as
729 * strange bugs in your application.
731 * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
732 * check to see if it is safe to ignore the time-based event complications.
733 * If your application has taken the shortcut of ignoring libusb's next timeout
734 * in your main loop, then you are advised to check the return value of
735 * libusb_pollfds_handle_timeouts() during application startup, and to abort
736 * if the platform does suffer from these timing complications.
738 * \subsection fdsetchange Changes in the file descriptor set
740 * The set of file descriptors that libusb uses as event sources may change
741 * during the life of your application. Rather than having to repeatedly
742 * call libusb_get_pollfds(), you can set up notification functions for when
743 * the file descriptor set changes using libusb_set_pollfd_notifiers().
745 * \subsection mtissues Multi-threaded considerations
747 * Unfortunately, the situation is complicated further when multiple threads
748 * come into play. If two threads are monitoring the same file descriptors,
749 * the fact that only one thread will be woken up when an event occurs causes
752 * The events lock, event waiters lock, and libusb_handle_events_locked()
753 * entities are added to solve these problems. You do not need to be concerned
754 * with these entities otherwise.
756 * See the extra documentation: \ref mtasync
759 /** \page mtasync Multi-threaded applications and asynchronous I/O
761 * libusb is a thread-safe library, but extra considerations must be applied
762 * to applications which interact with libusb from multiple threads.
764 * The underlying issue that must be addressed is that all libusb I/O
765 * revolves around monitoring file descriptors through the poll()/select()
766 * system calls. This is directly exposed at the
767 * \ref asyncio "asynchronous interface" but it is important to note that the
768 * \ref syncio "synchronous interface" is implemented on top of the
769 * asynchonrous interface, therefore the same considerations apply.
771 * The issue is that if two or more threads are concurrently calling poll()
772 * or select() on libusb's file descriptors then only one of those threads
773 * will be woken up when an event arrives. The others will be completely
774 * oblivious that anything has happened.
776 * Consider the following pseudo-code, which submits an asynchronous transfer
777 * then waits for its completion. This style is one way you could implement a
778 * synchronous interface on top of the asynchronous interface (and libusb
779 * does something similar, albeit more advanced due to the complications
780 * explained on this page).
783 void cb(struct libusb_transfer *transfer)
785 int *completed = transfer->user_data;
790 struct libusb_transfer *transfer;
791 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE] __attribute__ ((aligned (2)));
794 transfer = libusb_alloc_transfer(0);
795 libusb_fill_control_setup(buffer,
796 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
797 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
798 libusb_submit_transfer(transfer);
801 poll(libusb file descriptors, 120*1000);
802 if (poll indicates activity)
803 libusb_handle_events_timeout(ctx, &zero_tv);
805 printf("completed!");
810 * Here we are <em>serializing</em> completion of an asynchronous event
811 * against a condition - the condition being completion of a specific transfer.
812 * The poll() loop has a long timeout to minimize CPU usage during situations
813 * when nothing is happening (it could reasonably be unlimited).
815 * If this is the only thread that is polling libusb's file descriptors, there
816 * is no problem: there is no danger that another thread will swallow up the
817 * event that we are interested in. On the other hand, if there is another
818 * thread polling the same descriptors, there is a chance that it will receive
819 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
820 * will only realise that the transfer has completed on the next iteration of
821 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
822 * undesirable, and don't even think about using short timeouts to circumvent
825 * The solution here is to ensure that no two threads are ever polling the
826 * file descriptors at the same time. A naive implementation of this would
827 * impact the capabilities of the library, so libusb offers the scheme
828 * documented below to ensure no loss of functionality.
830 * Before we go any further, it is worth mentioning that all libusb-wrapped
831 * event handling procedures fully adhere to the scheme documented below.
832 * This includes libusb_handle_events() and its variants, and all the
833 * synchronous I/O functions - libusb hides this headache from you.
835 * \section Using libusb_handle_events() from multiple threads
837 * Even when only using libusb_handle_events() and synchronous I/O functions,
838 * you can still have a race condition. You might be tempted to solve the
839 * above with libusb_handle_events() like so:
842 libusb_submit_transfer(transfer);
845 libusb_handle_events(ctx);
847 printf("completed!");
850 * This however has a race between the checking of completed and
851 * libusb_handle_events() acquiring the events lock, so another thread
852 * could have completed the transfer, resulting in this thread hanging
853 * until either a timeout or another event occurs. See also commit
854 * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
855 * synchronous API implementation of libusb.
857 * Fixing this race requires checking the variable completed only after
858 * taking the event lock, which defeats the concept of just calling
859 * libusb_handle_events() without worrying about locking. This is why
860 * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
861 * and libusb_handle_events_completed() functions, which handles doing the
862 * completion check for you after they have acquired the lock:
865 libusb_submit_transfer(transfer);
868 libusb_handle_events_completed(ctx, &completed);
870 printf("completed!");
873 * This nicely fixes the race in our example. Note that if all you want to
874 * do is submit a single transfer and wait for its completion, then using
875 * one of the synchronous I/O functions is much easier.
877 * \section eventlock The events lock
879 * The problem is when we consider the fact that libusb exposes file
880 * descriptors to allow for you to integrate asynchronous USB I/O into
881 * existing main loops, effectively allowing you to do some work behind
882 * libusb's back. If you do take libusb's file descriptors and pass them to
883 * poll()/select() yourself, you need to be aware of the associated issues.
885 * The first concept to be introduced is the events lock. The events lock
886 * is used to serialize threads that want to handle events, such that only
887 * one thread is handling events at any one time.
889 * You must take the events lock before polling libusb file descriptors,
890 * using libusb_lock_events(). You must release the lock as soon as you have
891 * aborted your poll()/select() loop, using libusb_unlock_events().
893 * \section threadwait Letting other threads do the work for you
895 * Although the events lock is a critical part of the solution, it is not
896 * enough on it's own. You might wonder if the following is sufficient...
898 libusb_lock_events(ctx);
900 poll(libusb file descriptors, 120*1000);
901 if (poll indicates activity)
902 libusb_handle_events_timeout(ctx, &zero_tv);
904 libusb_unlock_events(ctx);
906 * ...and the answer is that it is not. This is because the transfer in the
907 * code shown above may take a long time (say 30 seconds) to complete, and
908 * the lock is not released until the transfer is completed.
910 * Another thread with similar code that wants to do event handling may be
911 * working with a transfer that completes after a few milliseconds. Despite
912 * having such a quick completion time, the other thread cannot check that
913 * status of its transfer until the code above has finished (30 seconds later)
914 * due to contention on the lock.
916 * To solve this, libusb offers you a mechanism to determine when another
917 * thread is handling events. It also offers a mechanism to block your thread
918 * until the event handling thread has completed an event (and this mechanism
919 * does not involve polling of file descriptors).
921 * After determining that another thread is currently handling events, you
922 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
923 * You then re-check that some other thread is still handling events, and if
924 * so, you call libusb_wait_for_event().
926 * libusb_wait_for_event() puts your application to sleep until an event
927 * occurs, or until a thread releases the events lock. When either of these
928 * things happen, your thread is woken up, and should re-check the condition
929 * it was waiting on. It should also re-check that another thread is handling
930 * events, and if not, it should start handling events itself.
932 * This looks like the following, as pseudo-code:
935 if (libusb_try_lock_events(ctx) == 0) {
936 // we obtained the event lock: do our own event handling
938 if (!libusb_event_handling_ok(ctx)) {
939 libusb_unlock_events(ctx);
942 poll(libusb file descriptors, 120*1000);
943 if (poll indicates activity)
944 libusb_handle_events_locked(ctx, 0);
946 libusb_unlock_events(ctx);
948 // another thread is doing event handling. wait for it to signal us that
949 // an event has completed
950 libusb_lock_event_waiters(ctx);
953 // now that we have the event waiters lock, double check that another
954 // thread is still handling events for us. (it may have ceased handling
955 // events in the time it took us to reach this point)
956 if (!libusb_event_handler_active(ctx)) {
957 // whoever was handling events is no longer doing so, try again
958 libusb_unlock_event_waiters(ctx);
962 libusb_wait_for_event(ctx, NULL);
964 libusb_unlock_event_waiters(ctx);
966 printf("completed!\n");
969 * A naive look at the above code may suggest that this can only support
970 * one event waiter (hence a total of 2 competing threads, the other doing
971 * event handling), because the event waiter seems to have taken the event
972 * waiters lock while waiting for an event. However, the system does support
973 * multiple event waiters, because libusb_wait_for_event() actually drops
974 * the lock while waiting, and reaquires it before continuing.
976 * We have now implemented code which can dynamically handle situations where
977 * nobody is handling events (so we should do it ourselves), and it can also
978 * handle situations where another thread is doing event handling (so we can
979 * piggyback onto them). It is also equipped to handle a combination of
980 * the two, for example, another thread is doing event handling, but for
981 * whatever reason it stops doing so before our condition is met, so we take
982 * over the event handling.
984 * Four functions were introduced in the above pseudo-code. Their importance
985 * should be apparent from the code shown above.
986 * -# libusb_try_lock_events() is a non-blocking function which attempts
987 * to acquire the events lock but returns a failure code if it is contended.
988 * -# libusb_event_handling_ok() checks that libusb is still happy for your
989 * thread to be performing event handling. Sometimes, libusb needs to
990 * interrupt the event handler, and this is how you can check if you have
991 * been interrupted. If this function returns 0, the correct behaviour is
992 * for you to give up the event handling lock, and then to repeat the cycle.
993 * The following libusb_try_lock_events() will fail, so you will become an
994 * events waiter. For more information on this, read \ref fullstory below.
995 * -# libusb_handle_events_locked() is a variant of
996 * libusb_handle_events_timeout() that you can call while holding the
997 * events lock. libusb_handle_events_timeout() itself implements similar
998 * logic to the above, so be sure not to call it when you are
999 * "working behind libusb's back", as is the case here.
1000 * -# libusb_event_handler_active() determines if someone is currently
1001 * holding the events lock
1003 * You might be wondering why there is no function to wake up all threads
1004 * blocked on libusb_wait_for_event(). This is because libusb can do this
1005 * internally: it will wake up all such threads when someone calls
1006 * libusb_unlock_events() or when a transfer completes (at the point after its
1007 * callback has returned).
1009 * \subsection fullstory The full story
1011 * The above explanation should be enough to get you going, but if you're
1012 * really thinking through the issues then you may be left with some more
1013 * questions regarding libusb's internals. If you're curious, read on, and if
1014 * not, skip to the next section to avoid confusing yourself!
1016 * The immediate question that may spring to mind is: what if one thread
1017 * modifies the set of file descriptors that need to be polled while another
1018 * thread is doing event handling?
1020 * There are 2 situations in which this may happen.
1021 * -# libusb_open() will add another file descriptor to the poll set,
1022 * therefore it is desirable to interrupt the event handler so that it
1023 * restarts, picking up the new descriptor.
1024 * -# libusb_close() will remove a file descriptor from the poll set. There
1025 * are all kinds of race conditions that could arise here, so it is
1026 * important that nobody is doing event handling at this time.
1028 * libusb handles these issues internally, so application developers do not
1029 * have to stop their event handlers while opening/closing devices. Here's how
1030 * it works, focusing on the libusb_close() situation first:
1032 * -# During initialization, libusb opens an internal pipe, and it adds the read
1033 * end of this pipe to the set of file descriptors to be polled.
1034 * -# During libusb_close(), libusb writes some dummy data on this control pipe.
1035 * This immediately interrupts the event handler. libusb also records
1036 * internally that it is trying to interrupt event handlers for this
1037 * high-priority event.
1038 * -# At this point, some of the functions described above start behaving
1040 * - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
1041 * OK for event handling to continue.
1042 * - libusb_try_lock_events() starts returning 1, indicating that another
1043 * thread holds the event handling lock, even if the lock is uncontended.
1044 * - libusb_event_handler_active() starts returning 1, indicating that
1045 * another thread is doing event handling, even if that is not true.
1046 * -# The above changes in behaviour result in the event handler stopping and
1047 * giving up the events lock very quickly, giving the high-priority
1048 * libusb_close() operation a "free ride" to acquire the events lock. All
1049 * threads that are competing to do event handling become event waiters.
1050 * -# With the events lock held inside libusb_close(), libusb can safely remove
1051 * a file descriptor from the poll set, in the safety of knowledge that
1052 * nobody is polling those descriptors or trying to access the poll set.
1053 * -# After obtaining the events lock, the close operation completes very
1054 * quickly (usually a matter of milliseconds) and then immediately releases
1056 * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
1057 * reverts to the original, documented behaviour.
1058 * -# The release of the events lock causes the threads that are waiting for
1059 * events to be woken up and to start competing to become event handlers
1060 * again. One of them will succeed; it will then re-obtain the list of poll
1061 * descriptors, and USB I/O will then continue as normal.
1063 * libusb_open() is similar, and is actually a more simplistic case. Upon a
1064 * call to libusb_open():
1066 * -# The device is opened and a file descriptor is added to the poll set.
1067 * -# libusb sends some dummy data on the control pipe, and records that it
1068 * is trying to modify the poll descriptor set.
1069 * -# The event handler is interrupted, and the same behaviour change as for
1070 * libusb_close() takes effect, causing all event handling threads to become
1072 * -# The libusb_open() implementation takes its free ride to the events lock.
1073 * -# Happy that it has successfully paused the events handler, libusb_open()
1074 * releases the events lock.
1075 * -# The event waiter threads are all woken up and compete to become event
1076 * handlers again. The one that succeeds will obtain the list of poll
1077 * descriptors again, which will include the addition of the new device.
1079 * \subsection concl Closing remarks
1081 * The above may seem a little complicated, but hopefully I have made it clear
1082 * why such complications are necessary. Also, do not forget that this only
1083 * applies to applications that take libusb's file descriptors and integrate
1084 * them into their own polling loops.
1086 * You may decide that it is OK for your multi-threaded application to ignore
1087 * some of the rules and locks detailed above, because you don't think that
1088 * two threads can ever be polling the descriptors at the same time. If that
1089 * is the case, then that's good news for you because you don't have to worry.
1090 * But be careful here; remember that the synchronous I/O functions do event
1091 * handling internally. If you have one thread doing event handling in a loop
1092 * (without implementing the rules and locking semantics documented above)
1093 * and another trying to send a synchronous USB transfer, you will end up with
1094 * two threads monitoring the same descriptors, and the above-described
1095 * undesirable behaviour occuring. The solution is for your polling thread to
1096 * play by the rules; the synchronous I/O functions do so, and this will result
1097 * in them getting along in perfect harmony.
1099 * If you do have a dedicated thread doing event handling, it is perfectly
1100 * legal for it to take the event handling lock for long periods of time. Any
1101 * synchronous I/O functions you call from other threads will transparently
1102 * fall back to the "event waiters" mechanism detailed above. The only
1103 * consideration that your event handling thread must apply is the one related
1104 * to libusb_event_handling_ok(): you must call this before every poll(), and
1105 * give up the events lock if instructed.
1108 int usbi_io_init(struct libusb_context *ctx) {
1112 usbi_mutex_init(&ctx->flying_transfers_lock, NULL);
1113 usbi_mutex_init(&ctx->pollfds_lock, NULL);
1114 usbi_mutex_init(&ctx->pollfd_modify_lock, NULL);
1115 usbi_mutex_init_recursive(&ctx->events_lock, NULL);
1116 usbi_mutex_init(&ctx->event_waiters_lock, NULL);
1117 usbi_cond_init(&ctx->event_waiters_cond, NULL);
1118 list_init(&ctx->flying_transfers);
1119 list_init(&ctx->pollfds);
1121 /* FIXME should use an eventfd on kernels that support it */
1122 r = usbi_pipe(ctx->ctrl_pipe);
1123 if (UNLIKELY(r < 0)) {
1124 r = LIBUSB_ERROR_OTHER;
1128 r = usbi_add_pollfd(ctx, ctx->ctrl_pipe[0], POLLIN);
1129 if (UNLIKELY(r < 0))
1130 goto err_close_pipe;
1132 /* create hotplug pipe */
1133 r = usbi_pipe(ctx->hotplug_pipe);
1134 if (UNLIKELY(r < 0)) {
1135 r = LIBUSB_ERROR_OTHER;
1139 r = usbi_add_pollfd(ctx, ctx->hotplug_pipe[0], POLLIN);
1140 if (UNLIKELY(r < 0))
1141 goto err_close_hp_pipe;
1143 #ifdef USBI_TIMERFD_AVAILABLE
1144 ctx->timerfd = timerfd_create(usbi_backend->get_timerfd_clockid(),
1146 if (UNLIKELY(ctx->timerfd >= 0)) {
1147 usbi_dbg("using timerfd for timeouts");
1148 r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
1149 if (UNLIKELY(r < 0)) {
1150 usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
1151 close(ctx->timerfd);
1152 goto err_close_hp_pipe;
1155 usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
1160 return LIBUSB_SUCCESS;
1163 usbi_close(ctx->hotplug_pipe[0]);
1164 usbi_close(ctx->hotplug_pipe[1]);
1166 usbi_close(ctx->ctrl_pipe[0]);
1167 usbi_close(ctx->ctrl_pipe[1]);
1169 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1170 usbi_mutex_destroy(&ctx->pollfds_lock);
1171 usbi_mutex_destroy(&ctx->pollfd_modify_lock);
1172 usbi_mutex_destroy(&ctx->events_lock);
1173 usbi_mutex_destroy(&ctx->event_waiters_lock);
1174 usbi_cond_destroy(&ctx->event_waiters_cond);
1178 void usbi_io_exit(struct libusb_context *ctx) {
1180 usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
1181 usbi_close(ctx->ctrl_pipe[0]);
1182 usbi_close(ctx->ctrl_pipe[1]);
1183 usbi_remove_pollfd(ctx, ctx->hotplug_pipe[0]);
1184 usbi_close(ctx->hotplug_pipe[0]);
1185 usbi_close(ctx->hotplug_pipe[1]);
1186 #ifdef USBI_TIMERFD_AVAILABLE
1187 if (usbi_using_timerfd(ctx)) {
1188 usbi_remove_pollfd(ctx, ctx->timerfd);
1189 close(ctx->timerfd);
1192 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1193 usbi_mutex_destroy(&ctx->pollfds_lock);
1194 usbi_mutex_destroy(&ctx->pollfd_modify_lock);
1195 usbi_mutex_destroy(&ctx->events_lock);
1196 usbi_mutex_destroy(&ctx->event_waiters_lock);
1197 usbi_cond_destroy(&ctx->event_waiters_cond);
1200 static int calculate_timeout(struct usbi_transfer *transfer) {
1203 struct timespec current_time;
1204 unsigned int timeout =
1205 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
1208 return LIBUSB_SUCCESS;
1210 r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, ¤t_time);
1211 if (UNLIKELY(r < 0)) {
1212 usbi_err(ITRANSFER_CTX(transfer),
1213 "failed to read monotonic clock, errno=%d", errno);
1217 current_time.tv_sec += timeout / 1000;
1218 current_time.tv_nsec += (timeout % 1000) * 1000000;
1220 while (current_time.tv_nsec >= 1000000000) {
1221 current_time.tv_nsec -= 1000000000;
1222 current_time.tv_sec++;
1225 TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
1226 return LIBUSB_SUCCESS;
1229 /* add a transfer to the (timeout-sorted) active transfers list.
1230 * Callers of this function must hold the flying_transfers_lock.
1231 * This function *always* adds the transfer to the flying_transfers list,
1232 * it will return non 0 if it fails to update the timer, but even then the
1233 * transfer is added to the flying_transfers list. */
1234 static int add_to_flying_list(struct usbi_transfer *transfer) {
1236 struct usbi_transfer *cur;
1237 struct timeval *timeout = &transfer->timeout;
1238 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1242 /* if we have no other flying transfers, start the list with this one */
1243 if (list_empty(&ctx->flying_transfers)) {
1244 list_add(&transfer->list, &ctx->flying_transfers);
1248 /* if we have infinite timeout, append to end of list */
1249 if (!timerisset(timeout)) {
1250 list_add_tail(&transfer->list, &ctx->flying_transfers);
1251 /* first is irrelevant in this case */
1255 /* otherwise, find appropriate place in list */
1256 list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
1257 /* find first timeout that occurs after the transfer in question */
1258 struct timeval *cur_tv = &cur->timeout;
1260 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
1261 (cur_tv->tv_sec == timeout->tv_sec &&
1262 cur_tv->tv_usec > timeout->tv_usec)) {
1263 list_add_tail(&transfer->list, &cur->list);
1268 /* first is 0 at this stage (list not empty) */
1270 /* otherwise we need to be inserted at the end */
1271 list_add_tail(&transfer->list, &ctx->flying_transfers);
1273 #ifdef USBI_TIMERFD_AVAILABLE
1274 if (first && usbi_using_timerfd(ctx) && timerisset(timeout)) {
1275 /* if this transfer has the lowest timeout of all active transfers,
1276 * rearm the timerfd with this transfer's timeout */
1277 const struct itimerspec it = { {0, 0},
1278 { timeout->tv_sec, timeout->tv_usec * 1000 } };
1279 usbi_dbg("arm timerfd for timeout in %dms (first in line)",
1280 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1281 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1283 usbi_warn(ctx, "failed to arm first timerfd (errno %d)", errno);
1284 r = LIBUSB_ERROR_OTHER;
1294 /** \ingroup asyncio
1295 * Allocate a libusb transfer with a specified number of isochronous packet
1296 * descriptors. The returned transfer is pre-initialized for you. When the new
1297 * transfer is no longer needed, it should be freed with
1298 * libusb_free_transfer().
1300 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
1301 * interrupt) should specify an iso_packets count of zero.
1303 * For transfers intended for isochronous endpoints, specify an appropriate
1304 * number of packet descriptors to be allocated as part of the transfer.
1305 * The returned transfer is not specially initialized for isochronous I/O;
1306 * you are still required to set the
1307 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
1308 * \ref libusb_transfer::type "type" fields accordingly.
1310 * It is safe to allocate a transfer with some isochronous packets and then
1311 * use it on a non-isochronous endpoint. If you do this, ensure that at time
1312 * of submission, num_iso_packets is 0 and that type is set appropriately.
1314 * \param iso_packets number of isochronous packet descriptors to allocate
1315 * \returns a newly allocated transfer, or NULL on error
1318 struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
1321 size_t os_alloc_size = usbi_backend->transfer_priv_size
1322 + (usbi_backend->add_iso_packet_size * iso_packets);
1323 size_t alloc_size = sizeof(struct usbi_transfer)
1324 + sizeof(struct libusb_transfer)
1325 + (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
1327 struct usbi_transfer *itransfer = calloc(1, alloc_size);
1328 if (UNLIKELY(!itransfer))
1331 itransfer->num_iso_packets = iso_packets;
1332 usbi_mutex_init(&itransfer->lock, NULL);
1333 return USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1336 /** \ingroup asyncio
1337 * Free a transfer structure. This should be called for all transfers
1338 * allocated with libusb_alloc_transfer().
1340 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
1341 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
1342 * non-NULL, this function will also free the transfer buffer using the
1343 * standard system memory allocator (e.g. free()).
1345 * It is legal to call this function with a NULL transfer. In this case,
1346 * the function will simply return safely.
1348 * It is not legal to free an active transfer (one which has been submitted
1349 * and has not yet completed).
1351 * \param transfer the transfer to free
1353 void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer) {
1355 struct usbi_transfer *itransfer;
1356 if (UNLIKELY(!transfer))
1359 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
1360 free(transfer->buffer);
1362 itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1363 usbi_mutex_destroy(&itransfer->lock);
1365 transfer->user_data = NULL; // XXX
1368 #ifdef USBI_TIMERFD_AVAILABLE
1369 static int disarm_timerfd(struct libusb_context *ctx) {
1371 const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
1375 r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
1376 if (UNLIKELY(r < 0))
1377 return LIBUSB_ERROR_OTHER;
1379 return LIBUSB_SUCCESS;
1382 /* iterates through the flying transfers, and rearms the timerfd based on the
1383 * next upcoming timeout.
1384 * must be called with flying_list locked.
1385 * returns 0 if there was no timeout to arm, 1 if the next timeout was armed,
1386 * or a LIBUSB_ERROR code on failure.
1388 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx) {
1390 struct usbi_transfer *transfer;
1392 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1393 struct timeval *cur_tv = &transfer->timeout;
1395 /* if we've reached transfers of infinite timeout, then we have no
1397 if (!timerisset(cur_tv))
1400 /* act on first transfer that is not already cancelled */
1401 if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
1403 const struct itimerspec it = { {0, 0},
1404 { cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
1405 usbi_dbg("next timeout originally %dms", USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1406 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1408 return LIBUSB_ERROR_OTHER;
1414 return disarm_timerfd(ctx);
1417 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx) {
1420 return LIBUSB_SUCCESS;
1424 /** \ingroup asyncio
1425 * Submit a transfer. This function will fire off the USB transfer and then
1426 * return immediately.
1428 * \param transfer the transfer to submit
1429 * \returns 0 on success
1430 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
1431 * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
1432 * \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
1433 * by the operating system.
1434 * \returns another LIBUSB_ERROR code on other failure
1436 int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer) {
1438 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1439 struct usbi_transfer *itransfer =
1440 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1444 usbi_mutex_lock(&ctx->flying_transfers_lock);
1445 usbi_mutex_lock(&itransfer->lock);
1447 itransfer->transferred = 0;
1448 itransfer->flags = 0;
1449 r = calculate_timeout(itransfer);
1450 if (UNLIKELY(r < 0)) {
1451 r = LIBUSB_ERROR_OTHER;
1455 r = add_to_flying_list(itransfer);
1456 if (LIKELY(r == LIBUSB_SUCCESS)) {
1457 r = usbi_backend->submit_transfer(itransfer);
1459 if (UNLIKELY(r != LIBUSB_SUCCESS)) {
1460 list_del(&itransfer->list);
1461 arm_timerfd_for_next_timeout(ctx);
1463 /* keep a reference to this device */
1464 libusb_ref_device(transfer->dev_handle->dev);
1467 updated_fds = (itransfer->flags & USBI_TRANSFER_UPDATED_FDS);
1469 usbi_mutex_unlock(&itransfer->lock);
1470 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1472 usbi_fd_notification(ctx);
1476 /** \ingroup asyncio
1477 * Asynchronously cancel a previously submitted transfer.
1478 * This function returns immediately, but this does not indicate cancellation
1479 * is complete. Your callback function will be invoked at some later time
1480 * with a transfer status of
1481 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
1482 * "LIBUSB_TRANSFER_CANCELLED."
1484 * \param transfer the transfer to cancel
1485 * \returns 0 on success
1486 * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is already complete or
1488 * \returns a LIBUSB_ERROR code on failure
1490 int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer) {
1492 struct usbi_transfer *itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1496 usbi_mutex_lock(&itransfer->lock);
1498 r = usbi_backend->cancel_transfer(itransfer);
1499 if (UNLIKELY(r < 0)) {
1500 if (r != LIBUSB_ERROR_NOT_FOUND &&
1501 r != LIBUSB_ERROR_NO_DEVICE) {
1502 usbi_err(TRANSFER_CTX(transfer), "cancel transfer failed error %d", r);
1504 usbi_dbg("cancel transfer failed error %d", r);
1506 if (r == LIBUSB_ERROR_NO_DEVICE)
1507 itransfer->flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
1510 itransfer->flags |= USBI_TRANSFER_CANCELLING;
1512 usbi_mutex_unlock(&itransfer->lock);
1516 /** \ingroup asyncio
1517 * Set a transfers bulk stream id. Note users are advised to use
1518 * libusb_fill_bulk_stream_transfer() instead of calling this function
1521 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1523 * \param transfer the transfer to set the stream id for
1524 * \param stream_id the stream id to set
1525 * \see libusb_alloc_streams()
1527 void API_EXPORTED libusb_transfer_set_stream_id(
1528 struct libusb_transfer *transfer, uint32_t stream_id)
1530 struct usbi_transfer *itransfer =
1531 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1533 itransfer->stream_id = stream_id;
1536 /** \ingroup asyncio
1537 * Get a transfers bulk stream id.
1539 * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103
1541 * \param transfer the transfer to get the stream id for
1542 * \returns the stream id for the transfer
1544 uint32_t API_EXPORTED libusb_transfer_get_stream_id(
1545 struct libusb_transfer *transfer)
1547 struct usbi_transfer *itransfer =
1548 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1550 return itransfer->stream_id;
1553 /* Handle completion of a transfer (completion might be an error condition).
1554 * This will invoke the user-supplied callback function, which may end up
1555 * freeing the transfer. Therefore you cannot use the transfer structure
1556 * after calling this function, and you should free all backend-specific
1557 * data before calling it.
1558 * Do not call this function with the usbi_transfer lock held. User-specified
1559 * callback functions may attempt to directly resubmit the transfer, which
1560 * will attempt to take the lock. */
1561 int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1562 enum libusb_transfer_status status) {
1564 struct libusb_transfer *transfer =
1565 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1566 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1567 struct libusb_device_handle *handle = transfer->dev_handle;
1571 /* FIXME: could be more intelligent with the timerfd here. we don't need
1572 * to disarm the timerfd if there was no timer running, and we only need
1573 * to rearm the timerfd if the transfer that expired was the one with
1574 * the shortest timeout. */
1576 usbi_mutex_lock(&ctx->flying_transfers_lock);
1578 list_del(&itransfer->list);
1579 if (usbi_using_timerfd(ctx))
1580 r = arm_timerfd_for_next_timeout(ctx);
1582 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1583 if (usbi_using_timerfd(ctx) && (r < 0))
1586 if (status == LIBUSB_TRANSFER_COMPLETED
1587 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1588 int rqlen = transfer->length;
1589 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1590 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1591 if (rqlen != itransfer->transferred) { // XXX itransfer->transferred is almost always zero on iso transfer mode...
1592 usbi_dbg("interpreting short transfer as error");
1593 LOGI("interpreting short transfer as error:rqlen=%d,transferred=%d", rqlen, itransfer->transferred);
1594 status = LIBUSB_TRANSFER_ERROR;
1598 flags = transfer->flags;
1599 transfer->status = status;
1600 transfer->actual_length = itransfer->transferred; // XXX therefore transfer->actual_length is also almost always zero on iso transfer mode
1601 usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
1602 if LIKELY(transfer->callback)
1603 transfer->callback(transfer);
1604 /* transfer might have been freed by the above call, do not use from
1606 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1607 libusb_free_transfer(transfer);
1608 usbi_mutex_lock(&ctx->event_waiters_lock);
1610 usbi_cond_broadcast(&ctx->event_waiters_cond);
1612 usbi_mutex_unlock(&ctx->event_waiters_lock);
1613 libusb_unref_device(handle->dev);
1614 return LIBUSB_SUCCESS;
1617 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1618 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1619 * transfers exist here.
1620 * Do not call this function with the usbi_transfer lock held. User-specified
1621 * callback functions may attempt to directly resubmit the transfer, which
1622 * will attempt to take the lock. */
1623 int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer) {
1625 /* if the URB was cancelled due to timeout, report timeout to the user */
1626 if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
1627 usbi_dbg("detected timeout cancellation");
1628 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
1631 /* otherwise its a normal async cancel */
1632 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
1636 * Attempt to acquire the event handling lock. This lock is used to ensure that
1637 * only one thread is monitoring libusb event sources at any one time.
1639 * You only need to use this lock if you are developing an application
1640 * which calls poll() or select() on libusb's file descriptors directly.
1641 * If you stick to libusb's event handling loop functions (e.g.
1642 * libusb_handle_events()) then you do not need to be concerned with this
1645 * While holding this lock, you are trusted to actually be handling events.
1646 * If you are no longer handling events, you must call libusb_unlock_events()
1647 * as soon as possible.
1649 * \param ctx the context to operate on, or NULL for the default context
1650 * \returns 0 if the lock was obtained successfully
1651 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1654 int API_EXPORTED libusb_try_lock_events(libusb_context *ctx) {
1658 USBI_GET_CONTEXT(ctx);
1660 /* is someone else waiting to modify poll fds? if so, don't let this thread
1661 * start event handling */
1662 usbi_mutex_lock(&ctx->pollfd_modify_lock);
1664 ru = ctx->pollfd_modify;
1666 usbi_mutex_unlock(&ctx->pollfd_modify_lock);
1668 usbi_dbg("someone else is modifying poll fds");
1672 r = usbi_mutex_trylock(&ctx->events_lock);
1676 ctx->event_handler_active = 1;
1677 return LIBUSB_SUCCESS;
1681 * Acquire the event handling lock, blocking until successful acquisition if
1682 * it is contended. This lock is used to ensure that only one thread is
1683 * monitoring libusb event sources at any one time.
1685 * You only need to use this lock if you are developing an application
1686 * which calls poll() or select() on libusb's file descriptors directly.
1687 * If you stick to libusb's event handling loop functions (e.g.
1688 * libusb_handle_events()) then you do not need to be concerned with this
1691 * While holding this lock, you are trusted to actually be handling events.
1692 * If you are no longer handling events, you must call libusb_unlock_events()
1693 * as soon as possible.
1695 * \param ctx the context to operate on, or NULL for the default context
1698 void API_EXPORTED libusb_lock_events(libusb_context *ctx) {
1700 USBI_GET_CONTEXT(ctx);
1701 usbi_mutex_lock(&ctx->events_lock);
1702 ctx->event_handler_active = 1;
1706 * Release the lock previously acquired with libusb_try_lock_events() or
1707 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1708 * on libusb_wait_for_event().
1710 * \param ctx the context to operate on, or NULL for the default context
1713 void API_EXPORTED libusb_unlock_events(libusb_context *ctx) {
1715 USBI_GET_CONTEXT(ctx);
1716 ctx->event_handler_active = 0;
1717 usbi_mutex_unlock(&ctx->events_lock);
1719 /* FIXME: perhaps we should be a bit more efficient by not broadcasting
1720 * the availability of the events lock when we are modifying pollfds
1721 * (check ctx->pollfd_modify)? */
1722 usbi_mutex_lock(&ctx->event_waiters_lock);
1724 usbi_cond_broadcast(&ctx->event_waiters_cond);
1726 usbi_mutex_unlock(&ctx->event_waiters_lock);
1730 * Determine if it is still OK for this thread to be doing event handling.
1732 * Sometimes, libusb needs to temporarily pause all event handlers, and this
1733 * is the function you should use before polling file descriptors to see if
1736 * If this function instructs your thread to give up the events lock, you
1737 * should just continue the usual logic that is documented in \ref mtasync.
1738 * On the next iteration, your thread will fail to obtain the events lock,
1739 * and will hence become an event waiter.
1741 * This function should be called while the events lock is held: you don't
1742 * need to worry about the results of this function if your thread is not
1743 * the current event handler.
1745 * \param ctx the context to operate on, or NULL for the default context
1746 * \returns 1 if event handling can start or continue
1747 * \returns 0 if this thread must give up the events lock
1748 * \ref fullstory "Multi-threaded I/O: the full story"
1750 int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx) {
1753 USBI_GET_CONTEXT(ctx);
1755 /* is someone else waiting to modify poll fds? if so, don't let this thread
1756 * continue event handling */
1757 usbi_mutex_lock(&ctx->pollfd_modify_lock);
1759 r = ctx->pollfd_modify;
1761 usbi_mutex_unlock(&ctx->pollfd_modify_lock);
1763 usbi_dbg("someone else is modifying poll fds");
1764 return LIBUSB_SUCCESS;
1772 * Determine if an active thread is handling events (i.e. if anyone is holding
1773 * the event handling lock).
1775 * \param ctx the context to operate on, or NULL for the default context
1776 * \returns 1 if a thread is handling events
1777 * \returns 0 if there are no threads currently handling events
1780 int API_EXPORTED libusb_event_handler_active(libusb_context *ctx) {
1783 USBI_GET_CONTEXT(ctx);
1785 /* is someone else waiting to modify poll fds? if so, don't let this thread
1786 * start event handling -- indicate that event handling is happening */
1787 usbi_mutex_lock(&ctx->pollfd_modify_lock);
1789 r = ctx->pollfd_modify;
1791 usbi_mutex_unlock(&ctx->pollfd_modify_lock);
1793 usbi_dbg("someone else is modifying poll fds");
1797 return ctx->event_handler_active;
1801 * Acquire the event waiters lock. This lock is designed to be obtained under
1802 * the situation where you want to be aware when events are completed, but
1803 * some other thread is event handling so calling libusb_handle_events() is not
1806 * You then obtain this lock, re-check that another thread is still handling
1807 * events, then call libusb_wait_for_event().
1809 * You only need to use this lock if you are developing an application
1810 * which calls poll() or select() on libusb's file descriptors directly,
1811 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1812 * If you stick to libusb's event handling loop functions (e.g.
1813 * libusb_handle_events()) then you do not need to be concerned with this
1816 * \param ctx the context to operate on, or NULL for the default context
1819 void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx) {
1820 USBI_GET_CONTEXT(ctx);
1821 usbi_mutex_lock(&ctx->event_waiters_lock);
1825 * Release the event waiters lock.
1826 * \param ctx the context to operate on, or NULL for the default context
1829 void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx) {
1830 USBI_GET_CONTEXT(ctx);
1831 usbi_mutex_unlock(&ctx->event_waiters_lock);
1835 * Wait for another thread to signal completion of an event. Must be called
1836 * with the event waiters lock held, see libusb_lock_event_waiters().
1838 * This function will block until any of the following conditions are met:
1839 * -# The timeout expires
1840 * -# A transfer completes
1841 * -# A thread releases the event handling lock through libusb_unlock_events()
1843 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1844 * the callback for the transfer has completed. Condition 3 is important
1845 * because it means that the thread that was previously handling events is no
1846 * longer doing so, so if any events are to complete, another thread needs to
1847 * step up and start event handling.
1849 * This function releases the event waiters lock before putting your thread
1850 * to sleep, and reacquires the lock as it is being woken up.
1852 * \param ctx the context to operate on, or NULL for the default context
1853 * \param tv maximum timeout for this blocking function. A NULL value
1854 * indicates unlimited timeout.
1855 * \returns 0 after a transfer completes or another thread stops event handling
1856 * \returns 1 if the timeout expired
1859 int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv) {
1861 struct timespec timeout;
1864 USBI_GET_CONTEXT(ctx);
1866 usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
1870 r = usbi_backend->clock_gettime(USBI_CLOCK_REALTIME, &timeout);
1871 if (UNLIKELY(r < 0)) {
1872 usbi_err(ctx, "failed to read realtime clock, error %d", errno);
1873 return LIBUSB_ERROR_OTHER;
1876 timeout.tv_sec += tv->tv_sec;
1877 timeout.tv_nsec += tv->tv_usec * 1000;
1878 while (timeout.tv_nsec >= 1000000000) {
1879 timeout.tv_nsec -= 1000000000;
1883 r = usbi_cond_timedwait(&ctx->event_waiters_cond,
1884 &ctx->event_waiters_lock, &timeout); // XXX crash 2014/10/02 SIGABRT/SI_TKILL
1885 return (r == ETIMEDOUT);
1888 static void handle_timeout(struct usbi_transfer *itransfer) {
1890 struct libusb_transfer *transfer =
1891 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1894 itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
1895 r = libusb_cancel_transfer(transfer);
1896 if (UNLIKELY(r < 0))
1897 usbi_warn(TRANSFER_CTX(transfer),
1898 "async cancel failed %d errno=%d", r, errno);
1901 static int handle_timeouts_locked(struct libusb_context *ctx) {
1904 struct timespec systime_ts;
1905 struct timeval systime;
1906 struct usbi_transfer *transfer;
1908 if (list_empty(&ctx->flying_transfers))
1911 /* get current time */
1912 r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
1913 if (UNLIKELY(r < 0))
1916 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
1918 /* iterate through flying transfers list, finding all transfers that
1919 * have expired timeouts */
1920 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1921 struct timeval *cur_tv = &transfer->timeout;
1923 /* if we've reached transfers of infinite timeout, we're all done */
1924 assert(cur_tv); // XXX add assert
1925 if (!timerisset(cur_tv)) // XXX crash
1928 /* ignore timeouts we've already handled */
1929 if (transfer->flags & (USBI_TRANSFER_TIMED_OUT | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
1932 /* if transfer has non-expired timeout, nothing more to do */
1933 if ((cur_tv->tv_sec > systime.tv_sec) ||
1934 (cur_tv->tv_sec == systime.tv_sec &&
1935 cur_tv->tv_usec > systime.tv_usec))
1938 /* otherwise, we've got an expired timeout to handle */
1939 handle_timeout(transfer);
1944 static int handle_timeouts(struct libusb_context *ctx) {
1947 USBI_GET_CONTEXT(ctx);
1948 usbi_mutex_lock(&ctx->flying_transfers_lock);
1950 r = handle_timeouts_locked(ctx);
1952 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1956 #ifdef USBI_TIMERFD_AVAILABLE
1957 static int handle_timerfd_trigger(struct libusb_context *ctx) {
1961 usbi_mutex_lock(&ctx->flying_transfers_lock);
1963 /* process the timeout that just happened */
1964 r = handle_timeouts_locked(ctx);
1965 if (UNLIKELY(r < 0))
1968 /* arm for next timeout*/
1969 r = arm_timerfd_for_next_timeout(ctx);
1972 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1978 /* do the actual event handling. assumes that no other thread is concurrently
1979 * doing the same thing. */
1980 static int handle_events(struct libusb_context *ctx, struct timeval *tv) {
1983 struct usbi_pollfd *ipollfd;
1984 POLL_NFDS_TYPE nfds = 0;
1985 struct pollfd *fds = NULL;
1990 usbi_mutex_lock(&ctx->pollfds_lock);
1992 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
1995 /* TODO: malloc when number of fd's changes, not on every poll */
1997 fds = malloc(sizeof(*fds) * nfds);
1998 if (UNLIKELY(!fds)) {
1999 usbi_mutex_unlock(&ctx->pollfds_lock);
2000 return LIBUSB_ERROR_NO_MEM;
2003 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd) {
2004 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
2005 int fd = pollfd->fd;
2008 fds[i].events = pollfd->events;
2012 usbi_mutex_unlock(&ctx->pollfds_lock);
2014 timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000);
2016 /* round up to next millisecond */
2017 if (tv->tv_usec % 1000)
2021 usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
2022 r = usbi_poll(fds, nfds, timeout_ms);
2023 usbi_dbg("poll() returned %d", r);
2026 return handle_timeouts(ctx);
2027 } else if (r == -1 && errno == EINTR) {
2029 return LIBUSB_ERROR_INTERRUPTED;
2030 } else if (UNLIKELY(r < 0)) {
2032 usbi_err(ctx, "poll failed %d err=%d\n", r, errno);
2033 return LIBUSB_ERROR_IO;
2038 /* fd[0] is always the ctrl pipe */
2039 if (fds[0].revents) {
2040 /* another thread wanted to interrupt event handling, and it succeeded!
2041 * handle any other events that cropped up at the same time, and
2043 usbi_dbg("caught a fish on the control pipe");
2049 /* prevent OS backend from trying to handle events on ctrl pipe */
2055 /* fd[1] is always the hotplug pipe */
2056 if (libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG) && fds[1].revents) {
2057 libusb_hotplug_message message;
2060 usbi_dbg("caught a fish on the hotplug pipe");
2063 /* read the message from the hotplug thread */
2064 ret = usbi_read(ctx->hotplug_pipe[0], &message, sizeof (message));
2065 if (ret != sizeof(message)) {
2066 usbi_err(ctx, "hotplug pipe read error %d != %u",
2067 ret, sizeof(message));
2068 r = LIBUSB_ERROR_OTHER;
2072 usbi_hotplug_match(ctx, message.device, message.event);
2074 /* the device left. dereference the device */
2075 if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == message.event)
2076 libusb_unref_device(message.device);
2081 } /* else there shouldn't be anything on this pipe */
2083 #ifdef USBI_TIMERFD_AVAILABLE
2084 /* on timerfd configurations, fds[2] is the timerfd */
2085 if (usbi_using_timerfd(ctx) && fds[2].revents) {
2086 /* timerfd indicates that a timeout has expired */
2088 usbi_dbg("timerfd triggered");
2091 ret = handle_timerfd_trigger(ctx);
2092 if (UNLIKELY(ret < 0)) {
2093 /* return error code */
2096 } else if (r == 1) {
2097 /* no more active file descriptors, nothing more to do */
2101 /* more events pending...
2102 * prevent OS backend from trying to handle events on timerfd */
2109 r = usbi_backend->handle_events(ctx, fds, nfds, r);
2111 usbi_err(ctx, "backend handle_events failed with error %d", r);
2114 if (r == 0 && special_event) {
2123 /* returns the smallest of:
2124 * 1. timeout of next URB
2125 * 2. user-supplied timeout
2126 * returns 1 if there is an already-expired timeout, otherwise returns 0
2129 static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
2130 struct timeval *out) {
2132 struct timeval timeout;
2133 int r = libusb_get_next_timeout(ctx, &timeout);
2135 /* timeout already expired? */
2136 if (!timerisset(&timeout))
2139 /* choose the smallest of next URB timeout or user specified timeout */
2140 if (timercmp(&timeout, tv, <))
2151 * Handle any pending events.
2153 * libusb determines "pending events" by checking if any timeouts have expired
2154 * and by checking the set of file descriptors for activity.
2156 * If a zero timeval is passed, this function will handle any already-pending
2157 * events and then immediately return in non-blocking style.
2159 * If a non-zero timeval is passed and no events are currently pending, this
2160 * function will block waiting for events to handle up until the specified
2161 * timeout. If an event arrives or a signal is raised, this function will
2164 * If the parameter completed is not NULL then <em>after obtaining the event
2165 * handling lock</em> this function will return immediately if the integer
2166 * pointed to is not 0. This allows for race free waiting for the completion
2167 * of a specific transfer.
2169 * \param ctx the context to operate on, or NULL for the default context
2170 * \param tv the maximum time to block waiting for events, or an all zero
2171 * timeval struct for non-blocking mode
2172 * \param completed pointer to completion integer to check, or NULL
2173 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2176 int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
2177 struct timeval *tv, int *completed) {
2180 struct timeval poll_timeout;
2182 USBI_GET_CONTEXT(ctx);
2183 r = get_next_timeout(ctx, tv, &poll_timeout);
2185 /* timeout already expired */
2186 return handle_timeouts(ctx);
2190 if (libusb_try_lock_events(ctx) == 0) {
2191 if (completed == NULL || !*completed) {
2192 /* we obtained the event lock: do our own event handling */
2193 usbi_dbg("doing our own event handling");
2194 r = handle_events(ctx, &poll_timeout);
2196 libusb_unlock_events(ctx);
2200 /* another thread is doing event handling. wait for thread events that
2201 * notify event completion. */
2202 libusb_lock_event_waiters(ctx);
2204 if (completed && *completed)
2207 if (!libusb_event_handler_active(ctx)) {
2208 /* we hit a race: whoever was event handling earlier finished in the
2209 * time it took us to reach this point. try the cycle again. */
2210 libusb_unlock_event_waiters(ctx);
2211 usbi_dbg("event handler was active but went away, retrying");
2215 usbi_dbg("another thread is doing event handling");
2216 r = libusb_wait_for_event(ctx, &poll_timeout);
2219 libusb_unlock_event_waiters(ctx);
2221 if (UNLIKELY(r < 0))
2224 return handle_timeouts(ctx);
2230 * Handle any pending events
2232 * Like libusb_handle_events_timeout_completed(), but without the completed
2233 * parameter, calling this function is equivalent to calling
2234 * libusb_handle_events_timeout_completed() with a NULL completed parameter.
2236 * This function is kept primarily for backwards compatibility.
2237 * All new code should call libusb_handle_events_completed() or
2238 * libusb_handle_events_timeout_completed() to avoid race conditions.
2240 * \param ctx the context to operate on, or NULL for the default context
2241 * \param tv the maximum time to block waiting for events, or an all zero
2242 * timeval struct for non-blocking mode
2243 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2245 int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
2246 struct timeval *tv) {
2248 return libusb_handle_events_timeout_completed(ctx, tv, NULL);
2252 * Handle any pending events in blocking mode. There is currently a timeout
2253 * hardcoded at 60 seconds but we plan to make it unlimited in future. For
2254 * finer control over whether this function is blocking or non-blocking, or
2255 * for control over the timeout, use libusb_handle_events_timeout_completed()
2258 * This function is kept primarily for backwards compatibility.
2259 * All new code should call libusb_handle_events_completed() or
2260 * libusb_handle_events_timeout_completed() to avoid race conditions.
2262 * \param ctx the context to operate on, or NULL for the default context
2263 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2265 int API_EXPORTED libusb_handle_events(libusb_context *ctx) {
2270 return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
2274 * Handle any pending events in blocking mode.
2276 * Like libusb_handle_events(), with the addition of a completed parameter
2277 * to allow for race free waiting for the completion of a specific transfer.
2279 * See libusb_handle_events_timeout_completed() for details on the completed
2282 * \param ctx the context to operate on, or NULL for the default context
2283 * \param completed pointer to completion integer to check, or NULL
2284 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2287 int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
2293 return libusb_handle_events_timeout_completed(ctx, &tv, completed);
2297 * Handle any pending events by polling file descriptors, without checking if
2298 * any other threads are already doing so. Must be called with the event lock
2299 * held, see libusb_lock_events().
2301 * This function is designed to be called under the situation where you have
2302 * taken the event lock and are calling poll()/select() directly on libusb's
2303 * file descriptors (as opposed to using libusb_handle_events() or similar).
2304 * You detect events on libusb's descriptors, so you then call this function
2305 * with a zero timeout value (while still holding the event lock).
2307 * \param ctx the context to operate on, or NULL for the default context
2308 * \param tv the maximum time to block waiting for events, or zero for
2310 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2313 int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
2314 struct timeval *tv) {
2317 struct timeval poll_timeout;
2319 USBI_GET_CONTEXT(ctx);
2320 r = get_next_timeout(ctx, tv, &poll_timeout);
2322 /* timeout already expired */
2323 return handle_timeouts(ctx);
2326 return handle_events(ctx, &poll_timeout);
2330 * Determines whether your application must apply special timing considerations
2331 * when monitoring libusb's file descriptors.
2333 * This function is only useful for applications which retrieve and poll
2334 * libusb's file descriptors in their own main loop (\ref pollmain).
2336 * Ordinarily, libusb's event handler needs to be called into at specific
2337 * moments in time (in addition to times when there is activity on the file
2338 * descriptor set). The usual approach is to use libusb_get_next_timeout()
2339 * to learn about when the next timeout occurs, and to adjust your
2340 * poll()/select() timeout accordingly so that you can make a call into the
2341 * library at that time.
2343 * Some platforms supported by libusb do not come with this baggage - any
2344 * events relevant to timing will be represented by activity on the file
2345 * descriptor set, and libusb_get_next_timeout() will always return 0.
2346 * This function allows you to detect whether you are running on such a
2351 * \param ctx the context to operate on, or NULL for the default context
2352 * \returns 0 if you must call into libusb at times determined by
2353 * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
2354 * or through regular activity on the file descriptors.
2355 * \ref pollmain "Polling libusb file descriptors for event handling"
2357 int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx) {
2359 #if defined(USBI_TIMERFD_AVAILABLE)
2360 USBI_GET_CONTEXT(ctx);
2361 return usbi_using_timerfd(ctx);
2369 * Determine the next internal timeout that libusb needs to handle. You only
2370 * need to use this function if you are calling poll() or select() or similar
2371 * on libusb's file descriptors yourself - you do not need to use it if you
2372 * are calling libusb_handle_events() or a variant directly.
2374 * You should call this function in your main loop in order to determine how
2375 * long to wait for select() or poll() to return results. libusb needs to be
2376 * called into at this timeout, so you should use it as an upper bound on
2377 * your select() or poll() call.
2379 * When the timeout has expired, call into libusb_handle_events_timeout()
2380 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
2382 * This function may return 1 (success) and an all-zero timeval. If this is
2383 * the case, it indicates that libusb has a timeout that has already expired
2384 * so you should call libusb_handle_events_timeout() or similar immediately.
2385 * A return code of 0 indicates that there are no pending timeouts.
2387 * On some platforms, this function will always returns 0 (no pending
2388 * timeouts). See \ref polltime.
2390 * \param ctx the context to operate on, or NULL for the default context
2391 * \param tv output location for a relative time against the current
2392 * clock in which libusb must be called into in order to process timeout events
2393 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
2394 * or LIBUSB_ERROR_OTHER on failure
2396 int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
2397 struct timeval *tv) {
2399 struct usbi_transfer *transfer;
2400 struct timespec cur_ts;
2401 struct timeval cur_tv;
2402 struct timeval *next_timeout;
2406 USBI_GET_CONTEXT(ctx);
2407 if (usbi_using_timerfd(ctx))
2410 usbi_mutex_lock(&ctx->flying_transfers_lock);
2412 if (list_empty(&ctx->flying_transfers)) {
2413 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2414 usbi_dbg("no URBs, no timeout!");
2418 /* find next transfer which hasn't already been processed as timed out */
2419 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2420 if (transfer->flags & (USBI_TRANSFER_TIMED_OUT | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2423 /* no timeout for this transfer? */
2424 if (!timerisset(&transfer->timeout))
2431 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2434 usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
2438 next_timeout = &transfer->timeout;
2440 r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
2441 if (UNLIKELY(r < 0)) {
2442 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2445 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
2447 if (!timercmp(&cur_tv, next_timeout, <)) {
2448 usbi_dbg("first timeout already expired");
2451 timersub(next_timeout, &cur_tv, tv);
2452 usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
2459 * Register notification functions for file descriptor additions/removals.
2460 * These functions will be invoked for every new or removed file descriptor
2461 * that libusb uses as an event source.
2463 * To remove notifiers, pass NULL values for the function pointers.
2465 * Note that file descriptors may have been added even before you register
2466 * these notifiers (e.g. at libusb_init() time).
2468 * Additionally, note that the removal notifier may be called during
2469 * libusb_exit() (e.g. when it is closing file descriptors that were opened
2470 * and added to the poll set at libusb_init() time). If you don't want this,
2471 * remove the notifiers immediately before calling libusb_exit().
2473 * \param ctx the context to operate on, or NULL for the default context
2474 * \param added_cb pointer to function for addition notifications
2475 * \param removed_cb pointer to function for removal notifications
2476 * \param user_data User data to be passed back to callbacks (useful for
2477 * passing context information)
2479 void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
2480 libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
2483 USBI_GET_CONTEXT(ctx);
2484 ctx->fd_added_cb = added_cb;
2485 ctx->fd_removed_cb = removed_cb;
2486 ctx->fd_cb_user_data = user_data;
2489 /* Add a file descriptor to the list of file descriptors to be monitored.
2490 * events should be specified as a bitmask of events passed to poll(), e.g.
2491 * POLLIN and/or POLLOUT. */
2492 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events) {
2494 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
2496 return LIBUSB_ERROR_NO_MEM;
2498 usbi_dbg("add fd %d events %d", fd, events);
2499 ipollfd->pollfd.fd = fd;
2500 ipollfd->pollfd.events = events;
2501 usbi_mutex_lock(&ctx->pollfds_lock);
2503 list_add_tail(&ipollfd->list, &ctx->pollfds);
2505 usbi_mutex_unlock(&ctx->pollfds_lock);
2507 if (ctx->fd_added_cb)
2508 ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
2512 /* Remove a file descriptor from the list of file descriptors to be polled. */
2513 void usbi_remove_pollfd(struct libusb_context *ctx, int fd) {
2515 struct usbi_pollfd *ipollfd;
2518 usbi_dbg("remove fd %d", fd);
2519 usbi_mutex_lock(&ctx->pollfds_lock);
2521 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
2522 if (ipollfd->pollfd.fd == fd) {
2528 usbi_dbg("couldn't find fd %d to remove", fd);
2529 usbi_mutex_unlock(&ctx->pollfds_lock);
2533 list_del(&ipollfd->list);
2535 usbi_mutex_unlock(&ctx->pollfds_lock);
2537 if (ctx->fd_removed_cb)
2538 ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
2542 * Retrieve a list of file descriptors that should be polled by your main loop
2543 * as libusb event sources.
2545 * The returned list is NULL-terminated and should be freed with free() when
2546 * done. The actual list contents must not be touched.
2548 * As file descriptors are a Unix-specific concept, this function is not
2549 * available on Windows and will always return NULL.
2551 * \param ctx the context to operate on, or NULL for the default context
2552 * \returns a NULL-terminated list of libusb_pollfd structures
2553 * \returns NULL on error
2554 * \returns NULL on platforms where the functionality is not available
2557 const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
2558 libusb_context *ctx) {
2561 struct libusb_pollfd **ret = NULL;
2562 struct usbi_pollfd *ipollfd;
2565 USBI_GET_CONTEXT(ctx);
2567 usbi_mutex_lock(&ctx->pollfds_lock);
2569 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
2572 ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
2576 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
2577 ret[i++] = (struct libusb_pollfd *) ipollfd;
2581 usbi_mutex_unlock(&ctx->pollfds_lock);
2582 return (const struct libusb_pollfd **) ret;
2584 usbi_err(ctx, "external polling of libusb's internal descriptors "\
2585 "is not yet supported on Windows platforms");
2590 /* Backends may call this from handle_events to report disconnection of a
2591 * device. This function ensures transfers get cancelled appropriately.
2592 * Callers of this function must hold the events_lock.
2594 void usbi_handle_disconnect(struct libusb_device_handle *handle) {
2596 struct usbi_transfer *cur;
2597 struct usbi_transfer *to_cancel;
2599 usbi_dbg("device %d.%d",
2600 handle->dev->bus_number, handle->dev->device_address);
2602 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
2605 * this is a bit tricky because:
2606 * 1. we can't do transfer completion while holding flying_transfers_lock
2607 * because the completion handler may try to re-submit the transfer
2608 * 2. the transfers list can change underneath us - if we were to build a
2609 * list of transfers to complete (while holding lock), the situation
2610 * might be different by the time we come to free them
2612 * so we resort to a loop-based approach as below
2614 * This is safe because transfers are only removed from the
2615 * flying_transfer list by usbi_handle_transfer_completion and
2616 * libusb_close, both of which hold the events_lock while doing so,
2617 * so usbi_handle_disconnect cannot be running at the same time.
2619 * Note that libusb_submit_transfer also removes the transfer from
2620 * the flying_transfer list on submission failure, but it keeps the
2621 * flying_transfer list locked between addition and removal, so
2622 * usbi_handle_disconnect never sees such transfers.
2626 usbi_mutex_lock(&HANDLE_CTX(handle)->flying_transfers_lock);
2628 list_for_each_entry(cur, &HANDLE_CTX(handle)->flying_transfers, list, struct usbi_transfer)
2629 if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
2633 usbi_mutex_unlock(&HANDLE_CTX(handle)->flying_transfers_lock);
2638 usbi_dbg("cancelling transfer %p from disconnect",
2639 USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel));
2641 usbi_backend->clear_transfer_priv(to_cancel);
2642 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);