2 * I/O functions for libusb
3 * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
4 * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
35 /* this is a list of in-flight transfer handles, sorted by timeout expiration.
36 * URBs to timeout the soonest are placed at the beginning of the list, URBs
37 * that will time out later are placed after, and urbs with infinite timeout
38 * are always placed at the very end. */
39 static struct list_head flying_transfers;
40 static pthread_mutex_t flying_transfers_lock = PTHREAD_MUTEX_INITIALIZER;
42 /* list of poll fd's */
43 static struct list_head pollfds;
44 static pthread_mutex_t pollfds_lock = PTHREAD_MUTEX_INITIALIZER;
46 /* user callbacks for pollfd changes */
47 static libusb_pollfd_added_cb fd_added_cb = NULL;
48 static libusb_pollfd_removed_cb fd_removed_cb = NULL;
50 /* this lock ensures that only one thread is handling events at any one time */
51 static pthread_mutex_t events_lock = PTHREAD_MUTEX_INITIALIZER;
53 /* used to see if there is an active thread doing event handling */
54 static int event_handler_active = 0;
56 /* used to wait for event completion in threads other than the one that is
58 static pthread_mutex_t event_waiters_lock = PTHREAD_MUTEX_INITIALIZER;
59 static pthread_cond_t event_waiters_cond = PTHREAD_COND_INITIALIZER;
62 * \page io Synchronous and asynchronous device I/O
64 * \section intro Introduction
66 * If you're using libusb in your application, you're probably wanting to
67 * perform I/O with devices - you want to perform USB data transfers.
69 * libusb offers two separate interfaces for device I/O. This page aims to
70 * introduce the two in order to help you decide which one is more suitable
71 * for your application. You can also choose to use both interfaces in your
72 * application by considering each transfer on a case-by-case basis.
74 * Once you have read through the following discussion, you should consult the
75 * detailed API documentation pages for the details:
79 * \section theory Transfers at a logical level
81 * At a logical level, USB transfers typically happen in two parts. For
82 * example, when reading data from a endpoint:
83 * -# A request for data is sent to the device
84 * -# Some time later, the incoming data is received by the host
86 * or when writing data to an endpoint:
88 * -# The data is sent to the device
89 * -# Some time later, the host receives acknowledgement from the device that
90 * the data has been transferred.
92 * There may be an indefinite delay between the two steps. Consider a
93 * fictional USB input device with a button that the user can press. In order
94 * to determine when the button is pressed, you would likely submit a request
95 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
96 * Data will arrive when the button is pressed by the user, which is
97 * potentially hours later.
99 * libusb offers both a synchronous and an asynchronous interface to performing
100 * USB transfers. The main difference is that the synchronous interface
101 * combines both steps indicated above into a single function call, whereas
102 * the asynchronous interface separates them.
104 * \section sync The synchronous interface
106 * The synchronous I/O interface allows you to perform a USB transfer with
107 * a single function call. When the function call returns, the transfer has
108 * completed and you can parse the results.
110 * If you have used the libusb-0.1 before, this I/O style will seem familar to
111 * you. libusb-0.1 only offered a synchronous interface.
113 * In our input device example, to read button presses you might write code
114 * in the following style:
116 unsigned char data[4];
118 int r = libusb_bulk_transfer(handle, EP_IN, data, sizeof(data), &actual_length, 0);
119 if (r == 0 && actual_length == sizeof(data)) {
120 // results of the transaction can now be found in the data buffer
121 // parse them here and report button press
127 * The main advantage of this model is simplicity: you did everything with
128 * a single simple function call.
130 * However, this interface has its limitations. Your application will sleep
131 * inside libusb_bulk_transfer() until the transaction has completed. If it
132 * takes the user 3 hours to press the button, your application will be
133 * sleeping for that long. Execution will be tied up inside the library -
134 * the entire thread will be useless for that duration.
136 * Another issue is that by tieing up the thread with that single transaction
137 * there is no possibility of performing I/O with multiple endpoints and/or
138 * multiple devices simultaneously, unless you resort to creating one thread
141 * Additionally, there is no opportunity to cancel the transfer after the
142 * request has been submitted.
144 * For details on how to use the synchronous API, see the
145 * \ref syncio "synchronous I/O API documentation" pages.
147 * \section async The asynchronous interface
149 * Asynchronous I/O is the most significant new feature in libusb-1.0.
150 * Although it is a more complex interface, it solves all the issues detailed
153 * Instead of providing which functions that block until the I/O has complete,
154 * libusb's asynchronous interface presents non-blocking functions which
155 * begin a transfer and then return immediately. Your application passes a
156 * callback function pointer to this non-blocking function, which libusb will
157 * call with the results of the transaction when it has completed.
159 * Transfers which have been submitted through the non-blocking functions
160 * can be cancelled with a separate function call.
162 * The non-blocking nature of this interface allows you to be simultaneously
163 * performing I/O to multiple endpoints on multiple devices, without having
166 * This added flexibility does come with some complications though:
167 * - In the interest of being a lightweight library, libusb does not create
168 * threads and can only operate when your application is calling into it. Your
169 * application must call into libusb from it's main loop when events are ready
170 * to be handled, or you must use some other scheme to allow libusb to
171 * undertake whatever work needs to be done.
172 * - libusb also needs to be called into at certain fixed points in time in
173 * order to accurately handle transfer timeouts.
174 * - Memory handling becomes more complex. You cannot use stack memory unless
175 * the function with that stack is guaranteed not to return until the transfer
176 * callback has finished executing.
177 * - You generally lose some linearity from your code flow because submitting
178 * the transfer request is done in a separate function from where the transfer
179 * results are handled. This becomes particularly obvious when you want to
180 * submit a second transfer based on the results of an earlier transfer.
182 * Internally, libusb's synchronous interface is expressed in terms of function
183 * calls to the asynchronous interface.
185 * For details on how to use the asynchronous API, see the
186 * \ref asyncio "asynchronous I/O API" documentation pages.
190 * @defgroup asyncio Asynchronous device I/O
192 * This page details libusb's asynchronous (non-blocking) API for USB device
193 * I/O. This interface is very powerful but is also quite complex - you will
194 * need to read this page carefully to understand the necessary considerations
195 * and issues surrounding use of this interface. Simplistic applications
196 * may wish to consider the \ref syncio "synchronous I/O API" instead.
198 * The asynchronous interface is built around the idea of separating transfer
199 * submission and handling of transfer completion (the synchronous model
200 * combines both of these into one). There may be a long delay between
201 * submission and completion, however the asynchronous submission function
202 * is non-blocking so will return control to your application during that
203 * potentially long delay.
205 * \section asyncabstraction Transfer abstraction
207 * For the asynchronous I/O, libusb implements the concept of a generic
208 * transfer entity for all types of I/O (control, bulk, interrupt,
209 * isochronous). The generic transfer object must be treated slightly
210 * differently depending on which type of I/O you are performing with it.
212 * This is represented by the public libusb_transfer structure type.
214 * \section asynctrf Asynchronous transfers
216 * We can view asynchronous I/O as a 5 step process:
220 * -# Completion handling
223 * \subsection asyncalloc Allocation
225 * This step involves allocating memory for a USB transfer. This is the
226 * generic transfer object mentioned above. At this stage, the transfer
227 * is "blank" with no details about what type of I/O it will be used for.
229 * Allocation is done with the libusb_alloc_transfer() function. You must use
230 * this function rather than allocating your own transfers.
232 * \subsection asyncfill Filling
234 * This step is where you take a previously allocated transfer and fill it
235 * with information to determine the message type and direction, data buffer,
236 * callback function, etc.
238 * You can either fill the required fields yourself or you can use the
239 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
240 * and libusb_fill_interrupt_transfer().
242 * \subsection asyncsubmit Submission
244 * When you have allocated a transfer and filled it, you can submit it using
245 * libusb_submit_transfer(). This function returns immediately but can be
246 * regarded as firing off the I/O request in the background.
248 * \subsection asynccomplete Completion handling
250 * After a transfer has been submitted, one of four things can happen to it:
252 * - The transfer completes (i.e. some data was transferred)
253 * - The transfer has a timeout and the timeout expires before all data is
255 * - The transfer fails due to an error
256 * - The transfer is cancelled
258 * Each of these will cause the user-specified transfer callback function to
259 * be invoked. It is up to the callback function to determine which of the
260 * above actually happened and to act accordingly.
262 * \subsection Deallocation
264 * When a transfer has completed (i.e. the callback function has been invoked),
265 * you are advised to free the transfer (unless you wish to resubmit it, see
266 * below). Transfers are deallocated with libusb_free_transfer().
268 * It is undefined behaviour to free a transfer which has not completed.
270 * \section asyncresubmit Resubmission
272 * You may be wondering why allocation, filling, and submission are all
273 * separated above where they could reasonably be combined into a single
276 * The reason for separation is to allow you to resubmit transfers without
277 * having to allocate new ones every time. This is especially useful for
278 * common situations dealing with interrupt endpoints - you allocate one
279 * transfer, fill and submit it, and when it returns with results you just
280 * resubmit it for the next interrupt.
282 * \section asynccancel Cancellation
284 * Another advantage of using the asynchronous interface is that you have
285 * the ability to cancel transfers which have not yet completed. This is
286 * done by calling the libusb_cancel_transfer() function.
288 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
289 * cancellation actually completes, the transfer's callback function will
290 * be invoked, and the callback function should check the transfer status to
291 * determine that it was cancelled.
293 * Freeing the transfer after it has been cancelled but before cancellation
294 * has completed will result in undefined behaviour.
296 * \section asyncctrl Considerations for control transfers
298 * The <tt>libusb_transfer</tt> structure is generic and hence does not
299 * include specific fields for the control-specific setup packet structure.
301 * In order to perform a control transfer, you must place the 8-byte setup
302 * packet at the start of the data buffer. To simplify this, you could
303 * cast the buffer pointer to type struct libusb_control_setup, or you can
304 * use the helper function libusb_fill_control_setup().
306 * The wLength field placed in the setup packet must be the length you would
307 * expect to be sent in the setup packet: the length of the payload that
308 * follows (or the expected maximum number of bytes to receive). However,
309 * the length field of the libusb_transfer object must be the length of
310 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
311 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
313 * If you use the helper functions, this is simplified for you:
314 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
315 * data you are sending/requesting.
316 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
317 * request size as the wLength value (i.e. do not include the extra space you
318 * allocated for the control setup).
319 * -# If this is a host-to-device transfer, place the data to be transferred
320 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
321 * -# Call libusb_fill_control_transfer() to associate the data buffer with
322 * the transfer (and to set the remaining details such as callback and timeout).
323 * - Note that there is no parameter to set the length field of the transfer.
324 * The length is automatically inferred from the wLength field of the setup
326 * -# Submit the transfer.
328 * The multi-byte control setup fields (wValue, wIndex and wLength) must
329 * be given in little-endian byte order (the endianness of the USB bus).
330 * Endianness conversion is transparently handled by
331 * libusb_fill_control_setup() which is documented to accept host-endian
334 * Further considerations are needed when handling transfer completion in
335 * your callback function:
336 * - As you might expect, the setup packet will still be sitting at the start
337 * of the data buffer.
338 * - If this was a device-to-host transfer, the received data will be sitting
339 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
340 * - The actual_length field of the transfer structure is relative to the
341 * wLength of the setup packet, rather than the size of the data buffer. So,
342 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
343 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
344 * transferred in entirity.
346 * To simplify parsing of setup packets and obtaining the data from the
347 * correct offset, you may wish to use the libusb_control_transfer_get_data()
348 * and libusb_control_transfer_get_setup() functions within your transfer
351 * Even though control endpoints do not halt, a completed control transfer
352 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
353 * request was not supported.
355 * \section asyncintr Considerations for interrupt transfers
357 * All interrupt transfers are performed using the polling interval presented
358 * by the bInterval value of the endpoint descriptor.
360 * \section asynciso Considerations for isochronous transfers
362 * Isochronous transfers are more complicated than transfers to
363 * non-isochronous endpoints.
365 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
366 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
368 * During filling, set \ref libusb_transfer::type "type" to
369 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
370 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
371 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
372 * or equal to the number of packets you requested during allocation.
373 * libusb_alloc_transfer() does not set either of these fields for you, given
374 * that you might not even use the transfer on an isochronous endpoint.
376 * Next, populate the length field for the first num_iso_packets entries in
377 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
378 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
379 * packet length is determined by wMaxPacketSize field in the endpoint
380 * descriptor. Two functions can help you here:
382 * - libusb_get_max_packet_size() is an easy way to determine the max
383 * packet size for an endpoint.
384 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
385 * within a transfer, which is usually what you want.
387 * For outgoing transfers, you'll obviously fill the buffer and populate the
388 * packet descriptors in hope that all the data gets transferred. For incoming
389 * transfers, you must ensure the buffer has sufficient capacity for
390 * the situation where all packets transfer the full amount of requested data.
392 * Completion handling requires some extra consideration. The
393 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
394 * is meaningless and should not be examined; instead you must refer to the
395 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
396 * each individual packet.
398 * The \ref libusb_transfer::status "status" field of the transfer is also a
400 * - If the packets were submitted and the isochronous data microframes
401 * completed normally, status will have value
402 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
403 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
404 * delays are not counted as transfer errors; the transfer.status field may
405 * indicate COMPLETED even if some or all of the packets failed. Refer to
406 * the \ref libusb_iso_packet_descriptor::status "status" field of each
407 * individual packet to determine packet failures.
408 * - The status field will have value
409 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
410 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
411 * - Other transfer status codes occur with normal behaviour.
413 * The data for each packet will be found at an offset into the buffer that
414 * can be calculated as if each prior packet completed in full. The
415 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
416 * functions may help you here.
418 * \section asyncmem Memory caveats
420 * In most circumstances, it is not safe to use stack memory for transfer
421 * buffers. This is because the function that fired off the asynchronous
422 * transfer may return before libusb has finished using the buffer, and when
423 * the function returns it's stack gets destroyed. This is true for both
424 * host-to-device and device-to-host transfers.
426 * The only case in which it is safe to use stack memory is where you can
427 * guarantee that the function owning the stack space for the buffer does not
428 * return until after the transfer's callback function has completed. In every
429 * other case, you need to use heap memory instead.
431 * \section asyncflags Fine control
433 * Through using this asynchronous interface, you may find yourself repeating
434 * a few simple operations many times. You can apply a bitwise OR of certain
435 * flags to a transfer to simplify certain things:
436 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
437 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
438 * less than the requested amount of data being marked with status
439 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
440 * (they would normally be regarded as COMPLETED)
441 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
442 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
443 * buffer when freeing the transfer.
444 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
445 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
446 * transfer after the transfer callback returns.
448 * \section asyncevent Event handling
450 * In accordance of the aim of being a lightweight library, libusb does not
451 * create threads internally. This means that libusb code does not execute
452 * at any time other than when your application is calling a libusb function.
453 * However, an asynchronous model requires that libusb perform work at various
454 * points in time - namely processing the results of previously-submitted
455 * transfers and invoking the user-supplied callback function.
457 * This gives rise to the libusb_handle_events() function which your
458 * application must call into when libusb has work do to. This gives libusb
459 * the opportunity to reap pending transfers, invoke callbacks, etc.
461 * The first issue to discuss here is how your application can figure out
462 * when libusb has work to do. In fact, there are two naive options which
463 * do not actually require your application to know this:
464 * -# Periodically call libusb_handle_events() in non-blocking mode at fixed
465 * short intervals from your main loop
466 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
469 * The first option is plainly not very nice, and will cause unnecessary
470 * CPU wakeups leading to increased power usage and decreased battery life.
471 * The second option is not very nice either, but may be the nicest option
472 * available to you if the "proper" approach can not be applied to your
473 * application (read on...).
475 * The recommended option is to integrate libusb with your application main
476 * event loop. libusb exposes a set of file descriptors which allow you to do
477 * this. Your main loop is probably already calling poll() or select() or a
478 * variant on a set of file descriptors for other event sources (e.g. keyboard
479 * button presses, mouse movements, network sockets, etc). You then add
480 * libusb's file descriptors to your poll()/select() calls, and when activity
481 * is detected on such descriptors you know it is time to call
482 * libusb_handle_events().
484 * There is one final event handling complication. libusb supports
485 * asynchronous transfers which time out after a specified time period, and
486 * this requires that libusb is called into at or after the timeout so that
487 * the timeout can be handled. So, in addition to considering libusb's file
488 * descriptors in your main event loop, you must also consider that libusb
489 * sometimes needs to be called into at fixed points in time even when there
490 * is no file descriptor activity.
492 * For the details on retrieving the set of file descriptors and determining
493 * the next timeout, see the \ref poll "polling and timing" API documentation.
497 * @defgroup poll Polling and timing
499 * This page documents libusb's functions for polling events and timing.
500 * These functions are only necessary for users of the
501 * \ref asyncio "asynchronous API". If you are only using the simpler
502 * \ref syncio "synchronous API" then you do not need to ever call these
505 * The justification for the functionality described here has already been
506 * discussed in the \ref asyncevent "event handling" section of the
507 * asynchronous API documentation. In summary, libusb does not create internal
508 * threads for event processing and hence relies on your application calling
509 * into libusb at certain points in time so that pending events can be handled.
510 * In order to know precisely when libusb needs to be called into, libusb
511 * offers you a set of pollable file descriptors and information about when
512 * the next timeout expires.
514 * If you are using the asynchronous I/O API, you must take one of the two
515 * following options, otherwise your I/O will not complete.
517 * \section pollsimple The simple option
519 * If your application revolves solely around libusb and does not need to
520 * handle other event sources, you can have a program structure as follows:
523 // find and open device
524 // maybe fire off some initial async I/O
526 while (user_has_not_requested_exit)
527 libusb_handle_events();
532 * With such a simple main loop, you do not have to worry about managing
533 * sets of file descriptors or handling timeouts. libusb_handle_events() will
534 * handle those details internally.
536 * \section pollmain The more advanced option
538 * In more advanced applications, you will already have a main loop which
539 * is monitoring other event sources: network sockets, X11 events, mouse
540 * movements, etc. Through exposing a set of file descriptors, libusb is
541 * designed to cleanly integrate into such main loops.
543 * In addition to polling file descriptors for the other event sources, you
544 * take a set of file descriptors from libusb and monitor those too. When you
545 * detect activity on libusb's file descriptors, you call
546 * libusb_handle_events_timeout() in non-blocking mode.
548 * You must also consider the fact that libusb sometimes has to handle events
549 * at certain known times which do not generate activity on file descriptors.
550 * Your main loop must also consider these times, modify it's poll()/select()
551 * timeout accordingly, and track time so that libusb_handle_events_timeout()
552 * is called in non-blocking mode when timeouts expire.
554 * In pseudo-code, you want something that looks like:
559 while (user has not requested application exit) {
560 libusb_get_next_timeout();
561 select(on libusb file descriptors plus any other event sources of interest,
562 using a timeout no larger than the value libusb just suggested)
563 if (select() indicated activity on libusb file descriptors)
564 libusb_handle_events_timeout(0);
565 if (time has elapsed to or beyond the libusb timeout)
566 libusb_handle_events_timeout(0);
572 * The set of file descriptors that libusb uses as event sources may change
573 * during the life of your application. Rather than having to repeatedly
574 * call libusb_get_pollfds(), you can set up notification functions for when
575 * the file descriptor set changes using libusb_set_pollfd_notifiers().
577 * \section mtissues Multi-threaded considerations
579 * Unfortunately, the situation is complicated further when multiple threads
580 * come into play. If two threads are monitoring the same file descriptors,
581 * the fact that only one thread will be woken up when an event occurs causes
584 * The events lock, event waiters lock, and libusb_handle_events_locked()
585 * entities are added to solve these problems. You do not need to be concerned
586 * with these entities otherwise.
588 * See the extra documentation: \ref mtasync
591 /** \page mtasync Multi-threaded applications and asynchronous I/O
593 * libusb is a thread-safe library, but extra considerations must be applied
594 * to applications which interact with libusb from multiple threads.
596 * The underlying issue that must be addressed is that all libusb I/O
597 * revolves around monitoring file descriptors through the poll()/select()
598 * system calls. This is directly exposed at the
599 * \ref asyncio "asynchronous interface" but it is important to note that the
600 * \ref syncio "synchronous interface" is implemented on top of the
601 * asynchonrous interface, therefore the same considerations apply.
603 * The issue is that if two or more threads are concurrently calling poll()
604 * or select() on libusb's file descriptors then only one of those threads
605 * will be woken up when an event arrives. The others will be completely
606 * oblivious that anything has happened.
608 * Consider the following pseudo-code, which submits an asynchronous transfer
609 * then waits for its completion. This style is one way you could implement a
610 * synchronous interface on top of the asynchronous interface (and libusb
611 * does something similar, albeit more advanced due to the complications
612 * explained on this page).
615 void cb(struct libusb_transfer *transfer)
617 int *completed = transfer->user_data;
622 const struct timeval timeout = { 120, 0 };
623 struct libusb_transfer *transfer;
624 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE];
627 transfer = libusb_alloc_transfer(0);
628 libusb_fill_control_setup(buffer,
629 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
630 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
631 libusb_submit_transfer(transfer);
634 poll(libusb file descriptors, 120*1000);
635 if (poll indicates activity)
636 libusb_handle_events_timeout(0);
638 printf("completed!");
643 * Here we are <em>serializing</em> completion of an asynchronous event
644 * against a condition - the condition being completion of a specific transfer.
645 * The poll() loop has a long timeout to minimize CPU usage during situations
646 * when nothing is happening (it could reasonably be unlimited).
648 * If this is the only thread that is polling libusb's file descriptors, there
649 * is no problem: there is no danger that another thread will swallow up the
650 * event that we are interested in. On the other hand, if there is another
651 * thread polling the same descriptors, there is a chance that it will receive
652 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
653 * will only realise that the transfer has completed on the next iteration of
654 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
655 * undesirable, and don't even think about using short timeouts to circumvent
658 * The solution here is to ensure that no two threads are ever polling the
659 * file descriptors at the same time. A naive implementation of this would
660 * impact the capabilities of the library, so libusb offers the scheme
661 * documented below to ensure no loss of functionality.
663 * Before we go any further, it is worth mentioning that all libusb-wrapped
664 * event handling procedures fully adhere to the scheme documented below.
665 * This includes libusb_handle_events() and all the synchronous I/O functions -
666 * libusb hides this headache from you. You do not need to worry about any
667 * of these issues if you stick to that level.
669 * The problem is when we consider the fact that libusb exposes file
670 * descriptors to allow for you to integrate asynchronous USB I/O into
671 * existing main loops, effectively allowing you to do some work behind
672 * libusb's back. If you do take libusb's file descriptors and pass them to
673 * poll()/select() yourself, you need to be aware of the associated issues.
675 * \section eventlock The events lock
677 * The first concept to be introduced is the events lock. The events lock
678 * is used to serialize threads that want to handle events, such that only
679 * one thread is handling events at any one time.
681 * You must take the events lock before polling libusb file descriptors,
682 * using libusb_lock_events(). You must release the lock as soon as you have
683 * aborted your poll()/select() loop, using libusb_unlock_events().
685 * \section threadwait Letting other threads do the work for you
687 * Although the events lock is a critical part of the solution, it is not
688 * enough on it's own. You might wonder if the following is sufficient...
690 libusb_lock_events();
692 poll(libusb file descriptors, 120*1000);
693 if (poll indicates activity)
694 libusb_handle_events_timeout(0);
696 libusb_lock_events();
698 * ...and the answer is that it is not. This is because the transfer in the
699 * code shown above may take a long time (say 30 seconds) to complete, and
700 * the lock is not released until the transfer is completed.
702 * Another thread with similar code that wants to do event handling may be
703 * working with a transfer that completes after a few milliseconds. Despite
704 * having such a quick completion time, the other thread cannot check that
705 * status of its transfer until the code above has finished (30 seconds later)
706 * due to contention on the lock.
708 * To solve this, libusb offers you a mechanism to determine when another
709 * thread is handling events. It also offers a mechanism to block your thread
710 * until the event handling thread has completed an event (and this mechanism
711 * does not involve polling of file descriptors).
713 * After determining that another thread is currently handling events, you
714 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
715 * You then re-check that some other thread is still handling events, and if
716 * so, you call libusb_wait_for_event().
718 * libusb_wait_for_event() puts your application to sleep until an event
719 * occurs, or until a thread releases the events lock. When either of these
720 * things happen, your thread is woken up, and should re-check the condition
721 * it was waiting on. It should also re-check that another thread is handling
722 * events, and if not, it should start handling events itself.
724 * This looks like the following, as pseudo-code:
727 if (libusb_try_lock_events() == 0) {
728 // we obtained the event lock: do our own event handling
729 libusb_lock_events();
731 poll(libusb file descriptors, 120*1000);
732 if (poll indicates activity)
733 libusb_handle_events_locked(0);
735 libusb_unlock_events();
737 // another thread is doing event handling. wait for it to signal us that
738 // an event has completed
739 libusb_lock_event_waiters();
742 // now that we have the event waiters lock, double check that another
743 // thread is still handling events for us. (it may have ceased handling
744 // events in the time it took us to reach this point)
745 if (!libusb_event_handler_active()) {
746 // whoever was handling events is no longer doing so, try again
747 libusb_unlock_event_waiters();
751 libusb_wait_for_event();
753 libusb_unlock_event_waiters();
755 printf("completed!\n");
758 * We have now implemented code which can dynamically handle situations where
759 * nobody is handling events (so we should do it ourselves), and it can also
760 * handle situations where another thread is doing event handling (so we can
761 * piggyback onto them). It is also equipped to handle a combination of
762 * the two, for example, another thread is doing event handling, but for
763 * whatever reason it stops doing so before our condition is met, so we take
764 * over the event handling.
766 * Three functions were introduced in the above pseudo-code. Their importance
767 * should be apparent from the code shown above.
768 * -# libusb_try_lock_events() is a non-blocking function which attempts
769 * to acquire the events lock but returns a failure code if it is contended.
770 * -# libusb_handle_events_locked() is a variant of
771 * libusb_handle_events_timeout() that you can call while holding the
772 * events lock. libusb_handle_events_timeout() itself implements similar
773 * logic to the above, so be sure not to call it when you are
774 * "working behind libusb's back", as is the case here.
775 * -# libusb_event_handler_active() determines if someone is currently
776 * holding the events lock
778 * You might be wondering why there is no function to wake up all threads
779 * blocked on libusb_wait_for_event(). This is because libusb can do this
780 * internally: it will wake up all such threads when someone calls
781 * libusb_unlock_events() or when a transfer completes (at the point after its
782 * callback has returned).
784 * \subsection concl Closing remarks
786 * The above may seem a little complicated, but hopefully I have made it clear
787 * why such complications are necessary. Also, do not forget that this only
788 * applies to applications that take libusb's file descriptors and integrate
789 * them into their own polling loops.
791 * You may decide that it is OK for your multi-threaded application to ignore
792 * some of the rules and locks detailed above, because you don't think that
793 * two threads can ever be polling the descriptors at the same time. If that
794 * is the case, then that's good news for you because you don't have to worry.
795 * But be careful here; remember that the synchronous I/O functions do event
796 * handling internally. If you have one thread doing event handling in a loop
797 * (without implementing the rules and locking semantics documented above)
798 * and another trying to send a synchronous USB transfer, you will end up with
799 * two threads monitoring the same descriptors, and the above-described
800 * undesirable behaviour occuring. The solution is for your polling thread to
801 * play by the rules; the synchronous I/O functions do so, and this will result
802 * in them getting along in perfect harmony.
804 * If you do have a dedicated thread doing event handling, it is perfectly
805 * legal for it to take the event handling lock and never release it. Any
806 * synchronous I/O functions you call from other threads will transparently
807 * fall back to the "event waiters" mechanism detailed above.
812 list_init(&flying_transfers);
815 fd_removed_cb = NULL;
818 static int calculate_timeout(struct usbi_transfer *transfer)
821 struct timespec current_time;
822 unsigned int timeout =
823 __USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
828 r = clock_gettime(CLOCK_MONOTONIC, ¤t_time);
830 usbi_err("failed to read monotonic clock, errno=%d", errno);
834 current_time.tv_sec += timeout / 1000;
835 current_time.tv_nsec += (timeout % 1000) * 1000000;
837 if (current_time.tv_nsec > 1000000000) {
838 current_time.tv_nsec -= 1000000000;
839 current_time.tv_sec++;
842 TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
846 static void add_to_flying_list(struct usbi_transfer *transfer)
848 struct usbi_transfer *cur;
849 struct timeval *timeout = &transfer->timeout;
851 pthread_mutex_lock(&flying_transfers_lock);
853 /* if we have no other flying transfers, start the list with this one */
854 if (list_empty(&flying_transfers)) {
855 list_add(&transfer->list, &flying_transfers);
859 /* if we have infinite timeout, append to end of list */
860 if (!timerisset(timeout)) {
861 list_add_tail(&transfer->list, &flying_transfers);
865 /* otherwise, find appropriate place in list */
866 list_for_each_entry(cur, &flying_transfers, list) {
867 /* find first timeout that occurs after the transfer in question */
868 struct timeval *cur_tv = &cur->timeout;
870 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
871 (cur_tv->tv_sec == timeout->tv_sec &&
872 cur_tv->tv_usec > timeout->tv_usec)) {
873 list_add_tail(&transfer->list, &cur->list);
878 /* otherwise we need to be inserted at the end */
879 list_add_tail(&transfer->list, &flying_transfers);
881 pthread_mutex_unlock(&flying_transfers_lock);
885 * Allocate a libusb transfer with a specified number of isochronous packet
886 * descriptors. The returned transfer is pre-initialized for you. When the new
887 * transfer is no longer needed, it should be freed with
888 * libusb_free_transfer().
890 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
891 * interrupt) should specify an iso_packets count of zero.
893 * For transfers intended for isochronous endpoints, specify an appropriate
894 * number of packet descriptors to be allocated as part of the transfer.
895 * The returned transfer is not specially initialized for isochronous I/O;
896 * you are still required to set the
897 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
898 * \ref libusb_transfer::type "type" fields accordingly.
900 * It is safe to allocate a transfer with some isochronous packets and then
901 * use it on a non-isochronous endpoint. If you do this, ensure that at time
902 * of submission, num_iso_packets is 0 and that type is set appropriately.
904 * \param iso_packets number of isochronous packet descriptors to allocate
905 * \returns a newly allocated transfer, or NULL on error
907 API_EXPORTED struct libusb_transfer *libusb_alloc_transfer(int iso_packets)
909 size_t os_alloc_size = usbi_backend->transfer_priv_size
910 + (usbi_backend->add_iso_packet_size * iso_packets);
911 int alloc_size = sizeof(struct usbi_transfer)
912 + sizeof(struct libusb_transfer)
913 + (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
915 struct usbi_transfer *itransfer = malloc(alloc_size);
919 memset(itransfer, 0, alloc_size);
920 itransfer->num_iso_packets = iso_packets;
921 return __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
925 * Free a transfer structure. This should be called for all transfers
926 * allocated with libusb_alloc_transfer().
928 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
929 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
930 * non-NULL, this function will also free the transfer buffer using the
931 * standard system memory allocator (e.g. free()).
933 * It is legal to call this function with a NULL transfer. In this case,
934 * the function will simply return safely.
936 * \param transfer the transfer to free
938 API_EXPORTED void libusb_free_transfer(struct libusb_transfer *transfer)
940 struct usbi_transfer *itransfer;
944 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
945 free(transfer->buffer);
947 itransfer = __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
952 * Submit a transfer. This function will fire off the USB transfer and then
953 * return immediately.
955 * It is undefined behaviour to submit a transfer that has already been
956 * submitted but has not yet completed.
958 * \param transfer the transfer to submit
959 * \returns 0 on success
960 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
961 * \returns another LIBUSB_ERROR code on other failure
963 API_EXPORTED int libusb_submit_transfer(struct libusb_transfer *transfer)
965 struct usbi_transfer *itransfer =
966 __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
969 itransfer->transferred = 0;
970 r = calculate_timeout(itransfer);
972 return LIBUSB_ERROR_OTHER;
974 add_to_flying_list(itransfer);
975 r = usbi_backend->submit_transfer(itransfer);
977 pthread_mutex_lock(&flying_transfers_lock);
978 list_del(&itransfer->list);
979 pthread_mutex_unlock(&flying_transfers_lock);
986 * Asynchronously cancel a previously submitted transfer.
987 * It is undefined behaviour to call this function on a transfer that is
988 * already being cancelled or has already completed.
989 * This function returns immediately, but this does not indicate cancellation
990 * is complete. Your callback function will be invoked at some later time
991 * with a transfer status of
992 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
993 * "LIBUSB_TRANSFER_CANCELLED."
995 * \param transfer the transfer to cancel
996 * \returns 0 on success
997 * \returns a LIBUSB_ERROR code on failure
999 API_EXPORTED int libusb_cancel_transfer(struct libusb_transfer *transfer)
1001 struct usbi_transfer *itransfer =
1002 __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1006 r = usbi_backend->cancel_transfer(itransfer);
1008 usbi_err("cancel transfer failed error %d", r);
1012 /* Handle completion of a transfer (completion might be an error condition).
1013 * This will invoke the user-supplied callback function, which may end up
1014 * freeing the transfer. Therefore you cannot use the transfer structure
1015 * after calling this function, and you should free all backend-specific
1016 * data before calling it. */
1017 void usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1018 enum libusb_transfer_status status)
1020 struct libusb_transfer *transfer =
1021 __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1024 pthread_mutex_lock(&flying_transfers_lock);
1025 list_del(&itransfer->list);
1026 pthread_mutex_unlock(&flying_transfers_lock);
1028 if (status == LIBUSB_TRANSFER_COMPLETED
1029 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1030 int rqlen = transfer->length;
1031 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1032 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1033 if (rqlen != itransfer->transferred) {
1034 usbi_dbg("interpreting short transfer as error");
1035 status = LIBUSB_TRANSFER_ERROR;
1039 flags = transfer->flags;
1040 transfer->status = status;
1041 transfer->actual_length = itransfer->transferred;
1042 if (transfer->callback)
1043 transfer->callback(transfer);
1044 /* transfer might have been freed by the above call, do not use from
1046 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1047 libusb_free_transfer(transfer);
1048 pthread_mutex_lock(&event_waiters_lock);
1049 pthread_cond_broadcast(&event_waiters_cond);
1050 pthread_mutex_unlock(&event_waiters_lock);
1053 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1054 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1055 * transfers exist here.
1057 void usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
1059 /* if the URB was cancelled due to timeout, report timeout to the user */
1060 if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
1061 usbi_dbg("detected timeout cancellation");
1062 usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
1066 /* otherwise its a normal async cancel */
1067 usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
1071 * Attempt to acquire the event handling lock. This lock is used to ensure that
1072 * only one thread is monitoring libusb event sources at any one time.
1074 * You only need to use this lock if you are developing an application
1075 * which calls poll() or select() on libusb's file descriptors directly.
1076 * If you stick to libusb's event handling loop functions (e.g.
1077 * libusb_handle_events()) then you do not need to be concerned with this
1080 * While holding this lock, you are trusted to actually be handling events.
1081 * If you are no longer handling events, you must call libusb_unlock_events()
1082 * as soon as possible.
1084 * \returns 0 if the lock was obtained successfully
1085 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1088 API_EXPORTED int libusb_try_lock_events(void)
1090 int r = pthread_mutex_trylock(&events_lock);
1094 event_handler_active = 1;
1099 * Acquire the event handling lock, blocking until successful acquisition if
1100 * it is contended. This lock is used to ensure that only one thread is
1101 * monitoring libusb event sources at any one time.
1103 * You only need to use this lock if you are developing an application
1104 * which calls poll() or select() on libusb's file descriptors directly.
1105 * If you stick to libusb's event handling loop functions (e.g.
1106 * libusb_handle_events()) then you do not need to be concerned with this
1109 * While holding this lock, you are trusted to actually be handling events.
1110 * If you are no longer handling events, you must call libusb_unlock_events()
1111 * as soon as possible.
1115 API_EXPORTED void libusb_lock_events(void)
1117 pthread_mutex_lock(&events_lock);
1118 event_handler_active = 1;
1122 * Release the lock previously acquired with libusb_try_lock_events() or
1123 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1124 * on libusb_wait_for_event().
1128 API_EXPORTED void libusb_unlock_events(void)
1130 event_handler_active = 0;
1131 pthread_mutex_unlock(&events_lock);
1133 pthread_mutex_lock(&event_waiters_lock);
1134 pthread_cond_broadcast(&event_waiters_cond);
1135 pthread_mutex_unlock(&event_waiters_lock);
1139 * Determine if an active thread is handling events (i.e. if anyone is holding
1140 * the event handling lock).
1142 * \returns 1 if a thread is handling events
1143 * \returns 0 if there are no threads currently handling events
1146 API_EXPORTED int libusb_event_handler_active(void)
1148 return event_handler_active;
1152 * Acquire the event waiters lock. This lock is designed to be obtained under
1153 * the situation where you want to be aware when events are completed, but
1154 * some other thread is event handling so calling libusb_handle_events() is not
1157 * You then obtain this lock, re-check that another thread is still handling
1158 * events, then call libusb_wait_for_event().
1160 * You only need to use this lock if you are developing an application
1161 * which calls poll() or select() on libusb's file descriptors directly,
1162 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1163 * If you stick to libusb's event handling loop functions (e.g.
1164 * libusb_handle_events()) then you do not need to be concerned with this
1169 API_EXPORTED void libusb_lock_event_waiters(void)
1171 pthread_mutex_lock(&event_waiters_lock);
1175 * Release the event waiters lock.
1178 API_EXPORTED void libusb_unlock_event_waiters(void)
1180 pthread_mutex_unlock(&event_waiters_lock);
1184 * Wait for another thread to signal completion of an event. Must be called
1185 * with the event waiters lock held, see libusb_lock_event_waiters().
1187 * This function will block until any of the following conditions are met:
1188 * -# The timeout expires
1189 * -# A transfer completes
1190 * -# A thread releases the event handling lock through libusb_unlock_events()
1192 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1193 * the callback for the transfer has completed. Condition 3 is important
1194 * because it means that the thread that was previously handling events is no
1195 * longer doing so, so if any events are to complete, another thread needs to
1196 * step up and start event handling.
1198 * This function releases the event waiters lock before putting your thread
1199 * to sleep, and reacquires the lock as it is being woken up.
1201 * \param tv maximum timeout for this blocking function. A NULL value
1202 * indicates unlimited timeout.
1203 * \returns 0 after a transfer completes or another thread stops event handling
1204 * \returns 1 if the timeout expired
1207 API_EXPORTED int libusb_wait_for_event(struct timeval *tv)
1209 struct timespec timeout;
1213 pthread_cond_wait(&event_waiters_cond, &event_waiters_lock);
1217 r = clock_gettime(CLOCK_REALTIME, &timeout);
1219 usbi_err("failed to read realtime clock, error %d", errno);
1220 return LIBUSB_ERROR_OTHER;
1223 timeout.tv_sec += tv->tv_sec;
1224 timeout.tv_nsec += tv->tv_usec * 1000;
1225 if (timeout.tv_nsec > 1000000000) {
1226 timeout.tv_nsec -= 1000000000;
1230 r = pthread_cond_timedwait(&event_waiters_cond, &event_waiters_lock,
1232 return (r == ETIMEDOUT);
1235 static void handle_timeout(struct usbi_transfer *itransfer)
1237 struct libusb_transfer *transfer =
1238 __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1241 itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
1242 r = libusb_cancel_transfer(transfer);
1244 usbi_warn("async cancel failed %d errno=%d", r, errno);
1247 static int handle_timeouts(void)
1249 struct timespec systime_ts;
1250 struct timeval systime;
1251 struct usbi_transfer *transfer;
1254 pthread_mutex_lock(&flying_transfers_lock);
1255 if (list_empty(&flying_transfers))
1258 /* get current time */
1259 r = clock_gettime(CLOCK_MONOTONIC, &systime_ts);
1263 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
1265 /* iterate through flying transfers list, finding all transfers that
1266 * have expired timeouts */
1267 list_for_each_entry(transfer, &flying_transfers, list) {
1268 struct timeval *cur_tv = &transfer->timeout;
1270 /* if we've reached transfers of infinite timeout, we're all done */
1271 if (!timerisset(cur_tv))
1274 /* ignore timeouts we've already handled */
1275 if (transfer->flags & USBI_TRANSFER_TIMED_OUT)
1278 /* if transfer has non-expired timeout, nothing more to do */
1279 if ((cur_tv->tv_sec > systime.tv_sec) ||
1280 (cur_tv->tv_sec == systime.tv_sec &&
1281 cur_tv->tv_usec > systime.tv_usec))
1284 /* otherwise, we've got an expired timeout to handle */
1285 handle_timeout(transfer);
1289 pthread_mutex_unlock(&flying_transfers_lock);
1293 /* do the actual event handling. assumes that no other thread is concurrently
1294 * doing the same thing. */
1295 static int handle_events(struct timeval *tv)
1298 struct usbi_pollfd *ipollfd;
1304 pthread_mutex_lock(&pollfds_lock);
1305 list_for_each_entry(ipollfd, &pollfds, list)
1308 /* TODO: malloc when number of fd's changes, not on every poll */
1309 fds = malloc(sizeof(*fds) * nfds);
1311 return LIBUSB_ERROR_NO_MEM;
1313 list_for_each_entry(ipollfd, &pollfds, list) {
1314 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
1315 int fd = pollfd->fd;
1318 fds[i].events = pollfd->events;
1321 pthread_mutex_unlock(&pollfds_lock);
1323 timeout_ms = (tv->tv_sec * 1000) + (tv->tv_usec / 1000);
1324 usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
1325 r = poll(fds, nfds, timeout_ms);
1326 usbi_dbg("poll() returned %d", r);
1329 return handle_timeouts();
1330 } else if (r == -1 && errno == EINTR) {
1332 return LIBUSB_ERROR_INTERRUPTED;
1335 usbi_err("poll failed %d err=%d\n", r, errno);
1336 return LIBUSB_ERROR_IO;
1339 r = usbi_backend->handle_events(fds, nfds, r);
1341 usbi_err("backend handle_events failed with error %d", r);
1347 /* returns the smallest of:
1348 * 1. timeout of next URB
1349 * 2. user-supplied timeout
1350 * returns 1 if there is an already-expired timeout, otherwise returns 0
1353 static int get_next_timeout(struct timeval *tv, struct timeval *out)
1355 struct timeval timeout;
1356 int r = libusb_get_next_timeout(&timeout);
1358 /* timeout already expired? */
1359 if (!timerisset(&timeout))
1362 /* choose the smallest of next URB timeout or user specified timeout */
1363 if (timercmp(&timeout, tv, <))
1374 * Handle any pending events.
1376 * libusb determines "pending events" by checking if any timeouts have expired
1377 * and by checking the set of file descriptors for activity.
1379 * If a zero timeval is passed, this function will handle any already-pending
1380 * events and then immediately return in non-blocking style.
1382 * If a non-zero timeval is passed and no events are currently pending, this
1383 * function will block waiting for events to handle up until the specified
1384 * timeout. If an event arrives or a signal is raised, this function will
1387 * \param tv the maximum time to block waiting for events, or zero for
1389 * \returns 0 on success, or a LIBUSB_ERROR code on failure
1391 API_EXPORTED int libusb_handle_events_timeout(struct timeval *tv)
1394 struct timeval poll_timeout;
1396 r = get_next_timeout(tv, &poll_timeout);
1398 /* timeout already expired */
1399 return handle_timeouts();
1403 if (libusb_try_lock_events() == 0) {
1404 /* we obtained the event lock: do our own event handling */
1405 r = handle_events(&poll_timeout);
1406 libusb_unlock_events();
1410 /* another thread is doing event handling. wait for pthread events that
1411 * notify event completion. */
1412 libusb_lock_event_waiters();
1414 if (!libusb_event_handler_active()) {
1415 /* we hit a race: whoever was event handling earlier finished in the
1416 * time it took us to reach this point. try the cycle again. */
1417 libusb_unlock_event_waiters();
1418 usbi_dbg("event handler was active but went away, retrying");
1422 usbi_dbg("another thread is doing event handling");
1423 r = libusb_wait_for_event(&poll_timeout);
1424 libusb_unlock_event_waiters();
1429 return handle_timeouts();
1435 * Handle any pending events in blocking mode with a sensible timeout. This
1436 * timeout is currently hardcoded at 2 seconds but we may change this if we
1437 * decide other values are more sensible. For finer control over whether this
1438 * function is blocking or non-blocking, or the maximum timeout, use
1439 * libusb_handle_events_timeout() instead.
1441 * \returns 0 on success, or a LIBUSB_ERROR code on failure
1443 API_EXPORTED int libusb_handle_events(void)
1448 return libusb_handle_events_timeout(&tv);
1452 * Handle any pending events by polling file descriptors, without checking if
1453 * any other threads are already doing so. Must be called with the event lock
1454 * held, see libusb_lock_events().
1456 * This function is designed to be called under the situation where you have
1457 * taken the event lock and are calling poll()/select() directly on libusb's
1458 * file descriptors (as opposed to using libusb_handle_events() or similar).
1459 * You detect events on libusb's descriptors, so you then call this function
1460 * with a zero timeout value (while still holding the event lock).
1462 * \param tv the maximum time to block waiting for events, or zero for
1464 * \returns 0 on success, or a LIBUSB_ERROR code on failure
1467 API_EXPORTED int libusb_handle_events_locked(struct timeval *tv)
1470 struct timeval poll_timeout;
1472 r = get_next_timeout(tv, &poll_timeout);
1474 /* timeout already expired */
1475 return handle_timeouts();
1478 return handle_events(&poll_timeout);
1482 * Determine the next internal timeout that libusb needs to handle. You only
1483 * need to use this function if you are calling poll() or select() or similar
1484 * on libusb's file descriptors yourself - you do not need to use it if you
1485 * are calling libusb_handle_events() or a variant directly.
1487 * You should call this function in your main loop in order to determine how
1488 * long to wait for select() or poll() to return results. libusb needs to be
1489 * called into at this timeout, so you should use it as an upper bound on
1490 * your select() or poll() call.
1492 * When the timeout has expired, call into libusb_handle_events_timeout()
1493 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
1495 * This function may return 1 (success) and an all-zero timeval. If this is
1496 * the case, it indicates that libusb has a timeout that has already expired
1497 * so you should call libusb_handle_events_timeout() or similar immediately.
1498 * A return code of 0 indicates that there are no pending timeouts.
1500 * \param tv output location for a relative time against the current
1501 * clock in which libusb must be called into in order to process timeout events
1502 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
1503 * or LIBUSB_ERROR_OTHER on failure
1505 API_EXPORTED int libusb_get_next_timeout(struct timeval *tv)
1507 struct usbi_transfer *transfer;
1508 struct timespec cur_ts;
1509 struct timeval cur_tv;
1510 struct timeval *next_timeout;
1514 pthread_mutex_lock(&flying_transfers_lock);
1515 if (list_empty(&flying_transfers)) {
1516 pthread_mutex_unlock(&flying_transfers_lock);
1517 usbi_dbg("no URBs, no timeout!");
1521 /* find next transfer which hasn't already been processed as timed out */
1522 list_for_each_entry(transfer, &flying_transfers, list) {
1523 if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
1528 pthread_mutex_unlock(&flying_transfers_lock);
1531 usbi_dbg("all URBs have already been processed for timeouts");
1535 next_timeout = &transfer->timeout;
1537 /* no timeout for next transfer */
1538 if (!timerisset(next_timeout)) {
1539 usbi_dbg("no URBs with timeouts, no timeout!");
1543 r = clock_gettime(CLOCK_MONOTONIC, &cur_ts);
1545 usbi_err("failed to read monotonic clock, errno=%d", errno);
1546 return LIBUSB_ERROR_OTHER;
1548 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
1550 if (timercmp(&cur_tv, next_timeout, >=)) {
1551 usbi_dbg("first timeout already expired");
1554 timersub(next_timeout, &cur_tv, tv);
1555 usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
1562 * Register notification functions for file descriptor additions/removals.
1563 * These functions will be invoked for every new or removed file descriptor
1564 * that libusb uses as an event source.
1566 * To remove notifiers, pass NULL values for the function pointers.
1568 * \param added_cb pointer to function for addition notifications
1569 * \param removed_cb pointer to function for removal notifications
1571 API_EXPORTED void libusb_set_pollfd_notifiers(libusb_pollfd_added_cb added_cb,
1572 libusb_pollfd_removed_cb removed_cb)
1574 fd_added_cb = added_cb;
1575 fd_removed_cb = removed_cb;
1578 /* Add a file descriptor to the list of file descriptors to be monitored.
1579 * events should be specified as a bitmask of events passed to poll(), e.g.
1580 * POLLIN and/or POLLOUT. */
1581 int usbi_add_pollfd(int fd, short events)
1583 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
1585 return LIBUSB_ERROR_NO_MEM;
1587 usbi_dbg("add fd %d events %d", fd, events);
1588 ipollfd->pollfd.fd = fd;
1589 ipollfd->pollfd.events = events;
1590 pthread_mutex_lock(&pollfds_lock);
1591 list_add(&ipollfd->list, &pollfds);
1592 pthread_mutex_unlock(&pollfds_lock);
1595 fd_added_cb(fd, events);
1599 /* Remove a file descriptor from the list of file descriptors to be polled. */
1600 void usbi_remove_pollfd(int fd)
1602 struct usbi_pollfd *ipollfd;
1605 usbi_dbg("remove fd %d", fd);
1606 pthread_mutex_lock(&pollfds_lock);
1607 list_for_each_entry(ipollfd, &pollfds, list)
1608 if (ipollfd->pollfd.fd == fd) {
1614 usbi_dbg("couldn't find fd %d to remove", fd);
1615 pthread_mutex_unlock(&pollfds_lock);
1619 list_del(&ipollfd->list);
1620 pthread_mutex_unlock(&pollfds_lock);
1627 * Retrieve a list of file descriptors that should be polled by your main loop
1628 * as libusb event sources.
1630 * The returned list is NULL-terminated and should be freed with free() when
1631 * done. The actual list contents must not be touched.
1633 * \returns a NULL-terminated list of libusb_pollfd structures, or NULL on
1636 API_EXPORTED const struct libusb_pollfd **libusb_get_pollfds(void)
1638 struct libusb_pollfd **ret = NULL;
1639 struct usbi_pollfd *ipollfd;
1643 pthread_mutex_lock(&pollfds_lock);
1644 list_for_each_entry(ipollfd, &pollfds, list)
1647 ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
1651 list_for_each_entry(ipollfd, &pollfds, list)
1652 ret[i++] = (struct libusb_pollfd *) ipollfd;
1656 pthread_mutex_unlock(&pollfds_lock);
1657 return (const struct libusb_pollfd **) ret;
1660 /* Backends call this from handle_events to report disconnection of a device.
1661 * The transfers get cancelled appropriately.
1663 void usbi_handle_disconnect(struct libusb_device_handle *handle)
1665 struct usbi_transfer *cur;
1666 struct usbi_transfer *to_cancel;
1668 usbi_dbg("device %d.%d",
1669 handle->dev->bus_number, handle->dev->device_address);
1671 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
1674 * this is a bit tricky because:
1675 * 1. we can't do transfer completion while holding flying_transfers_lock
1676 * 2. the transfers list can change underneath us - if we were to build a
1677 * list of transfers to complete (while holding look), the situation
1678 * might be different by the time we come to free them
1680 * so we resort to a loop-based approach as below
1681 * FIXME: is this still potentially racy?
1685 pthread_mutex_lock(&flying_transfers_lock);
1687 list_for_each_entry(cur, &flying_transfers, list)
1688 if (__USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
1692 pthread_mutex_unlock(&flying_transfers_lock);
1697 usbi_backend->clear_transfer_priv(to_cancel);
1698 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);