io.c

linux 下的libusb 1.0.0版本

	r = ctx->pollfd_modify;
	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
	if (r) {
		usbi_dbg("someone else is modifying poll fds");
		return 1;
	}

	r = pthread_mutex_trylock(&ctx->events_lock);
	if (r)
		return 1;

	ctx->event_handler_active = 1;	
	return 0;
}

/** \ingroup poll
 * Acquire the event handling lock, blocking until successful acquisition if
 * it is contended. This lock is used to ensure that only one thread is
 * monitoring libusb event sources at any one time.
 *
 * You only need to use this lock if you are developing an application
 * which calls poll() or select() on libusb's file descriptors directly.
 * If you stick to libusb's event handling loop functions (e.g.
 * libusb_handle_events()) then you do not need to be concerned with this
 * locking.
 *
 * While holding this lock, you are trusted to actually be handling events.
 * If you are no longer handling events, you must call libusb_unlock_events()
 * as soon as possible.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \see \ref mtasync
 */
API_EXPORTED void libusb_lock_events(libusb_context *ctx)
{
	USBI_GET_CONTEXT(ctx);
	pthread_mutex_lock(&ctx->events_lock);
	ctx->event_handler_active = 1;
}

/** \ingroup poll
 * Release the lock previously acquired with libusb_try_lock_events() or
 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
 * on libusb_wait_for_event().
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \see \ref mtasync
 */
API_EXPORTED void libusb_unlock_events(libusb_context *ctx)
{
	USBI_GET_CONTEXT(ctx);
	ctx->event_handler_active = 0;
	pthread_mutex_unlock(&ctx->events_lock);

	/* FIXME: perhaps we should be a bit more efficient by not broadcasting
	 * the availability of the events lock when we are modifying pollfds
	 * (check ctx->pollfd_modify)? */
	pthread_mutex_lock(&ctx->event_waiters_lock);
	pthread_cond_broadcast(&ctx->event_waiters_cond);
	pthread_mutex_unlock(&ctx->event_waiters_lock);
}

/** \ingroup poll
 * Determine if it is still OK for this thread to be doing event handling.
 *
 * Sometimes, libusb needs to temporarily pause all event handlers, and this
 * is the function you should use before polling file descriptors to see if
 * this is the case.
 *
 * If this function instructs your thread to give up the events lock, you
 * should just continue the usual logic that is documented in \ref mtasync.
 * On the next iteration, your thread will fail to obtain the events lock,
 * and will hence become an event waiter.
 *
 * This function should be called while the events lock is held: you don't
 * need to worry about the results of this function if your thread is not
 * the current event handler.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \returns 1 if event handling can start or continue
 * \returns 0 if this thread must give up the events lock
 * \see \ref fullstory "Multi-threaded I/O: the full story"
 */
API_EXPORTED int libusb_event_handling_ok(libusb_context *ctx)
{
	int r;
	USBI_GET_CONTEXT(ctx);

	/* is someone else waiting to modify poll fds? if so, don't let this thread
	 * continue event handling */
	pthread_mutex_lock(&ctx->pollfd_modify_lock);
	r = ctx->pollfd_modify;
	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
	if (r) {
		usbi_dbg("someone else is modifying poll fds");
		return 0;
	}

	return 1;
}


/** \ingroup poll
 * Determine if an active thread is handling events (i.e. if anyone is holding
 * the event handling lock).
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \returns 1 if a thread is handling events
 * \returns 0 if there are no threads currently handling events
 * \see \ref mtasync
 */
API_EXPORTED int libusb_event_handler_active(libusb_context *ctx)
{
	int r;
	USBI_GET_CONTEXT(ctx);

	/* is someone else waiting to modify poll fds? if so, don't let this thread
	 * start event handling -- indicate that event handling is happening */
	pthread_mutex_lock(&ctx->pollfd_modify_lock);
	r = ctx->pollfd_modify;
	pthread_mutex_unlock(&ctx->pollfd_modify_lock);
	if (r) {
		usbi_dbg("someone else is modifying poll fds");
		return 1;
	}

	return ctx->event_handler_active;
}

/** \ingroup poll
 * Acquire the event waiters lock. This lock is designed to be obtained under
 * the situation where you want to be aware when events are completed, but
 * some other thread is event handling so calling libusb_handle_events() is not
 * allowed.
 *
 * You then obtain this lock, re-check that another thread is still handling
 * events, then call libusb_wait_for_event().
 *
 * You only need to use this lock if you are developing an application
 * which calls poll() or select() on libusb's file descriptors directly,
 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
 * If you stick to libusb's event handling loop functions (e.g.
 * libusb_handle_events()) then you do not need to be concerned with this
 * locking.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \see \ref mtasync
 */
API_EXPORTED void libusb_lock_event_waiters(libusb_context *ctx)
{
	USBI_GET_CONTEXT(ctx);
	pthread_mutex_lock(&ctx->event_waiters_lock);
}

/** \ingroup poll
 * Release the event waiters lock.
 * \param ctx the context to operate on, or NULL for the default context
 * \see \ref mtasync
 */
API_EXPORTED void libusb_unlock_event_waiters(libusb_context *ctx)
{
	USBI_GET_CONTEXT(ctx);
	pthread_mutex_unlock(&ctx->event_waiters_lock);
}

/** \ingroup poll
 * Wait for another thread to signal completion of an event. Must be called
 * with the event waiters lock held, see libusb_lock_event_waiters().
 *
 * This function will block until any of the following conditions are met:
 * -# The timeout expires
 * -# A transfer completes
 * -# A thread releases the event handling lock through libusb_unlock_events()
 *
 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
 * the callback for the transfer has completed. Condition 3 is important
 * because it means that the thread that was previously handling events is no
 * longer doing so, so if any events are to complete, another thread needs to
 * step up and start event handling.
 *
 * This function releases the event waiters lock before putting your thread
 * to sleep, and reacquires the lock as it is being woken up.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \param tv maximum timeout for this blocking function. A NULL value
 * indicates unlimited timeout.
 * \returns 0 after a transfer completes or another thread stops event handling
 * \returns 1 if the timeout expired
 * \see \ref mtasync
 */
API_EXPORTED int libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
{
	struct timespec timeout;
	int r;

	USBI_GET_CONTEXT(ctx);
	if (tv == NULL) {
		pthread_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
		return 0;
	}

	r = clock_gettime(CLOCK_REALTIME, &timeout);
	if (r < 0) {
		usbi_err(ctx, "failed to read realtime clock, error %d", errno);
		return LIBUSB_ERROR_OTHER;
	}

	timeout.tv_sec += tv->tv_sec;
	timeout.tv_nsec += tv->tv_usec * 1000;
	if (timeout.tv_nsec > 1000000000) {
		timeout.tv_nsec -= 1000000000;
		timeout.tv_sec++;
	}

	r = pthread_cond_timedwait(&ctx->event_waiters_cond,
		&ctx->event_waiters_lock, &timeout);
	return (r == ETIMEDOUT);
}

static void handle_timeout(struct usbi_transfer *itransfer)
{
	struct libusb_transfer *transfer =
		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
	int r;

	itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
	r = libusb_cancel_transfer(transfer);
	if (r < 0)
		usbi_warn(TRANSFER_CTX(transfer),
			"async cancel failed %d errno=%d", r, errno);
}

static int handle_timeouts(struct libusb_context *ctx)
{
	struct timespec systime_ts;
	struct timeval systime;
	struct usbi_transfer *transfer;
	int r = 0;

	USBI_GET_CONTEXT(ctx);
	pthread_mutex_lock(&ctx->flying_transfers_lock);
	if (list_empty(&ctx->flying_transfers))
		goto out;

	/* get current time */
	r = clock_gettime(CLOCK_MONOTONIC, &systime_ts);
	if (r < 0)
		goto out;

	TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);

	/* iterate through flying transfers list, finding all transfers that
	 * have expired timeouts */
	list_for_each_entry(transfer, &ctx->flying_transfers, list) {
		struct timeval *cur_tv = &transfer->timeout;

		/* if we've reached transfers of infinite timeout, we're all done */
		if (!timerisset(cur_tv))
			goto out;

		/* ignore timeouts we've already handled */
		if (transfer->flags & USBI_TRANSFER_TIMED_OUT)
			continue;

		/* if transfer has non-expired timeout, nothing more to do */
		if ((cur_tv->tv_sec > systime.tv_sec) ||
				(cur_tv->tv_sec == systime.tv_sec &&
					cur_tv->tv_usec > systime.tv_usec))
			goto out;
	
		/* otherwise, we've got an expired timeout to handle */
		handle_timeout(transfer);
	}

out:
	pthread_mutex_unlock(&ctx->flying_transfers_lock);
	return r;
}

/* do the actual event handling. assumes that no other thread is concurrently
 * doing the same thing. */
static int handle_events(struct libusb_context *ctx, struct timeval *tv)
{
	int r;
	struct usbi_pollfd *ipollfd;
	nfds_t nfds = 0;
	struct pollfd *fds;
	int i = -1;
	int timeout_ms;

	pthread_mutex_lock(&ctx->pollfds_lock);
	list_for_each_entry(ipollfd, &ctx->pollfds, list)
		nfds++;

	/* TODO: malloc when number of fd's changes, not on every poll */
	fds = malloc(sizeof(*fds) * nfds);
	if (!fds)
		return LIBUSB_ERROR_NO_MEM;

	list_for_each_entry(ipollfd, &ctx->pollfds, list) {
		struct libusb_pollfd *pollfd = &ipollfd->pollfd;
		int fd = pollfd->fd;
		i++;
		fds[i].fd = fd;
		fds[i].events = pollfd->events;
		fds[i].revents = 0;
	}
	pthread_mutex_unlock(&c