io.c

最新的libusb库

	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(&ctx->pollfds_lock);

	timeout_ms = (tv->tv_sec * 1000) + (tv->tv_usec / 1000);

	/* round up to next millisecond */
	if (tv->tv_usec % 1000)
		timeout_ms++;

	usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
	r = poll(fds, nfds, timeout_ms);
	usbi_dbg("poll() returned %d", r);
	if (r == 0) {
		free(fds);
		return handle_timeouts(ctx);
	} else if (r == -1 && errno == EINTR) {
		free(fds);
		return LIBUSB_ERROR_INTERRUPTED;
	} else if (r < 0) {
		free(fds);
		usbi_err(ctx, "poll failed %d err=%d\n", r, errno);
		return LIBUSB_ERROR_IO;
	}

	r = usbi_backend->handle_events(ctx, fds, nfds, r);
	if (r)
		usbi_err(ctx, "backend handle_events failed with error %d", r);

	free(fds);
	return r;
}

/* returns the smallest of:
 *  1. timeout of next URB
 *  2. user-supplied timeout
 * returns 1 if there is an already-expired timeout, otherwise returns 0
 * and populates out
 */
static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
	struct timeval *out)
{
	struct timeval timeout;
	int r = libusb_get_next_timeout(ctx, &timeout);
	if (r) {
		/* timeout already expired? */
		if (!timerisset(&timeout))
			return 1;

		/* choose the smallest of next URB timeout or user specified timeout */
		if (timercmp(&timeout, tv, <))
			*out = timeout;
		else
			*out = *tv;
	} else {
		*out = *tv;
	}
	return 0;
}

/** \ingroup poll
 * Handle any pending events.
 *
 * libusb determines "pending events" by checking if any timeouts have expired
 * and by checking the set of file descriptors for activity.
 *
 * If a zero timeval is passed, this function will handle any already-pending
 * events and then immediately return in non-blocking style.
 *
 * If a non-zero timeval is passed and no events are currently pending, this
 * function will block waiting for events to handle up until the specified
 * timeout. If an event arrives or a signal is raised, this function will
 * return early.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \param tv the maximum time to block waiting for events, or zero for
 * non-blocking mode
 * \returns 0 on success, or a LIBUSB_ERROR code on failure
 */
API_EXPORTED int libusb_handle_events_timeout(libusb_context *ctx,
	struct timeval *tv)
{
	int r;
	struct timeval poll_timeout;

	USBI_GET_CONTEXT(ctx);
	r = get_next_timeout(ctx, tv, &poll_timeout);
	if (r) {
		/* timeout already expired */
		return handle_timeouts(ctx);
	}

retry:
	if (libusb_try_lock_events(ctx) == 0) {
		/* we obtained the event lock: do our own event handling */
		r = handle_events(ctx, &poll_timeout);
		libusb_unlock_events(ctx);
		return r;
	}

	/* another thread is doing event handling. wait for pthread events that
	 * notify event completion. */
	libusb_lock_event_waiters(ctx);

	if (!libusb_event_handler_active(ctx)) {
		/* we hit a race: whoever was event handling earlier finished in the
		 * time it took us to reach this point. try the cycle again. */
		libusb_unlock_event_waiters(ctx);
		usbi_dbg("event handler was active but went away, retrying");
		goto retry;
	}

	usbi_dbg("another thread is doing event handling");
	r = libusb_wait_for_event(ctx, &poll_timeout);
	libusb_unlock_event_waiters(ctx);

	if (r < 0)
		return r;
	else if (r == 1)
		return handle_timeouts(ctx);
	else
		return 0;
}

/** \ingroup poll
 * Handle any pending events in blocking mode with a sensible timeout. This
 * timeout is currently hardcoded at 2 seconds but we may change this if we
 * decide other values are more sensible. For finer control over whether this
 * function is blocking or non-blocking, or the maximum timeout, use
 * libusb_handle_events_timeout() instead.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \returns 0 on success, or a LIBUSB_ERROR code on failure
 */
API_EXPORTED int libusb_handle_events(libusb_context *ctx)
{
	struct timeval tv;
	tv.tv_sec = 2;
	tv.tv_usec = 0;
	return libusb_handle_events_timeout(ctx, &tv);
}

/** \ingroup poll
 * Handle any pending events by polling file descriptors, without checking if
 * any other threads are already doing so. Must be called with the event lock
 * held, see libusb_lock_events().
 *
 * This function is designed to be called under the situation where you have
 * taken the event lock and are calling poll()/select() directly on libusb's
 * file descriptors (as opposed to using libusb_handle_events() or similar).
 * You detect events on libusb's descriptors, so you then call this function
 * with a zero timeout value (while still holding the event lock).
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \param tv the maximum time to block waiting for events, or zero for
 * non-blocking mode
 * \returns 0 on success, or a LIBUSB_ERROR code on failure
 * \see \ref mtasync
 */
API_EXPORTED int libusb_handle_events_locked(libusb_context *ctx,
	struct timeval *tv)
{
	int r;
	struct timeval poll_timeout;

	USBI_GET_CONTEXT(ctx);
	r = get_next_timeout(ctx, tv, &poll_timeout);
	if (r) {
		/* timeout already expired */
		return handle_timeouts(ctx);
	}

	return handle_events(ctx, &poll_timeout);
}

/** \ingroup poll
 * Determine the next internal timeout that libusb needs to handle. You only
 * need to use this function if you are calling poll() or select() or similar
 * on libusb's file descriptors yourself - you do not need to use it if you
 * are calling libusb_handle_events() or a variant directly.
 * 
 * You should call this function in your main loop in order to determine how
 * long to wait for select() or poll() to return results. libusb needs to be
 * called into at this timeout, so you should use it as an upper bound on
 * your select() or poll() call.
 *
 * When the timeout has expired, call into libusb_handle_events_timeout()
 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
 *
 * This function may return 1 (success) and an all-zero timeval. If this is
 * the case, it indicates that libusb has a timeout that has already expired
 * so you should call libusb_handle_events_timeout() or similar immediately.
 * A return code of 0 indicates that there are no pending timeouts.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \param tv output location for a relative time against the current
 * clock in which libusb must be called into in order to process timeout events
 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
 * or LIBUSB_ERROR_OTHER on failure
 */
API_EXPORTED int libusb_get_next_timeout(libusb_context *ctx,
	struct timeval *tv)
{
	struct usbi_transfer *transfer;
	struct timespec cur_ts;
	struct timeval cur_tv;
	struct timeval *next_timeout;
	int r;
	int found = 0;

	USBI_GET_CONTEXT(ctx);
	pthread_mutex_lock(&ctx->flying_transfers_lock);
	if (list_empty(&ctx->flying_transfers)) {
		pthread_mutex_unlock(&ctx->flying_transfers_lock);
		usbi_dbg("no URBs, no timeout!");
		return 0;
	}

	/* find next transfer which hasn't already been processed as timed out */
	list_for_each_entry(transfer, &ctx->flying_transfers, list) {
		if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
			found = 1;
			break;
		}
	}
	pthread_mutex_unlock(&ctx->flying_transfers_lock);

	if (!found) {
		usbi_dbg("all URBs have already been processed for timeouts");
		return 0;
	}

	next_timeout = &transfer->timeout;

	/* no timeout for next transfer */
	if (!timerisset(next_timeout)) {
		usbi_dbg("no URBs with timeouts, no timeout!");
		return 0;
	}

	r = clock_gettime(CLOCK_MONOTONIC, &cur_ts);
	if (r < 0) {
		usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
		return LIBUSB_ERROR_OTHER;
	}
	TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);

	if (timercmp(&cur_tv, next_timeout, >=)) {
		usbi_dbg("first timeout already expired");
		timerclear(tv);
	} else {
		timersub(next_timeout, &cur_tv, tv);
		usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
	}

	return 1;
}

/** \ingroup poll
 * Register notification functions for file descriptor additions/removals.
 * These functions will be invoked for every new or removed file descriptor
 * that libusb uses as an event source.
 *
 * To remove notifiers, pass NULL values for the function pointers.
 *
 * \param ctx the context to operate on, or NULL for the default context
 * \param added_cb pointer to function for addition notifications
 * \param removed_cb pointer to function for removal notifications
 * \param user_data User data to be passed back to callbacks (useful for
 * passing context information)
 */
API_EXPORTED void libusb_set_pollfd_notifiers(libusb_context *ctx,
	libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
	void *user_data)
{
	USBI_GET_CONTEXT(ctx);
	ctx->fd_added_cb