Fix a race condition

See http://sourceforge.net/mailarchive/message.php?msg_name=4BD920C5.3090909%40argyllcms.com

3 files changed, 42 insertions, 18 deletions

diff --git a/libusb/io.c b/libusb/io.c
index ab37e8d..7ab811e 100644
--- a/libusb/io.c
+++ b/libusb/io.c
@@ -1948,8 +1948,8 @@ static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
  * non-blocking mode
  * \returns 0 on success, or a LIBUSB_ERROR code on failure
  */
-int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
-	struct timeval *tv)
+int API_EXPORTED libusb_handle_events_timeout_check(libusb_context *ctx,
+	struct timeval *tv, int *completed)
 {
 	int r;
 	struct timeval poll_timeout;
@@ -1963,8 +1963,12 @@ int API_EXPORTED libusb_handle_events_timeout(libusb_context *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);
+		r = 0;
+		if (completed == NULL || !*completed) {
+			/* we obtained the event lock: do our own event handling */
+			usbi_dbg("doing our own event handling");
+			r = handle_events(ctx, &poll_timeout);
+		}
 		libusb_unlock_events(ctx);
 		return r;
 	}
@@ -1973,16 +1977,18 @@ retry:
 	 * 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;
+	if (completed == NULL || !*completed) {
+		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, wait for notification");
+		r = libusb_wait_for_event(ctx, &poll_timeout);
 	}
-
-	usbi_dbg("another thread is doing event handling");
-	r = libusb_wait_for_event(ctx, &poll_timeout);
 	libusb_unlock_event_waiters(ctx);
 
 	if (r < 0)
@@ -1993,6 +1999,21 @@ retry:
 		return 0;
 }
 
+API_EXPORTED int libusb_handle_events_timeout(libusb_context *ctx,
+	struct timeval *tv)
+{
+	return libusb_handle_events_timeout_check(ctx, tv, NULL); 
+}
+
+API_EXPORTED int libusb_handle_events_check(libusb_context *ctx,
+	int *completed)
+{
+	struct timeval tv;
+	tv.tv_sec = 60;
+	tv.tv_usec = 0;
+	return libusb_handle_events_timeout_check(ctx, &tv, completed);
+}
+
 /** \ingroup poll
  * Handle any pending events in blocking mode. There is currently a timeout
  * hardcoded at 60 seconds but we plan to make it unlimited in future. For
@@ -2007,7 +2028,7 @@ int API_EXPORTED libusb_handle_events(libusb_context *ctx)
 	struct timeval tv;
 	tv.tv_sec = 60;
 	tv.tv_usec = 0;
-	return libusb_handle_events_timeout(ctx, &tv);
+	return libusb_handle_events_timeout_check(ctx, &tv, NULL);
 }
 
 /** \ingroup poll
diff --git a/libusb/libusb.h b/libusb/libusb.h
index e2cc606..d46c68b 100644
--- a/libusb/libusb.h
+++ b/libusb/libusb.h
@@ -1275,7 +1275,10 @@ int LIBUSB_CALL libusb_wait_for_event(libusb_context *ctx, struct timeval *tv);
 
 int LIBUSB_CALL libusb_handle_events_timeout(libusb_context *ctx,
 	struct timeval *tv);
+int LIBUSB_CALL libusb_handle_events_timeout_check(libusb_context *ctx,
+	struct timeval *tv, int *completed);
 int LIBUSB_CALL libusb_handle_events(libusb_context *ctx);
+int LIBUSB_CALL libusb_handle_events_check(libusb_context *ctx, int *completed);
 int LIBUSB_CALL libusb_handle_events_locked(libusb_context *ctx,
 	struct timeval *tv);
 int LIBUSB_CALL libusb_pollfds_handle_timeouts(libusb_context *ctx);
diff --git a/libusb/sync.c b/libusb/sync.c
index f6dc2a7..d040d98 100644
--- a/libusb/sync.c
+++ b/libusb/sync.c
@@ -102,13 +102,13 @@ int API_EXPORTED libusb_control_transfer(libusb_device_handle *dev_handle,
 	}
 
 	while (!completed) {
-		r = libusb_handle_events(HANDLE_CTX(dev_handle));
+		r = libusb_handle_events_check(HANDLE_CTX(dev_handle), &completed);
 		if (r < 0) {
 			if (r == LIBUSB_ERROR_INTERRUPTED)
 				continue;
 			libusb_cancel_transfer(transfer);
 			while (!completed)
-				if (libusb_handle_events(HANDLE_CTX(dev_handle)) < 0)
+				if (libusb_handle_events_check(HANDLE_CTX(dev_handle), &completed) < 0)
 					break;
 			libusb_free_transfer(transfer);
 			return r;
@@ -172,13 +172,13 @@ static int do_sync_bulk_transfer(struct libusb_device_handle *dev_handle,
 	}
 
 	while (!completed) {
-		r = libusb_handle_events(HANDLE_CTX(dev_handle));
+		r = libusb_handle_events_check(HANDLE_CTX(dev_handle), &completed);
 		if (r < 0) {
 			if (r == LIBUSB_ERROR_INTERRUPTED)
 				continue;
 			libusb_cancel_transfer(transfer);
 			while (!completed)
-				if (libusb_handle_events(HANDLE_CTX(dev_handle)) < 0)
+				if (libusb_handle_events_check(HANDLE_CTX(dev_handle), &completed) < 0)
 					break;
 			libusb_free_transfer(transfer);
 			return r;