libusb: fix race condition on device close (#189)

Read callback may fire itself on its own even after its been
requested to stop and exactly before the calling code
waits for its completion in indefinite loop.

Explicitly preventing re-fireing the submission loop,
fixes the issue.

Fixes: #142.

Signed-off-by: Ihor Dutchak <ihor.youw@gmail.com>

libusb/hid.c

@@ -168,7 +168,7 @@ struct hid_device_ {
 	pthread_cond_t condition;
 	pthread_barrier_t barrier; /* Ensures correct startup sequence */
 	int shutdown_thread;
-	int cancelled;
+	int transfer_loop_finished;
 	struct libusb_transfer *transfer;
 
 	/* List of received input reports. */
@@ -787,13 +787,9 @@ static void read_callback(struct libusb_transfer *transfer)
 	}
 	else if (transfer->status == LIBUSB_TRANSFER_CANCELLED) {
 		dev->shutdown_thread = 1;
-		dev->cancelled = 1;
-		return;
 	}
 	else if (transfer->status == LIBUSB_TRANSFER_NO_DEVICE) {
 		dev->shutdown_thread = 1;
-		dev->cancelled = 1;
-		return;
 	}
 	else if (transfer->status == LIBUSB_TRANSFER_TIMED_OUT) {
 		//LOG("Timeout (normal)\n");
@@ -802,12 +798,17 @@ static void read_callback(struct libusb_transfer *transfer)
 		LOG("Unknown transfer code: %d\n", transfer->status);
 	}
 
+	if (dev->shutdown_thread) {
+		dev->transfer_loop_finished = 1;
+		return;
+	}
+
 	/* Re-submit the transfer object. */
 	res = libusb_submit_transfer(transfer);
 	if (res != 0) {
 		LOG("Unable to submit URB. libusb error code: %d\n", res);
 		dev->shutdown_thread = 1;
-		dev->cancelled = 1;
+		dev->transfer_loop_finished = 1;
 	}
 }
 
@@ -850,6 +851,7 @@ static void *read_thread(void *param)
 			    res != LIBUSB_ERROR_TIMEOUT &&
 			    res != LIBUSB_ERROR_OVERFLOW &&
 			    res != LIBUSB_ERROR_INTERRUPTED) {
+				dev->shutdown_thread = 1;
 				break;
 			}
 		}
@@ -859,8 +861,8 @@ static void *read_thread(void *param)
 	   if no transfers are pending, but that's OK. */
 	libusb_cancel_transfer(dev->transfer);
 
-	while (!dev->cancelled)
-		libusb_handle_events_completed(usb_context, &dev->cancelled);
+	while (!dev->transfer_loop_finished)
+		libusb_handle_events_completed(usb_context, &dev->transfer_loop_finished);
 
 	/* Now that the read thread is stopping, Wake any threads which are
 	   waiting on data (in hid_read_timeout()). Do this under a mutex to