core: Only interrupt event handlers as necessary during libusb_open()

The current behavior of libusb_open() unconditionally interrupts
any event handlers via usbi_fd_notification(). However, not all
backends, namely Win/WinCE, make changes to the pollfd list during
a device open.

This change adds a new CAP for backends (HAS_POLLABLE_DEVICE_FD),
and libusb_open() will only call usbi_fd_notification() if the
backend declares this capability.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

1 files changed, 9 insertions, 7 deletions

diff --git a/libusb/core.c b/libusb/core.c
index f3d7ece..1b74493 100644
--- a/libusb/core.c
+++ b/libusb/core.c
@@ -1125,13 +1125,15 @@ int API_EXPORTED libusb_open(libusb_device *dev,
 	usbi_mutex_unlock(&ctx->open_devs_lock);
 	*handle = _handle;
 
-	/* At this point, we want to interrupt any existing event handlers so
-	 * that they realise the addition of the new device's poll fd. One
-	 * example when this is desirable is if the user is running a separate
-	 * dedicated libusb events handling thread, which is running with a long
-	 * or infinite timeout. We want to interrupt that iteration of the loop,
-	 * so that it picks up the new fd, and then continues. */
-	usbi_fd_notification(ctx);
+	if (usbi_backend->caps & USBI_CAP_HAS_POLLABLE_DEVICE_FD) {
+		/* At this point, we want to interrupt any existing event handlers so
+		 * that they realise the addition of the new device's poll fd. One
+		 * example when this is desirable is if the user is running a separate
+		 * dedicated libusb events handling thread, which is running with a long
+		 * or infinite timeout. We want to interrupt that iteration of the loop,
+		 * so that it picks up the new fd, and then continues. */
+		usbi_fd_notification(ctx);
+	}
 
 	return 0;
 }