Pause event handling while opening and closing devices

Ludovic Rousseau found that crashes often occur if you close a device
while another thread is doing event handling.

Fix this by adding an internal control pipe, which the close routines
use to interrupt the event handler and obtain the event handling lock,
ensuring that no other thread is handling events while the device is
closed. After the close completes, it signals all the event handlers
to start up again using the usual mechanism.

Also modified libusb_open() to do a similar thing, so that event
handlers are interrupted in order to realise that a new poll fd has
appeared.

1 files changed, 12 insertions, 2 deletions

diff --git a/libusb/libusbi.h b/libusb/libusbi.h
index 43dd109..b51ba0b 100644
--- a/libusb/libusbi.h
+++ b/libusb/libusbi.h
@@ -144,6 +144,10 @@ struct libusb_context {
 	int debug;
 	int debug_fixed;
 
+	/* internal control pipe, used for interrupting event handling when
+	 * something needs to modify poll fds. */
+	int ctrl_pipe[2];
+
 	struct list_head usb_devs;
 	pthread_mutex_t usb_devs_lock;
 
@@ -159,10 +163,15 @@ struct libusb_context {
 	struct list_head flying_transfers;
 	pthread_mutex_t flying_transfers_lock;
 
-	/* list of poll fd's */
+	/* list of poll fds */
 	struct list_head pollfds;
 	pthread_mutex_t pollfds_lock;
 
+	/* a counter that is set when we want to interrupt event handling, in order
+	 * to modify the poll fd set. and a lock to protect it. */
+	unsigned int pollfd_modify;
+	pthread_mutex_t pollfd_modify_lock;
+
 	/* user callbacks for pollfd changes */
 	libusb_pollfd_added_cb fd_added_cb;
 	libusb_pollfd_removed_cb fd_removed_cb;
@@ -255,7 +264,8 @@ struct usb_descriptor_header {
 
 /* shared data and functions */
 
-void usbi_io_init(struct libusb_context *ctx);
+int usbi_io_init(struct libusb_context *ctx);
+void usbi_io_exit(struct libusb_context *ctx);
 
 struct libusb_device *usbi_alloc_device(struct libusb_context *ctx,
 	unsigned long session_id);