From: Martin Ling <redacted>
Date: Tue, 24 Mar 2015 19:06:17 +0000 (+0100)
Subject: Initial fix attempt for a thread-related issue on Windows.
X-Git-Tag: libsigrok-0.4.0~561
X-Git-Url: https://sigrok.org/gitweb/?p=libsigrok.git;a=commitdiff_plain;h=f6c30de4b031ab9a8d838c1ad6ff4118b03c0dc4

Initial fix attempt for a thread-related issue on Windows.

This is a partial fix for bug #343, which lead to a large amount of
handles being created, and eventually to a frontend "hang".

It's not yet a "full" fix as some issues are still observable,
but it successfully improves the situation on Windows to the extent
that frontend hangs due to large amounts of handles no longer seem
to happen.

Thanks to Boris Gjenero <redacted> for the debugging
efforts, testing, and updating of this patch!

Additionally, this seems to also fix a "SysClk LWLA hanging" bug
and apparently not receiving any samples during an acquisition
(tested on an LWLA1034).

This closes bug #328.
---

diff --git a/src/libsigrok-internal.h b/src/libsigrok-internal.h
index f3f6a026..a12b8d53 100644
--- a/src/libsigrok-internal.h
+++ b/src/libsigrok-internal.h
@@ -180,8 +180,8 @@ struct sr_context {
 #ifdef _WIN32
 	GThread *usb_thread;
 	gboolean usb_thread_running;
-	GMutex usb_mutex;
-	HANDLE usb_event;
+	HANDLE usb_wait_request_event;
+	HANDLE usb_wait_complete_event;
 	GPollFD usb_pollfd;
 	sr_receive_data_callback usb_cb;
 	void *usb_cb_data;
diff --git a/src/usb.c b/src/usb.c
index 9c34b38a..b0ea618c 100644
--- a/src/usb.c
+++ b/src/usb.c
@@ -178,32 +178,48 @@ SR_PRIV int sr_usb_open(libusb_context *usb_ctx, struct sr_usb_dev_inst *usb)
 }
 
 #ifdef _WIN32
+/* Thread used to run libusb_wait_for_event() and set a pollable event. */
 static gpointer usb_thread(gpointer data)
 {
 	struct sr_context *ctx = data;
 
 	while (ctx->usb_thread_running) {
-		g_mutex_lock(&ctx->usb_mutex);
+		/* Acquire event waiters lock, needed for libusb_wait_for_event(). */
+		libusb_lock_event_waiters(ctx->libusb_ctx);
+		/* Wait for any libusb event. The main thread can interrupt this wait
+		 * by calling libusb_unlock_events(). */
 		libusb_wait_for_event(ctx->libusb_ctx, NULL);
-		SetEvent(ctx->usb_event);
-		g_mutex_unlock(&ctx->usb_mutex);
-		g_thread_yield();
+		/* Release event waiters lock. */
+		libusb_unlock_event_waiters(ctx->libusb_ctx);
+		/* Set event that the main loop will be polling on. */
+		SetEvent(ctx->usb_wait_complete_event);
+		/* Wait for the main thread to signal us to run again. */
+		WaitForSingleObject(ctx->usb_wait_request_event, INFINITE);
+		ResetEvent(ctx->usb_wait_request_event);
 	}
 
 	return NULL;
 }
 
+/* Callback wrapper run when main g_poll() gets a USB event or timeout. */
 static int usb_callback(int fd, int revents, void *cb_data)
 {
 	struct sr_context *ctx = cb_data;
 	int ret;
 
-	g_mutex_lock(&ctx->usb_mutex);
+	/* Run registered callback to handle libusb events. */
 	ret = ctx->usb_cb(fd, revents, ctx->usb_cb_data);
 
-	if (ctx->usb_thread_running) {
-		ResetEvent(ctx->usb_event);
-		g_mutex_unlock(&ctx->usb_mutex);
+	/* Were we triggered by an event from the wait thread, rather than by a
+	 * timeout? */
+	int triggered_by_event = (revents & G_IO_IN);
+
+	/* If so, and if the USB event source has not been removed from the
+	 * session, reset the event that woke us and tell the wait thread to start
+	 * waiting for events again. */
+	if (triggered_by_event && ctx->usb_thread_running) {
+		ResetEvent(ctx->usb_wait_complete_event);
+		SetEvent(ctx->usb_wait_request_event);
 	}
 
 	return ret;
@@ -219,11 +235,14 @@ SR_PRIV int usb_source_add(struct sr_session *session, struct sr_context *ctx,
 	}
 
 #ifdef _WIN32
-	ctx->usb_event = CreateEvent(NULL, TRUE, FALSE, NULL);
-	g_mutex_init(&ctx->usb_mutex);
+	/* Create events used to signal between main and USB wait threads. */
+	ctx->usb_wait_request_event = CreateEvent(NULL, TRUE, FALSE, NULL);
+	ctx->usb_wait_complete_event = CreateEvent(NULL, TRUE, FALSE, NULL);
+	/* Start USB wait thread. */
 	ctx->usb_thread_running = TRUE;
 	ctx->usb_thread = g_thread_new("usb", usb_thread, ctx);
-	ctx->usb_pollfd.fd = ctx->usb_event;
+	/* Add event, set by USB wait thread, to session poll set. */
+	ctx->usb_pollfd.fd = ctx->usb_wait_complete_event;
 	ctx->usb_pollfd.events = G_IO_IN;
 	ctx->usb_cb = cb;
 	ctx->usb_cb_data = cb_data;
@@ -250,13 +269,17 @@ SR_PRIV int usb_source_remove(struct sr_session *session, struct sr_context *ctx
 		return SR_OK;
 
 #ifdef _WIN32
+	/* Signal the USB wait thread to stop, then unblock it so it does. */
 	ctx->usb_thread_running = FALSE;
-	g_mutex_unlock(&ctx->usb_mutex);
+	SetEvent(ctx->usb_wait_request_event);
 	libusb_unlock_events(ctx->libusb_ctx);
+	/* Wait for USB wait thread to terminate. */
 	g_thread_join(ctx->usb_thread);
-	g_mutex_clear(&ctx->usb_mutex);
+	/* Remove USB event from session poll set. */
 	sr_session_source_remove_pollfd(session, &ctx->usb_pollfd);
-	CloseHandle(ctx->usb_event);
+	/* Close event handles that were used between threads. */
+	CloseHandle(ctx->usb_wait_request_event);
+	CloseHandle(ctx->usb_wait_complete_event);
 #else
 	const struct libusb_pollfd **lupfd;
 	unsigned int i;