gl: Fix a fence deadlock in fence::wait_for_signal

gl: Fix potential race condition when executing local work queue

rpcs3/Emu/RSX/GL/GLGSRender.cpp

@@ -942,6 +942,8 @@ void GLGSRender::do_local_task()
 {
 	std::lock_guard<std::mutex> lock(queue_guard);
 
+	work_queue.remove_if([](work_item &q) { return q.received; });
+
 	for (work_item& q: work_queue)
 	{
 		std::unique_lock<std::mutex> lock(q.guard_mutex);
@@ -954,8 +956,6 @@ void GLGSRender::do_local_task()
 		lock.unlock();
 		q.cv.notify_one();
 	}
-
-	work_queue.clear();
 }
 
 work_item& GLGSRender::post_flush_request(u32 address)

rpcs3/Emu/RSX/GL/GLGSRender.h

@@ -17,9 +17,10 @@ struct work_item
 	std::condition_variable cv;
 	std::mutex guard_mutex;
 	
-	u32  address_to_flush;
+	u32  address_to_flush = 0;
-	bool processed;
+	bool processed = false;
-	bool result;
+	bool result = false;
+	bool received = false;
 };
 
 struct gcm_buffer_info

rpcs3/Emu/RSX/GL/GLHelpers.h

@@ -80,6 +80,7 @@ namespace gl
 		void create()
 		{
 			m_value = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
+			flags = GL_SYNC_FLUSH_COMMANDS_BIT;
 		}
 
 		void destroy()
@@ -132,7 +133,7 @@ namespace gl
 			{
 				if (flags)
 				{
-					err = glClientWaitSync(m_value, flags, 1000);
+					err = glClientWaitSync(m_value, flags, 0);
 					flags = 0;
 
 					switch (err)

rpcs3/Emu/RSX/GL/GLTextureCache.cpp

@@ -54,7 +54,7 @@ namespace gl
 				task.cv.wait(lock, [&task] { return task.processed; });
 			}
 
-			verify(HERE), task.result == true;
+			task.received = true;
 			return task.result;
 		}