[winpr,synch] Fix starvation in pollset_poll caused by emscripten_sleep

Recent changes in `pollset_poll` added yielding the process using
`emscripten_sleep` so event handlers can have time to process data and
set events.

However calling `emscripten_sleep` on every iteration when checking the
pollset caused process starvation which slowed down the whole session
massively.

This commit fixes this issue by checking for signaled events 10 times
before actually causing a yield. This avoids possible deadlocks while
not slowing down the whole session pipeline.

winpr/libwinpr/synch/pollset.c

@@ -148,9 +148,18 @@ int pollset_poll(WINPR_POLL_SET* set, DWORD dwMilliseconds)
 		if (ret >= 0)
 		{
 #if defined(__EMSCRIPTEN__)
-			/* Yield in emscripten so event handlers can be processed */
+			/* If we have tried 10 times unsuccessfully we will yield in emscripten so pending event
+			 * handlers might be run */
 			if (ret == 0)
-				emscripten_sleep(0);
+			{
+				if (++set->yieldCounter > 10)
+				{
+					emscripten_sleep(0);
+					set->yieldCounter = 0;
+				}
+			}
+			else
+				set->yieldCounter = 0;
 #endif
 			return ret;
 		}

winpr/libwinpr/synch/pollset.h

@@ -55,6 +55,9 @@ struct winpr_poll_set
 #endif
 	size_t fillIndex;
 	size_t size;
+#if defined(__EMSCRIPTEN__)
+	size_t yieldCounter;
+#endif
 };
 
 typedef struct winpr_poll_set WINPR_POLL_SET;