Don't release the gil if nobody is waiting for it

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/AsyncHandler.java

@@ -348,6 +348,10 @@ private GilReleaseScheduler(PythonContext ctx) {
 
         @Override
         public void run() {
+            if (!ctx.gilHasQueuedThreads()) {
+                // Don't release the gil if nobody is waiting for it
+                return;
+            }
             Thread gilOwner = ctx.getGilOwner();
             if (gilOwner != null) {
                 synchronized (this) {

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/PythonContext.java

@@ -2242,6 +2242,13 @@ Thread getGilOwner() {
         return globalInterpreterLock.getOwner();
     }
 
+    /**
+     * Should not be used outside of {@link AsyncHandler}
+     */
+    boolean gilHasQueuedThreads() {
+        return globalInterpreterLock.hasQueuedThreads();
+    }
+
     /**
      * Should not be called directly.
      *