wait for GC to clean up weak refs

Author: qunaibit

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiContext.java

@@ -958,7 +958,7 @@ public void exitCApiContext() {
              * deallocating objects may run arbitrary guest code that can again call into the
              * interpreter.
              */
-            CApiTransitions.pollReferenceQueue();
+            CApiTransitions.exitPollCleanup();
             PythonThreadState threadState = getContext().getThreadState(getContext().getLanguage());
             Object nativeThreadState = PThreadState.getNativeThreadState(threadState);
             if (nativeThreadState != null) {

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/transitions/CApiTransitions.java

@@ -407,6 +407,21 @@ public static PyCapsuleReference registerPyCapsuleDestructor(PyCapsule capsule)
         return ref;
     }
 
+    @TruffleBoundary
+    public static void exitPollCleanup() {
+        PythonContext context = PythonContext.get(null);
+        HandleContext handleContext = context.nativeContext;
+        int len = handleContext.nativeStubLookup.length;
+        int idx = 0;
+        while (idx < len) {
+            if (handleContext.nativeStubLookup[idx] == null || handleContext.nativeStubLookup[idx].get() != null) {
+                idx++;
+            } else {
+                pollReferenceQueue();
+            }
+        }
+    }
+
     @TruffleBoundary
     @SuppressWarnings("try")
     public static void pollReferenceQueue() {