Reland 21529 - "Add a flag to d8 to invoke weak callbacks"

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 73bde94aad291cfbe6f20786073841c93d388071..f7d63ce1cd18c7eae9311fb50def7516232a80f2 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1211,9 +1211,16 @@ void SourceGroup::ExecuteInThread() {
         V8::ContextDisposedNotification();
         V8::IdleNotification(kLongIdlePauseInMs);
       }
+      if (Shell::options.invoke_weak_callbacks) {
+        // By sending a low memory notifications, we will try hard to collect
+        // all garbage and will therefore also invoke all weak callbacks of
+        // actually unreachable persistent handles.
+        V8::LowMemoryNotification();
+      }
     }
     done_semaphore_.Signal();
   } while (!Shell::options.last_run);
+
   isolate->Dispose();
 }
 
@@ -1274,6 +1281,11 @@ bool Shell::SetOptions(int argc, char* argv[]) {
     } else if (strcmp(argv[i], "--send-idle-notification") == 0) {
       options.send_idle_notification = true;
       argv[i] = NULL;
+    } else if (strcmp(argv[i], "--invoke-weak-callbacks") == 0) {
+      options.invoke_weak_callbacks = true;
+      // TODO(jochen) See issue 3351
+      options.send_idle_notification = true;
+      argv[i] = NULL;
     } else if (strcmp(argv[i], "-f") == 0) {
       // Ignore any -f flags for compatibility with other stand-alone
       // JavaScript engines.
@@ -1367,6 +1379,12 @@ int Shell::RunMain(Isolate* isolate, int argc, char* argv[]) {
     V8::ContextDisposedNotification();
     V8::IdleNotification(kLongIdlePauseInMs);
   }
+  if (options.invoke_weak_callbacks) {
+    // By sending a low memory notifications, we will try hard to collect all
+    // garbage and will therefore also invoke all weak callbacks of actually
+    // unreachable persistent handles.
+    V8::LowMemoryNotification();
+  }
 
 #ifndef V8_SHARED
   for (int i = 1; i < options.num_isolates; ++i) {