[api] Introduce MicrotasksScope::IsRunningMicrotasks

Returns true while V8 executes microtasks

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/1920813002

Cr-Commit-Position: refs/heads/master@{#35769}

include/v8.h

@@ -5140,6 +5140,11 @@ class V8_EXPORT MicrotasksScope {
    */
   static int GetCurrentDepth(Isolate* isolate);
 
+  /**
+   * Returns true while microtasks are being executed.
+   */
+  static bool IsRunningMicrotasks(Isolate* isolate);
+
  private:
   internal::Isolate* const isolate_;
   bool run_;

src/api.cc

@@ -7913,6 +7913,10 @@ int MicrotasksScope::GetCurrentDepth(Isolate* v8Isolate) {
   return isolate->handle_scope_implementer()->GetMicrotasksScopeDepth();
 }
 
+bool MicrotasksScope::IsRunningMicrotasks(Isolate* v8Isolate) {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(v8Isolate);
+  return isolate->IsRunningMicrotasks();
+}
 
 String::Utf8Value::Utf8Value(v8::Local<v8::Value> obj)
     : str_(NULL), length_(0) {

src/isolate.cc

@@ -1858,6 +1858,7 @@ Isolate::Isolate(bool enable_serializer)
 #if TRACE_MAPS
       next_unique_sfi_id_(0),
 #endif
+      is_running_microtasks_(false),
       use_counter_callback_(NULL),
       basic_block_profiler_(NULL),
       cancelable_task_manager_(new CancelableTaskManager()),
@@ -2780,7 +2781,9 @@ void Isolate::RunMicrotasks() {
   // Increase call depth to prevent recursive callbacks.
   v8::Isolate::SuppressMicrotaskExecutionScope suppress(
       reinterpret_cast<v8::Isolate*>(this));
+  is_running_microtasks_ = true;
   RunMicrotasksInternal();
+  is_running_microtasks_ = false;
   FireMicrotasksCompletedCallback();
 }
 

src/isolate.h

@@ -1064,6 +1064,7 @@ class Isolate {
 
   void EnqueueMicrotask(Handle<Object> microtask);
   void RunMicrotasks();
+  bool IsRunningMicrotasks() const { return is_running_microtasks_; }
 
   void SetUseCounterCallback(v8::Isolate::UseCounterCallback callback);
   void CountUsage(v8::Isolate::UseCounterFeature feature);
@@ -1343,6 +1344,7 @@ class Isolate {
 
   // List of callbacks after microtasks were run.
   List<MicrotasksCompletedCallback> microtasks_completed_callbacks_;
+  bool is_running_microtasks_;
 
   v8::Isolate::UseCounterCallback use_counter_callback_;
   BasicBlockProfiler* basic_block_profiler_;

test/cctest/test-api.cc

@@ -20885,6 +20885,7 @@ TEST(CallCompletedCallbackTwoExceptions) {
 
 
 static void MicrotaskOne(const v8::FunctionCallbackInfo<Value>& info) {
+  CHECK(v8::MicrotasksScope::IsRunningMicrotasks(info.GetIsolate()));
   v8::HandleScope scope(info.GetIsolate());
   v8::MicrotasksScope microtasks(info.GetIsolate(),
                                  v8::MicrotasksScope::kDoNotRunMicrotasks);
@@ -20893,6 +20894,7 @@ static void MicrotaskOne(const v8::FunctionCallbackInfo<Value>& info) {
 
 
 static void MicrotaskTwo(const v8::FunctionCallbackInfo<Value>& info) {
+  CHECK(v8::MicrotasksScope::IsRunningMicrotasks(info.GetIsolate()));
   v8::HandleScope scope(info.GetIsolate());
   v8::MicrotasksScope microtasks(info.GetIsolate(),
                                  v8::MicrotasksScope::kDoNotRunMicrotasks);
@@ -20911,6 +20913,7 @@ static void MicrotaskThree(void* data) {
 TEST(EnqueueMicrotask) {
   LocalContext env;
   v8::HandleScope scope(env->GetIsolate());
+  CHECK(!v8::MicrotasksScope::IsRunningMicrotasks(env->GetIsolate()));
   CompileRun(
       "var ext1Calls = 0;"
       "var ext2Calls = 0;");