Allow microtasks to throw exceptions and handle them gracefully

If the embedder calls V8::TerminateExecution while we're running microtasks, bail out
and clear any pending microtasks.

All other exceptions are simply swallowed. No current Blink or V8 microtasks throw, this
just ensures something sane happens if another embedder decides to pass a throwing
microtask (or if ours unexpectedly throw due to, e.g., stack exhaustion).

BUG=371566
LOG=Y
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/294943009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21574 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -4380,6 +4380,7 @@ class V8_EXPORT Isolate {
 
   /**
    * Experimental: Runs the Microtask Work Queue until empty
+   * Any exceptions thrown by microtask callbacks are swallowed.
    */
   void RunMicrotasks();
 

src/isolate.cc

@@ -2254,11 +2254,11 @@ void Isolate::FireCallCompletedCallback() {
   if (!handle_scope_implementer()->CallDepthIsZero()) return;
   if (run_microtasks) RunMicrotasks();
   // Fire callbacks.  Increase call depth to prevent recursive callbacks.
-  handle_scope_implementer()->IncrementCallDepth();
+  v8::Isolate::SuppressMicrotaskExecutionScope suppress(
+      reinterpret_cast<v8::Isolate*>(this));
   for (int i = 0; i < call_completed_callbacks_.length(); i++) {
     call_completed_callbacks_.at(i)();
   }
-  handle_scope_implementer()->DecrementCallDepth();
 }
 
 
@@ -2288,7 +2288,8 @@ void Isolate::RunMicrotasks() {
   // ASSERT(handle_scope_implementer()->CallDepthIsZero());
 
   // Increase call depth to prevent recursive callbacks.
-  handle_scope_implementer()->IncrementCallDepth();
+  v8::Isolate::SuppressMicrotaskExecutionScope suppress(
+      reinterpret_cast<v8::Isolate*>(this));
 
   while (pending_microtask_count() > 0) {
     HandleScope scope(this);
@@ -2301,13 +2302,20 @@ void Isolate::RunMicrotasks() {
     for (int i = 0; i < num_tasks; i++) {
       HandleScope scope(this);
       Handle<JSFunction> microtask(JSFunction::cast(queue->get(i)), this);
-      // TODO(adamk): This should ignore/clear exceptions instead of Checking.
-      Execution::Call(this, microtask, factory()->undefined_value(),
-                      0, NULL).Check();
+      Handle<Object> exception;
+      MaybeHandle<Object> result = Execution::TryCall(
+          microtask, factory()->undefined_value(), 0, NULL, &exception);
+      // If execution is terminating, just bail out.
+      if (result.is_null() &&
+          !exception.is_null() &&
+          *exception == heap()->termination_exception()) {
+        // Clear out any remaining callbacks in the queue.
+        heap()->set_microtask_queue(heap()->empty_fixed_array());
+        set_pending_microtask_count(0);
+        return;
+      }
     }
   }
-
-  handle_scope_implementer()->DecrementCallDepth();
 }
 
 

test/cctest/test-api.cc

@@ -20777,6 +20777,43 @@ TEST(EnqueueMicrotask) {
 }
 
 
+static void MicrotaskExceptionOne(
+    const v8::FunctionCallbackInfo<Value>& info) {
+  v8::HandleScope scope(info.GetIsolate());
+  CompileRun("exception1Calls++;");
+  info.GetIsolate()->ThrowException(
+      v8::Exception::Error(v8_str("first")));
+}
+
+
+static void MicrotaskExceptionTwo(
+    const v8::FunctionCallbackInfo<Value>& info) {
+  v8::HandleScope scope(info.GetIsolate());
+  CompileRun("exception2Calls++;");
+  info.GetIsolate()->ThrowException(
+      v8::Exception::Error(v8_str("second")));
+}
+
+
+TEST(RunMicrotasksIgnoresThrownExceptions) {
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope scope(isolate);
+  CompileRun(
+      "var exception1Calls = 0;"
+      "var exception2Calls = 0;");
+  isolate->EnqueueMicrotask(
+      Function::New(isolate, MicrotaskExceptionOne));
+  isolate->EnqueueMicrotask(
+      Function::New(isolate, MicrotaskExceptionTwo));
+  TryCatch try_catch;
+  CompileRun("1+1;");
+  CHECK(!try_catch.HasCaught());
+  CHECK_EQ(1, CompileRun("exception1Calls")->Int32Value());
+  CHECK_EQ(1, CompileRun("exception2Calls")->Int32Value());
+}
+
+
 TEST(SetAutorunMicrotasks) {
   LocalContext env;
   v8::HandleScope scope(env->GetIsolate());

test/cctest/test-thread-termination.cc

@@ -358,3 +358,47 @@ TEST(TerminateCancelTerminateFromThreadItself) {
   // Check that execution completed with correct return value.
   CHECK(v8::Script::Compile(source)->Run()->Equals(v8_str("completed")));
 }
+
+
+void MicrotaskShouldNotRun(const v8::FunctionCallbackInfo<v8::Value>& info) {
+  CHECK(false);
+}
+
+
+void MicrotaskLoopForever(const v8::FunctionCallbackInfo<v8::Value>& info) {
+  v8::Isolate* isolate = info.GetIsolate();
+  v8::HandleScope scope(isolate);
+  // Enqueue another should-not-run task to ensure we clean out the queue
+  // when we terminate.
+  isolate->EnqueueMicrotask(v8::Function::New(isolate, MicrotaskShouldNotRun));
+  CompileRun("terminate(); while (true) { }");
+  CHECK(v8::V8::IsExecutionTerminating());
+}
+
+
+TEST(TerminateFromOtherThreadWhileMicrotaskRunning) {
+  semaphore = new v8::internal::Semaphore(0);
+  TerminatorThread thread(CcTest::i_isolate());
+  thread.Start();
+
+  v8::Isolate* isolate = CcTest::isolate();
+  isolate->SetAutorunMicrotasks(false);
+  v8::HandleScope scope(isolate);
+  v8::Handle<v8::ObjectTemplate> global =
+      CreateGlobalTemplate(CcTest::isolate(), Signal, DoLoop);
+  v8::Handle<v8::Context> context =
+      v8::Context::New(CcTest::isolate(), NULL, global);
+  v8::Context::Scope context_scope(context);
+  isolate->EnqueueMicrotask(v8::Function::New(isolate, MicrotaskLoopForever));
+  // The second task should never be run because we bail out if we're
+  // terminating.
+  isolate->EnqueueMicrotask(v8::Function::New(isolate, MicrotaskShouldNotRun));
+  isolate->RunMicrotasks();
+
+  v8::V8::CancelTerminateExecution(isolate);
+  isolate->RunMicrotasks();  // should not run MicrotaskShouldNotRun
+
+  thread.Join();
+  delete semaphore;
+  semaphore = NULL;
+}