Allow microtasks to throw exceptions and handle them gracefully

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "ast.h"
 #include "bootstrapper.h"
@@ skipping 792 matching lines @@
   return heap()->exception();
 }
 
 
 Object* Isolate::TerminateExecution() {
   DoThrow(heap_.termination_exception(), NULL);
   return heap()->exception();
 }
 
 
+bool Isolate::IsExecutionTerminating() {
+  if (!IsInitialized()) return false;
+  if (has_scheduled_exception()) {
+    return scheduled_exception() == heap()->termination_exception();
+  }
+  return false;
+}
+
+
 void Isolate::CancelTerminateExecution() {
   if (try_catch_handler()) {
     try_catch_handler()->has_terminated_ = false;
   }
   if (has_pending_exception() &&
       pending_exception() == heap_.termination_exception()) {
     thread_local_top()->external_caught_exception_ = false;
     clear_pending_exception();
   }
   if (has_scheduled_exception() &&
@@ skipping 1451 matching lines @@
     HandleScope scope(this);
     int num_tasks = pending_microtask_count();
     Handle<FixedArray> queue(heap()->microtask_queue(), this);
     ASSERT(num_tasks <= queue->length());
     set_pending_microtask_count(0);
     heap()->set_microtask_queue(heap()->empty_fixed_array());
 
     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();
+      MaybeHandle<Object> result = Execution::Call(
+          this, microtask, factory()->undefined_value(), 0, NULL);
+      if (result.is_null()) {
+        // Microtasks should not throw unless the embedder has asked us to
+        // TerminateExecution.
+        ASSERT(IsExecutionTerminating());
+        handle_scope_implementer()->DecrementCallDepth();

[jochen (gone - plz use gerrit), 2014/05/22 07:45:38]

why not just break?

[adamk, 2014/05/22 08:02:16]

We're inside a while and a for loop. I would have added a goto but I didn't see
any others in v8...

+        return;
+      }
     }
   }
 
   handle_scope_implementer()->DecrementCallDepth();
 }
 
 
 } }  // namespace v8::internal