use v8 Microtask Queue

Source/core/dom/Microtask.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 15 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/dom/Microtask.h"
 
 #include "bindings/v8/V8PerIsolateData.h"
 #include "wtf/Vector.h"
+#include <v8.h>
 
 namespace WebCore {
 
-typedef Vector<MicrotaskCallback> MicrotaskQueue;
-
-static MicrotaskQueue& microtaskQueue()
-{
-    DEFINE_STATIC_LOCAL(MicrotaskQueue, microtaskQueue, ());
-    return microtaskQueue;
-}
-
 void Microtask::performCheckpoint()
 {
-    V8PerIsolateData* isolateData = V8PerIsolateData::current();
+    v8::Isolate* isolate = v8::Isolate::GetCurrent();
+    V8PerIsolateData* isolateData = V8PerIsolateData::from(isolate);
     ASSERT(isolateData);
     if (isolateData->performingMicrotaskCheckpoint())
         return;
     isolateData->setPerformingMicrotaskCheckpoint(true);
 
-    while (!microtaskQueue().isEmpty()) {
-        Vector<MicrotaskCallback> microtasks;
-        microtasks.swap(microtaskQueue());
-        for (size_t i = 0; i < microtasks.size(); ++i) {
-            microtasks[i]();
-        }
-    }
+    v8::HandleScope handleScope(isolate);
+    v8::Local<v8::Context> context = isolateData->ensureDomInJSContext();
+    v8::Context::Scope scope(context);
+    v8::V8::RunMicrotasks(isolate);
 
     isolateData->setPerformingMicrotaskCheckpoint(false);
 }
 

[adamk, 2014/02/14 22:26:37]

Please add a COMPILE_ASSERT that sizeof void* == sizeof MicrotaskCallback

Jeffrey suggests that that'll be sufficient to make this safe.

[rafaelw, 2014/02/14 22:52:51]

Done.

+static void microtaskFunctionCallback(const v8::FunctionCallbackInfo<v8::Value>& info)
+{
+    MicrotaskCallback callback =
+        reinterpret_cast<MicrotaskCallback>(reinterpret_cast<intptr_t>(

[adamk, 2014/02/14 21:33:46]

This just looks worse and worse to me the more I see it. I'd like to
better-understand the C++ rule about void* and function callbacks before giving
this the OK in Blink. I'm going to see who I can rustle up (either ajwong or
jyasskin).

FWIW, here's what Chromium's base::Callback system has to say about this:

  // In C++, it is safe to cast function pointers to function pointers of
  // another type. It is not okay to use void*. We create a InvokeFuncStorage
  // that that can store our function pointer, and then cast it back to
  // the original type on usage.
  typedef void(*InvokeFuncStorage)(void);

I'm wondering if we could just get away with adding a new v8 type that does
something like this.

+            info.Data().As<v8::External>()->Value()));
+    (*callback)();
+}
+
 void Microtask::enqueueMicrotask(MicrotaskCallback callback)
 {
-    microtaskQueue().append(callback);
+    v8::Isolate* isolate = v8::Isolate::GetCurrent();
+    V8PerIsolateData* isolateData = V8PerIsolateData::from(isolate);
+    v8::HandleScope handleScope(isolate);
+    v8::Local<v8::Context> context = isolateData->ensureDomInJSContext();
+    v8::Context::Scope scope(context);
+    v8::Local<v8::External> handler =
+        v8::External::New(isolate,
+            reinterpret_cast<void*>(reinterpret_cast<intptr_t>(callback)));
+    v8::V8::EnqueueMicrotask(isolate, v8::Function::New(isolate, &microtaskFunctionCallback, handler));
 }
 
 } // namespace WebCore