compositor-worker: Share a thread and an isolate for compositor workers.

Source/modules/compositorworker/CompositorWorkerManager.cpp

Index: Source/modules/compositorworker/CompositorWorkerManager.cpp
diff --git a/Source/modules/compositorworker/CompositorWorkerManager.cpp b/Source/modules/compositorworker/CompositorWorkerManager.cpp
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index 0000000000000000000000000000000000000000..bf77e265f9d4069814e4b619f7da8465daa9785f
--- /dev/null
+++ b/Source/modules/compositorworker/CompositorWorkerManager.cpp
@@ -0,0 +1,145 @@
+// Copyright 2015 The Chromium 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 "config.h"
+#include "modules/compositorworker/CompositorWorkerManager.h"
+
+#include "bindings/core/v8/V8Binding.h"
+#include "bindings/core/v8/V8GCController.h"
+#include "bindings/core/v8/V8Initializer.h"
+#include "bindings/core/v8/V8PerIsolateData.h"
+#include "platform/ThreadSafeFunctional.h"
+#include "platform/WebThreadSupportingGC.h"
+#include "wtf/MainThread.h"
+#include "wtf/ThreadingPrimitives.h"
+
+namespace blink {
+
+namespace {
+
+static CompositorWorkerManager* s_instance = nullptr;
+
+static Mutex& singletonMutex()
+{
+    AtomicallyInitializedStaticReference(Mutex, mutex, new Mutex);
+    return mutex;
+}
+
+static void destroyThread(WebThreadSupportingGC* thread)
+{
+    delete thread;
+}
+
+} // namespace
+
+void CompositorWorkerManager::initialize()
+{
+    MutexLocker lock(singletonMutex());
+    ASSERT(!s_instance);
+    s_instance = new CompositorWorkerManager();
+}
+
+void CompositorWorkerManager::shutdown()
+{
+    MutexLocker lock(singletonMutex());
+    ASSERT(s_instance);
+    delete s_instance;
+    s_instance = nullptr;
+}
+
+CompositorWorkerManager* CompositorWorkerManager::instance()
+{
+    MutexLocker lock(singletonMutex());
+    ASSERT(s_instance);
+    return s_instance;
+}
+
+CompositorWorkerManager::CompositorWorkerManager()
+{
+}
+
+CompositorWorkerManager::~CompositorWorkerManager()
+{
+}
+
+WebThreadSupportingGC& CompositorWorkerManager::compositorWorkerThread()
+{
+    MutexLocker lock(m_mutex);
+    if (!m_thread) {
+        ASSERT(isMainThread());
+        ASSERT(!m_workerCount);
+        m_thread = WebThreadSupportingGC::create("CompositorWorker Thread");
+    }
+    return *m_thread.get();
+}
+
+void CompositorWorkerManager::initializeBackingThread()
+{
+    ASSERT(m_thread->isCurrentThread());
+    MutexLocker lock(m_mutex);
+    ++m_workerCount;
+    if (m_workerCount == 1)
+        m_thread->initialize();
+}
+
+void CompositorWorkerManager::shutdownBackingThread()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    ASSERT(m_workerCount > 0);
+    --m_workerCount;
+    if (m_workerCount == 0) {
+        m_thread->shutdown();
+        Platform::current()->mainThread()->postTask(FROM_HERE, threadSafeBind(destroyThread, AllowCrossThreadAccess(m_thread.leakPtr())));
+    }
+}
+
+v8::Isolate* CompositorWorkerManager::initializedIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    if (!m_isolate) {
+        m_isolate = V8PerIsolateData::initialize();

[haraken, 2015/06/03 02:44:11]

Can we do the isolate initialization in initializeBackingThread()?

[sadrul, 2015/06/03 03:16:00]

Done.

+        V8Initializer::initializeWorker(m_isolate);
+
+        m_interruptor = adoptPtr(new V8IsolateInterruptor(m_isolate));
+        ThreadState::current()->addInterruptor(m_interruptor.get());
+        ThreadState::current()->registerTraceDOMWrappers(m_isolate, V8GCController::traceDOMWrappers);
+    }
+    // It is safe to use the existing isolate even if TerminateExecution() has been
+    // called on it, without calling CancelTerminateExecution().
+    return m_isolate;
+}
+
+void CompositorWorkerManager::willDestroyIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    if (m_workerCount == 1) {
+        V8PerIsolateData::willBeDestroyed(m_isolate);
+        ThreadState::current()->removeInterruptor(m_interruptor.get());
+    }
+}
+
+void CompositorWorkerManager::destroyIsolate()
+{
+    MutexLocker lock(m_mutex);
+    if (!m_thread) {

[haraken, 2015/06/03 02:44:11]

What is this check for? Is it possible that m_thread becomes nullptr (after
we've initialized it)?

I guess you need to either of:

- Do m_thread=nullptr after calling m_thread->shutdown().
- Change the check to if(m_workerCount == 0).

[sadrul, 2015/06/03 03:16:00]

After calling m_thread->shutdown(), we schedule the thread to be destroyed in a
posted task in the main-thread. We pass the thread ownership to the callback by
calling leakPtr() on it (like 94), which does reset it back to nullptr. But I
have added code in there to do this explicitly too.

+        ASSERT(m_workerCount == 0);
+        V8PerIsolateData::destroy(m_isolate);
+        m_isolate = nullptr;
+    }
+}
+
+void CompositorWorkerManager::terminateIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(isMainThread());
+    if (m_workerCount > 1)
+        return;
+
+    v8::V8::TerminateExecution(m_isolate);
+}
+
+} // namespace blink