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

Source/modules/compositorworker/CompositorWorkerManager.cpp

+// 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 "platform/ThreadSafeFunctional.h"
+#include "platform/WebThreadSupportingGC.h"
+#include "wtf/MainThread.h"
+#include "wtf/ThreadingPrimitives.h"
+
+namespace blink {
+
+namespace {
+
+class SharedV8Isolate final : public WorkerIsolateWrapper {
+    WTF_MAKE_NONCOPYABLE(SharedV8Isolate);
+public:
+    explicit SharedV8Isolate(v8::Isolate* isolate)
+        : m_isolate(isolate) { }
+    ~SharedV8Isolate() override
+    {
+        CompositorWorkerManager::instance()->destroyIsolate();
+    }
+
+private:
+    // WorkerIsolateWrapper:
+    v8::Isolate* isolate() const override { return m_isolate; }
+    void willDestroy() override
+    {
+        CompositorWorkerManager::instance()->willDestroyIsolate();
+    }
+
+    void terminateExecution() override
+    {
+        CompositorWorkerManager::instance()->terminateIsolate();
+    }
+
+    v8::Isolate* m_isolate;
+};
+
+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());
+    if (s_instance)

[kinuko, 2015/06/01 13:15:42]

nit: could this be null?

[sadrul, 2015/06/01 14:21:16]

We initialize conditionally on whether the feature is turned on or not. We do
not check that condition during shutdown() (in InitModules.cpp). Maybe I should
do that instead?

... Done.

+        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())));
+    }
+}
+
+PassOwnPtr<WorkerIsolateWrapper> CompositorWorkerManager::createIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    if (!m_isolate)
+        m_isolate = WorkerIsolateWrapper::createDefault();
+    else if (m_isolate->isolate()->IsExecutionTerminating())
+        m_isolate->isolate()->CancelTerminateExecution();

[kinuko, 2015/06/01 13:15:42]

Was looking a recent bug that explains a bit about CancelTerminateExecution...
is that really what we want to do here (i.e. stopping to tear down the current
v8 stack frames)?

https://code.google.com/p/chromium/issues/detail?id=462698

[sadrul, 2015/06/01 14:21:16]

Whoa. Thanks a lot for that link! Very informative. It looks like I did
misunderstand the API as the OP on the bug, and it is not actually necessary to
cancel-termination here. The unit-tests verify that the isolate is able to
accommodate new workers. I have removed this, and added a comment for
explanation.

+    return adoptPtr(new SharedV8Isolate(m_isolate->isolate()));
+}
+
+void CompositorWorkerManager::willDestroyIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    if (m_workerCount == 1)
+        m_isolate->willDestroy();
+}
+
+void CompositorWorkerManager::destroyIsolate()
+{
+    MutexLocker lock(m_mutex);
+    if (!m_thread)
+        m_isolate.clear();

[kinuko, 2015/06/01 13:15:42]

Can you also assert m_workerCount == 0 here?

[sadrul, 2015/06/01 14:21:16]

Done.

+}
+
+void CompositorWorkerManager::terminateIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(isMainThread());
+    if (m_workerCount > 1)
+        return;
+
+    m_isolate->terminateExecution();
+}
+
+} // namespace blink