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 WorkerV8Isolate {
+    WTF_MAKE_NONCOPYABLE(SharedV8Isolate);
+public:
+    explicit SharedV8Isolate(v8::Isolate* isolate)
+        : m_isolate(isolate) { }
+    ~SharedV8Isolate() override
+    {
+        CompositorWorkerManager::instance()->destroyIsolate();
+    }
+
+private:
+    // WorkerV8Isolate:
+    v8::Isolate* isolate() const override { return m_isolate; }
+    void willDestroy() override
+    {
+        CompositorWorkerManager::instance()->willDestroyIsolate();
+    }
+
+    void terminateExecution() override
+    {
+        CompositorWorkerManager::instance()->terminateIsolate();
+    }
+
+    v8::Isolate* m_isolate;
+};
+
+} // namespace
+
+static CompositorWorkerManager* s_instance = nullptr;

[kinuko, 2015/05/26 14:41:25]

Hmm, so we want to have single manager per process, no matter how many
contexts/documents we have... is it the intention?  (Do you mind briefing the
reason why the model is chosen?)

[sadrul, 2015/05/27 01:28:00]

That is indeed the intention, at least for now.

There is only a single compositor-thread per renderer process. So it is
reasonable to have a single worker-thread that communicates with the
compositor-thread. We do have opportunities here to experiment with allowing
each page to have its own thread for compositor-workers though. But we would
like to go with the simpler solution at first.

+
+static Mutex& singletonMutex()
+{
+    AtomicallyInitializedStaticReference(Mutex, mutex, new Mutex);
+    return mutex;
+}
+
+void CompositorWorkerManager::initialize()
+{
+    MutexLocker lock(singletonMutex());
+    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()
+{
+    if (m_isolate)
+        ASSERT(m_isolate.leakPtr());
+}
+
+WebThreadSupportingGC& CompositorWorkerManager::compositorWorkerThread()
+{
+    MutexLocker lock(m_mutex);
+    if (!m_thread) {
+        ASSERT(isMainThread());
+        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();
+}
+
+static void destroyThread(WebThreadSupportingGC* thread)
+{
+    delete thread;
+}

[kinuko, 2015/05/26 14:41:25]

nit: moving these static local methods in the anon namespace?

[sadrul, 2015/05/27 01:28:00]

Done.

+
+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<WorkerV8Isolate> CompositorWorkerManager::createIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    if (!m_isolate)
+        m_isolate = WorkerV8Isolate::createDefault();
+    ++m_isolateCount;
+    return adoptPtr(new SharedV8Isolate(m_isolate->isolate()));
+}
+
+void CompositorWorkerManager::willDestroyIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(m_thread->isCurrentThread());
+    --m_isolateCount;
+    if (m_isolateCount == 0)
+        m_isolate->willDestroy();
+}
+
+void CompositorWorkerManager::destroyIsolate()
+{
+    MutexLocker lock(m_mutex);
+    if (m_isolateCount == 0)
+        m_isolate = nullptr;
+}
+
+void CompositorWorkerManager::terminateIsolate()
+{
+    MutexLocker lock(m_mutex);
+    ASSERT(isMainThread());
+    if (m_isolateCount > 1)
+        return;
+
+    m_isolate->terminateExecution();
+    // TODO(sad): Reset |m_isolate| here, so that if another script is created before this one is destroyed,
+    // we would end up trying to reuse this terminated isolate.
+}
+
+} // namespace blink