Refactoring WorkletThreadBackingHolder with template pattern

third_party/WebKit/Source/core/workers/WorkletThreadHolder.h

Index: third_party/WebKit/Source/core/workers/WorkletThreadHolder.h
diff --git a/third_party/WebKit/Source/core/workers/WorkletThreadHolder.h b/third_party/WebKit/Source/core/workers/WorkletThreadHolder.h
new file mode 100644
index 0000000000000000000000000000000000000000..0f8c2a907f43c4889b45c813431c2a6ccb6f7fbf
--- /dev/null
+++ b/third_party/WebKit/Source/core/workers/WorkletThreadHolder.h
@@ -0,0 +1,128 @@
+// Copyright 2016 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.
+
+#ifndef WorkletThreadHolder_h
+#define WorkletThreadHolder_h
+
+#include "core/CoreExport.h"
+#include "core/workers/WorkerBackingThread.h"
+#include "platform/WaitableEvent.h"
+#include "platform/WebThreadSupportingGC.h"
+#include "wtf/PtrUtil.h"
+
+namespace blink {
+
+// WorkletThreadHolder is a template class which is designed for singleton
+// instance of DerivedWorkletThread (i.e. AnimationWorkletThread,
+// AudioWorkletThread).
+template <class DerivedWorkletThread>
+class WorkletThreadHolder {
+ public:
+  static WorkletThreadHolder<DerivedWorkletThread>* threadHolderInstance() {
+    MutexLocker locker(holderInstanceMutex());
+    return s_threadHolderInstance;
+  }
+
+  static void ensureInstance(const char* threadName,
+                             BlinkGC::ThreadHeapMode threadHeapMode) {
+    DCHECK(isMainThread());
+    MutexLocker locker(holderInstanceMutex());
+    if (s_threadHolderInstance)
+      return;
+    s_threadHolderInstance = new WorkletThreadHolder<DerivedWorkletThread>;
+    s_threadHolderInstance->initialize(
+        WorkerBackingThread::create(threadName, threadHeapMode));
+  }
+
+  static void ensureInstance(WebThread* thread) {
+    DCHECK(isMainThread());
+    MutexLocker locker(holderInstanceMutex());
+    if (s_threadHolderInstance)
+      return;
+    s_threadHolderInstance = new WorkletThreadHolder<DerivedWorkletThread>;
+    s_threadHolderInstance->initialize(WorkerBackingThread::create(thread));
+  }
+
+  static void createForTest(const char* threadName,
+                            BlinkGC::ThreadHeapMode threadHeapMode) {
+    MutexLocker locker(holderInstanceMutex());
+    DCHECK(!s_threadHolderInstance);
+    s_threadHolderInstance = new WorkletThreadHolder<DerivedWorkletThread>;
+    s_threadHolderInstance->initialize(
+        WorkerBackingThread::createForTest(threadName, threadHeapMode));
+  }
+
+  static void createForTest(WebThread* thread) {
+    MutexLocker locker(holderInstanceMutex());
+    DCHECK(!s_threadHolderInstance);
+    s_threadHolderInstance = new WorkletThreadHolder<DerivedWorkletThread>;
+    s_threadHolderInstance->initialize(
+        WorkerBackingThread::createForTest(thread));
+  }
+
+  static void clearInstance() {
+    DCHECK(isMainThread());
+    MutexLocker locker(holderInstanceMutex());
+    if (s_threadHolderInstance) {
+      s_threadHolderInstance->shutdownAndWait();
+      delete s_threadHolderInstance;
+      s_threadHolderInstance = nullptr;
+    }
+  }
+
+  WorkerBackingThread* thread() { return m_thread.get(); }
+
+ private:
+  WorkletThreadHolder() {}
+  ~WorkletThreadHolder() {}
+
+  static Mutex& holderInstanceMutex() {
+    DEFINE_THREAD_SAFE_STATIC_LOCAL(Mutex, holderMutex, new Mutex);
+    return holderMutex;
+  }
+
+  void initialize(std::unique_ptr<WorkerBackingThread> backingThread) {
+    m_thread = std::move(backingThread);
+    m_thread->backingThread().postTask(
+        BLINK_FROM_HERE,
+        crossThreadBind(&WorkletThreadHolder::initializeOnWorkletThread,
+                        crossThreadUnretained(this)));
+  }
+
+  void initializeOnWorkletThread() {
+    MutexLocker locker(holderInstanceMutex());
+    DCHECK(!m_initialized);
+    m_thread->initialize();
+    m_initialized = true;
+  }
+
+  void shutdownAndWait() {
+    DCHECK(isMainThread());
+    WaitableEvent waitableEvent;
+    m_thread->backingThread().postTask(
+        BLINK_FROM_HERE,
+        crossThreadBind(&WorkletThreadHolder::shutdownOnWorlketThread,
+                        crossThreadUnretained(this),
+                        crossThreadUnretained(&waitableEvent)));
+    waitableEvent.wait();
+  }
+
+  void shutdownOnWorlketThread(WaitableEvent* waitableEvent) {
+    m_thread->shutdown();
+    waitableEvent->signal();
+  }
+
+  std::unique_ptr<WorkerBackingThread> m_thread;
+  bool m_initialized = false;
+
+  static WorkletThreadHolder<DerivedWorkletThread>* s_threadHolderInstance;
+};
+
+template <class DerivedWorkletThread>
+WorkletThreadHolder<DerivedWorkletThread>*
+    WorkletThreadHolder<DerivedWorkletThread>::s_threadHolderInstance = nullptr;
+
+}  // namespace blink
+
+#endif  // WorkletBackingThreadHolder_h