Add base::ThreadTaskRunner class.

base/thread_task_runner_handle.cc

+// Copyright (c) 2012 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 "base/thread_task_runner_handle.h"
+
+#include "base/lazy_instance.h"
+#include "base/single_thread_task_runner.h"
+#include "base/threading/thread_local.h"
+
+namespace base {
+
+namespace {
+
+base::LazyInstance<base::ThreadLocalPointer<ThreadTaskRunnerHandle> >
+    lazy_tls_ptr = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+// static
+scoped_refptr<SingleThreadTaskRunner> ThreadTaskRunnerHandle::Get() {
+  ThreadTaskRunnerHandle* current = lazy_tls_ptr.Pointer()->Get();
+  DCHECK(current);
+  return current->task_runner_;
+}
+
+ThreadTaskRunnerHandle::ThreadTaskRunnerHandle(
+    const scoped_refptr<SingleThreadTaskRunner>& task_runner)
+    : task_runner_(task_runner) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(!lazy_tls_ptr.Pointer()->Get());
+  lazy_tls_ptr.Pointer()->Set(this);
+}
+
+ThreadTaskRunnerHandle::~ThreadTaskRunnerHandle() {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK_EQ(lazy_tls_ptr.Pointer()->Get(), this);
+  lazy_tls_ptr.Pointer()->Set(NULL);
+}
+
+}  // namespace base