Make new TaskRunner, SequencedTaskRunner, and SingleThreadTaskRunner interfaces

base/task_runner.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/task_runner.h"
+
+#include "base/compiler_specific.h"
+#include "base/threading/post_task_and_reply_impl.h"
+
+namespace base {
+
+namespace {
+
+// TODO(akalin): There's only one other implementation of
+// PostTaskAndReplyImpl in WorkerPool.  Investigate whether it'll be
+// possible to merge the two.
+class PostTaskAndReplyTaskRunner : public internal::PostTaskAndReplyImpl {
+ public:
+  PostTaskAndReplyTaskRunner(TaskRunner* destination);
+
+ private:
+  virtual bool PostTask(const tracked_objects::Location& from_here,
+                        const Closure& task) OVERRIDE;
+
+  // Non-owning.

[willchan no longer on Chromium, 2012/02/09 20:50:50]

Sorry, I'm tired. Why is it OK for this to be non-owning? Shouldn't it be a
scoped_refptr?

[akalin, 2012/02/10 22:48:59]

This class is essentially just to define a PostTask.  In PostTaskAndReply, this
class is created, PostTaskAndReply is called, then the object is immediately
destroyed.

+  TaskRunner* destination_;
+};
+
+PostTaskAndReplyTaskRunner::PostTaskAndReplyTaskRunner(
+    TaskRunner* destination) : destination_(destination) {}

[willchan no longer on Chromium, 2012/02/09 20:50:50]

DCHECK early on that it's non-NULL.

[akalin, 2012/02/10 22:48:59]

Done.

+
+bool PostTaskAndReplyTaskRunner::PostTask(
+    const tracked_objects::Location& from_here,
+    const Closure& task) {
+  return destination_->PostTask(from_here, task);
+}
+
+}  // namespace
+
+bool TaskRunner::PostTaskAndReply(
+    const tracked_objects::Location& from_here,
+    const Closure& task,
+    const Closure& reply) {
+  return PostTaskAndReplyTaskRunner(this).PostTaskAndReply(
+      from_here, task, reply);
+}
+
+TaskRunner::TaskRunner() {}
+
+TaskRunner::~TaskRunner() {}
+
+void TaskRunner::OnDestruct() const {
+  delete this;
+}
+
+void TaskRunnerTraits::Destruct(const TaskRunner* task_runner) {
+  task_runner->OnDestruct();
+}
+
+}  // namespace base