Create LibDispatchTaskRunner, a SingleThreadTaskRunner that is backed by a libdispatch queue.

base/mac/libdispatch_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/mac/libdispatch_task_runner.h"
+
+#include "base/callback.h"
+
+namespace base {
+namespace mac {
+
+LibDispatchTaskRunner::LibDispatchTaskRunner(const char* name)
+    : queue_(dispatch_queue_create(name, NULL)) {
+}
+
+bool LibDispatchTaskRunner::PostDelayedTask(
+    const tracked_objects::Location& from_here,
+    const Closure& task,
+    base::TimeDelta delay) {
+  if (!queue_)
+    return false;
+
+  // The block runtime would implicitly copy the reference, not the object
+  // it's referencing. Copy the closure into block storage so it's available
+  // to run.
+  __block const Closure task_copy = task;
+  void(^run_task)(void) = ^{
+      task_copy.Run();
+  };
+
+  int64 delay_nano =
+      delay.InMicroseconds() * base::Time::kNanosecondsPerMicrosecond;
+  if (delay_nano > 0) {
+    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, delay_nano);
+    dispatch_after(time, queue_, run_task);
+  } else {
+    dispatch_async(queue_, run_task);
+  }
+  return true;
+}
+
+bool LibDispatchTaskRunner::RunsTasksOnCurrentThread() const {
+  return queue_ == dispatch_get_current_queue();
+}
+
+bool LibDispatchTaskRunner::PostNonNestableDelayedTask(
+    const tracked_objects::Location& from_here,
+    const Closure& task,
+    base::TimeDelta delay) {
+  return PostDelayedTask(from_here, task, delay);
+}
+
+dispatch_queue_t LibDispatchTaskRunner::GetDispatchQueue() const {
+  return queue_;
+}
+
+LibDispatchTaskRunner::~LibDispatchTaskRunner() {
+  dispatch_release(queue_);
+}
+
+}  // namespace mac
+}  // namespace base