// 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.
#ifndef BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
#define BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
#include <dispatch/dispatch.h>
#include "base/single_thread_task_runner.h"
#include "base/synchronization/waitable_event.h"
namespace base {
namespace mac {
// This is an implementation of the TaskRunner interface that runs closures on
// a thread managed by Apple's libdispatch. This has the benefit of being able
// to PostTask() and friends to a dispatch queue, while being reusable as a
// dispatch_queue_t.
//
// One would use this class if an object lives exclusively on one thread but
// needs a dispatch_queue_t for use in a system API. This ensures all dispatch
// callbacks happen on the same thread as Closure tasks.
//
// A LibDispatchTaskRunner will continue to run until all references to the
// underlying dispatch queue are released.
//
// Important Notes:
// - There is no MessageLoop running on this thread, and ::current() returns
// NULL.
// - No nested loops can be run, and all tasks are run non-nested.
// - Work scheduled via libdispatch runs at the same priority as and is
// interleaved with posted tasks, though FIFO order is guaranteed.
//
class BASE_EXPORT LibDispatchTaskRunner : public base::SingleThreadTaskRunner {
public:
// Starts a new serial dispatch queue with a given name.
explicit LibDispatchTaskRunner(const char* name);
// base::TaskRunner:
virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
const Closure& task,
base::TimeDelta delay) OVERRIDE;
virtual bool RunsTasksOnCurrentThread() const OVERRIDE;
// base::SequencedTaskRunner:
virtual bool PostNonNestableDelayedTask(
const tracked_objects::Location& from_here,
const Closure& task,
base::TimeDelta delay) OVERRIDE;
// This blocks the calling thread until all work on the dispatch queue has
// been run and the queue has been destroyed. Destroying a queue requires
// ALL retained references to it to be released. Any new tasks posted to
// this thread after shutdown are dropped.
void Shutdown();
// Returns the dispatch queue associated with this task runner, for use with
// system APIs that take dispatch queues. The caller is responsible for
// retaining the result.
//
// All properties (context, finalizer, etc.) are managed by this class, and
// clients should only use the result of this for dispatch_async().
dispatch_queue_t GetDispatchQueue() const;
protected:
virtual ~LibDispatchTaskRunner();
private:
static void Finalizer(void* context);
dispatch_queue_t queue_;
// The event on which Shutdown waits until Finalizer runs.
base::WaitableEvent queue_finalized_;
};
} // namespace mac
} // namespace base
#endif // BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_