82 lines
3.0 KiB
C
82 lines
3.0 KiB
C
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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
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#define BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
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#include <dispatch/dispatch.h>
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#include "base/single_thread_task_runner.h"
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#include "base/synchronization/waitable_event.h"
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namespace base {
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namespace mac {
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// This is an implementation of the TaskRunner interface that runs closures on
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// a thread managed by Apple's libdispatch. This has the benefit of being able
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// to PostTask() and friends to a dispatch queue, while being reusable as a
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// dispatch_queue_t.
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//
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// One would use this class if an object lives exclusively on one thread but
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// needs a dispatch_queue_t for use in a system API. This ensures all dispatch
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// callbacks happen on the same thread as Closure tasks.
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//
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// A LibDispatchTaskRunner will continue to run until all references to the
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// underlying dispatch queue are released.
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//
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// Important Notes:
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// - There is no MessageLoop running on this thread, and ::current() returns
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// NULL.
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// - No nested loops can be run, and all tasks are run non-nested.
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// - Work scheduled via libdispatch runs at the same priority as and is
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// interleaved with posted tasks, though FIFO order is guaranteed.
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//
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class BASE_EXPORT LibDispatchTaskRunner : public base::SingleThreadTaskRunner {
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public:
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// Starts a new serial dispatch queue with a given name.
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explicit LibDispatchTaskRunner(const char* name);
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// base::TaskRunner:
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virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
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const Closure& task,
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base::TimeDelta delay) OVERRIDE;
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virtual bool RunsTasksOnCurrentThread() const OVERRIDE;
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// base::SequencedTaskRunner:
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virtual bool PostNonNestableDelayedTask(
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const tracked_objects::Location& from_here,
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const Closure& task,
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base::TimeDelta delay) OVERRIDE;
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// This blocks the calling thread until all work on the dispatch queue has
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// been run and the queue has been destroyed. Destroying a queue requires
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// ALL retained references to it to be released. Any new tasks posted to
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// this thread after shutdown are dropped.
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void Shutdown();
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// Returns the dispatch queue associated with this task runner, for use with
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// system APIs that take dispatch queues. The caller is responsible for
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// retaining the result.
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//
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// All properties (context, finalizer, etc.) are managed by this class, and
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// clients should only use the result of this for dispatch_async().
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dispatch_queue_t GetDispatchQueue() const;
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protected:
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virtual ~LibDispatchTaskRunner();
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private:
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static void Finalizer(void* context);
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dispatch_queue_t queue_;
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// The event on which Shutdown waits until Finalizer runs.
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base::WaitableEvent queue_finalized_;
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};
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} // namespace mac
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} // namespace base
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#endif // BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
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