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83 lines
2.6 KiB
C
83 lines
2.6 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 NET_DNS_SERIAL_WORKER_H_
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#define NET_DNS_SERIAL_WORKER_H_
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#include <string>
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#include "base/compiler_specific.h"
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#include "base/macros.h"
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#include "base/memory/ref_counted.h"
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#include "base/sequence_checker.h"
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#include "base/task_scheduler/task_traits.h"
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#include "net/base/net_export.h"
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namespace net {
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// SerialWorker executes a job on TaskScheduler serially -- **once at a time**.
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// On |WorkNow|, a call to |DoWork| is scheduled on TaskScheduler. Once it
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// completes, |OnWorkFinished| is called on the origin thread. If |WorkNow| is
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// called (1 or more times) while |DoWork| is already under way, |DoWork| will
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// be called once: after current |DoWork| completes, before a call to
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// |OnWorkFinished|.
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//
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// This behavior is designed for updating a result after some trigger, for
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// example reading a file once FilePathWatcher indicates it changed.
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//
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// Derived classes should store results of work done in |DoWork| in dedicated
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// fields and read them in |OnWorkFinished| which is executed on the origin
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// thread. This avoids the need to template this class.
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//
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// This implementation avoids locking by using the |state_| member to ensure
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// that |DoWork| and |OnWorkFinished| cannot execute in parallel.
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class NET_EXPORT_PRIVATE SerialWorker
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: public base::RefCountedThreadSafe<SerialWorker> {
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public:
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SerialWorker();
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// Unless already scheduled, post |DoWork| to TaskScheduler.
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// Made virtual to allow mocking.
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virtual void WorkNow();
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// Stop scheduling jobs.
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void Cancel();
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bool IsCancelled() const { return state_ == CANCELLED; }
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protected:
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friend class base::RefCountedThreadSafe<SerialWorker>;
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// protected to allow sub-classing, but prevent deleting
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virtual ~SerialWorker();
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// Executed on TaskScheduler, at most once at a time.
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virtual void DoWork() = 0;
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// Executed on origin thread after |DoRead| completes.
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virtual void OnWorkFinished() = 0;
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// Used to verify that the constructor, WorkNow(), Cancel() and
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// OnWorkJobFinished() are called on the same sequence.
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SEQUENCE_CHECKER(sequence_checker_);
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private:
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enum State {
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CANCELLED = -1,
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IDLE = 0,
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WORKING, // |DoWorkJob| posted to TaskScheduler, until |OnWorkJobFinished|
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PENDING, // |WorkNow| while WORKING, must re-do work
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};
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// Called on the the origin thread after |DoWork| completes.
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void OnWorkJobFinished();
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State state_;
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DISALLOW_COPY_AND_ASSIGN(SerialWorker);
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};
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} // namespace net
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#endif // NET_DNS_SERIAL_WORKER_H_
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