net/dns/serial_worker.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef NET_DNS_SERIAL_WORKER_H_
   6 #define NET_DNS_SERIAL_WORKER_H_
   7
   8 #include <string>
   9
  10 #include "base/compiler_specific.h"
  11 #include "base/memory/ref_counted.h"
  12 #include "net/base/net_export.h"
  13
  14 // Forward declaration
  15 namespace base {
  16 class MessageLoopProxy;
  17 }
  18
  19 namespace net {
  20
  21 // SerialWorker executes a job on WorkerPool serially -- **once at a time**.
  22 // On |WorkNow|, a call to |DoWork| is scheduled on the WorkerPool. Once it
  23 // completes, |OnWorkFinished| is called on the origin thread.
  24 // If |WorkNow| is called (1 or more times) while |DoWork| is already under way,
  25 // |DoWork| will be called once: after current |DoWork| completes, before a
  26 // call to |OnWorkFinished|.
  27 //
  28 // This behavior is designed for updating a result after some trigger, for
  29 // example reading a file once FilePathWatcher indicates it changed.
  30 //
  31 // Derived classes should store results of work done in |DoWork| in dedicated
  32 // fields and read them in |OnWorkFinished| which is executed on the origin
  33 // thread. This avoids the need to template this class.
  34 //
  35 // This implementation avoids locking by using the |state_| member to ensure
  36 // that |DoWork| and |OnWorkFinished| cannot execute in parallel.
  37 //
  38 // TODO(szym): update to WorkerPool::PostTaskAndReply once available.
  39 class NET_EXPORT_PRIVATE SerialWorker
  40   : NON_EXPORTED_BASE(public base::RefCountedThreadSafe<SerialWorker>) {
  41  public:
  42   SerialWorker();
  43
  44   // Unless already scheduled, post |DoWork| to WorkerPool.
  45   // Made virtual to allow mocking.
  46   virtual void WorkNow();
  47
  48   // Stop scheduling jobs.
  49   void Cancel();
  50
  51   bool IsCancelled() const { return state_ == CANCELLED; }
  52
  53  protected:
  54   friend class base::RefCountedThreadSafe<SerialWorker>;
  55   // protected to allow sub-classing, but prevent deleting
  56   virtual ~SerialWorker();
  57
  58   // Executed on WorkerPool, at most once at a time.
  59   virtual void DoWork() = 0;
  60
  61   // Executed on origin thread after |DoRead| completes.
  62   virtual void OnWorkFinished() = 0;
  63
  64   base::MessageLoopProxy* loop() { return message_loop_.get(); }
  65
  66  private:
  67   enum State {
  68     CANCELLED = -1,
  69     IDLE = 0,
  70     WORKING,  // |DoWorkJob| posted on WorkerPool, until |OnWorkJobFinished|
  71     PENDING,  // |WorkNow| while WORKING, must re-do work
  72     WAITING,  // WorkerPool is busy, |RetryWork| is posted
  73   };
  74
  75   // Called on the worker thread, executes |DoWork| and notifies the origin
  76   // thread.
  77   void DoWorkJob();
  78
  79   // Called on the the origin thread after |DoWork| completes.
  80   void OnWorkJobFinished();
  81
  82   // Posted to message loop in case WorkerPool is busy. (state == WAITING)
  83   void RetryWork();
  84
  85   // Message loop for the thread of origin.
  86   scoped_refptr<base::MessageLoopProxy> message_loop_;
  87
  88   State state_;
  89
  90   DISALLOW_COPY_AND_ASSIGN(SerialWorker);
  91 };
  92
  93 }  // namespace net
  94
  95 #endif  // NET_DNS_SERIAL_WORKER_H_
  96