chrome/browser/history/history_db_task.h

// Copyright 2013 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 CHROME_BROWSER_HISTORY_HISTORY_DB_TASK_H_
#define CHROME_BROWSER_HISTORY_HISTORY_DB_TASK_H_

#include "base/memory/ref_counted.h"

namespace history {

class HistoryBackend;
class HistoryDatabase;

// HistoryDBTask can be used to process arbitrary work on the history backend
// thread. HistoryDBTask is scheduled using HistoryService::ScheduleDBTask.
// When HistoryBackend processes the task it invokes RunOnDBThread. Once the
// task completes and has not been canceled, DoneRunOnMainThread is invoked back
// on the main thread.
class HistoryDBTask : public base::RefCountedThreadSafe<HistoryDBTask> {
 public:
  // Invoked on the database thread. The return value indicates whether the
  // task is done. A return value of true signals the task is done and
  // RunOnDBThread should NOT be invoked again. A return value of false
  // indicates the task is not done, and should be run again after other
  // tasks are given a chance to be processed.
  virtual bool RunOnDBThread(HistoryBackend* backend, HistoryDatabase* db) = 0;

  // Invoked on the main thread once RunOnDBThread has returned true. This is
  // only invoked if the request was not canceled and returned true from
  // RunOnDBThread.
  virtual void DoneRunOnMainThread() = 0;

 protected:
  friend class base::RefCountedThreadSafe<HistoryDBTask>;

  virtual ~HistoryDBTask() {}
};

}  // namespace history

#endif  // CHROME_BROWSER_HISTORY_HISTORY_DB_TASK_H_