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      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 BASE_IOS_SCOPED_CRITICAL_ACTION_H_
      6 #define BASE_IOS_SCOPED_CRITICAL_ACTION_H_
      7 
      8 #include "base/memory/ref_counted.h"
      9 #include "base/synchronization/lock.h"
     10 
     11 namespace base {
     12 namespace ios {
     13 
     14 // This class attempts to allow the application to continue to run for a period
     15 // of time after it transitions to the background. The construction of an
     16 // instance of this class marks the beginning of a task that needs background
     17 // running time when the application is moved to the background and the
     18 // destruction marks the end of such a task.
     19 //
     20 // Note there is no guarantee that the task will continue to finish when the
     21 // application is moved to the background.
     22 //
     23 // This class should be used at times where leaving a task unfinished might be
     24 // detrimental to user experience. For example, it should be used to ensure that
     25 // the application has enough time to save important data or at least attempt to
     26 // save such data.
     27 class ScopedCriticalAction {
     28  public:
     29   ScopedCriticalAction();
     30   ~ScopedCriticalAction();
     31 
     32  private:
     33   // Core logic; ScopedCriticalAction should not be reference counted so
     34   // that it follows the normal pattern of stack-allocating ScopedFoo objects,
     35   // but the expiration handler needs to have a reference counted object to
     36   // refer to.
     37   class Core : public base::RefCountedThreadSafe<Core> {
     38    public:
     39     Core();
     40 
     41     // Informs the OS that the background task has completed.
     42     void EndBackgroundTask();
     43 
     44    private:
     45     friend base::RefCountedThreadSafe<Core>;
     46     ~Core();
     47 
     48     // |UIBackgroundTaskIdentifier| returned by
     49     // |beginBackgroundTaskWithExpirationHandler:| when marking the beginning of
     50     // a long-running background task. It is defined as an |unsigned int|
     51     // instead of a |UIBackgroundTaskIdentifier| so this class can be used in
     52     // .cc files.
     53     unsigned int background_task_id_;
     54     Lock background_task_id_lock_;
     55 
     56     DISALLOW_COPY_AND_ASSIGN(Core);
     57   };
     58 
     59   // The instance of the core that drives the background task.
     60   scoped_refptr<Core> core_;
     61 
     62   DISALLOW_COPY_AND_ASSIGN(ScopedCriticalAction);
     63 };
     64 
     65 }  // namespace ios
     66 }  // namespace base
     67 
     68 #endif  // BASE_IOS_SCOPED_CRITICAL_ACTION_H_
     69