base/ios/scoped_critical_action.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 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_