image/ShutdownTracker.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 /**
   7  * ShutdownTracker is an imagelib-global service that allows callers to check
   8  * whether shutdown has started.
   9  */
  10
  11 #ifndef mozilla_image_ShutdownTracker_h
  12 #define mozilla_image_ShutdownTracker_h
  13
  14 namespace mozilla {
  15 namespace image {
  16
  17 /**
  18  * ShutdownTracker is an imagelib-global service that allows callers to check
  19  * whether shutdown has started. It exists to avoid the need for registering
  20  * many 'xpcom-will-shutdown' notification observers on short-lived objects,
  21  * which would have an unnecessary performance cost.
  22  */
  23 struct ShutdownTracker {
  24   /**
  25    * Initialize static data. Called during imagelib module initialization.
  26    */
  27   static void Initialize();
  28
  29   /**
  30    * Check whether shutdown has started. Callers can use this to check whether
  31    * it's safe to access XPCOM services; if shutdown has started, such calls
  32    * must be avoided.
  33    *
  34    * @return true if shutdown has already started.
  35    */
  36   static bool ShutdownHasStarted();
  37
  38  private:
  39   virtual ~ShutdownTracker() = 0;  // Forbid instantiation.
  40 };
  41
  42 }  // namespace image
  43 }  // namespace mozilla
  44
  45 #endif  // mozilla_image_ShutdownTracker_h