image/src/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_IMAGELIB_SHUTDOWNTRACKER_H_
  12 #define MOZILLA_IMAGELIB_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 many
  20  * 'xpcom-shutdown' notification observers on short-lived objects, which would
  21  * have an unnecessary performance cost.
  22  */
  23 struct ShutdownTracker
  24 {
  25   /**
  26    * Initialize static data. Called during imagelib module initialization.
  27    */
  28   static void Initialize();
  29
  30   /**
  31    * Check whether shutdown has started. Callers can use this to check whether
  32    * it's safe to access XPCOM services; if shutdown has started, such calls
  33    * must be avoided.
  34    *
  35    * @return true if shutdown has already started.
  36    */
  37   static bool ShutdownHasStarted();
  38
  39 private:
  40   virtual ~ShutdownTracker() = 0;  // Forbid instantiation.
  41 };
  42
  43 } // namespace image
  44 } // namespace mozilla
  45
  46 #endif // MOZILLA_IMAGELIB_SHUTDOWNTRACKER_H_