xpcom/base/nsMemory.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsMemory_h__
   8 #define nsMemory_h__
   9
  10 #include "nsError.h"
  11
  12 /**
  13  *
  14  * A client that wishes to be notified of low memory situations (for
  15  * example, because the client maintains a large memory cache that
  16  * could be released when memory is tight) should register with the
  17  * observer service (see nsIObserverService) using the topic
  18  * "memory-pressure".  There are specific types of notifications
  19  * that can occur.  These types will be passed as the |aData|
  20  * parameter of the of the "memory-pressure" notification:
  21  *
  22  * "low-memory"
  23  * This will be passed as the extra data when the pressure
  24  * observer is being asked to flush for low-memory conditions.
  25  *
  26  * "low-memory-ongoing"
  27  * This will be passed when we continue to be in a low-memory
  28  * condition and we want to flush caches and do other cheap
  29  * forms of memory minimization, but heavy handed approaches like
  30  * a GC are unlikely to succeed.
  31  *
  32  * "heap-minimize"
  33  * This will be passed as the extra data when the pressure
  34  * observer is being asked to flush because of a heap minimize
  35  * call.
  36  */
  37
  38 // This is implemented in nsMemoryImpl.cpp.
  39
  40 namespace nsMemory {
  41
  42 /**
  43  * Attempts to shrink the heap.
  44  * @param immediate - if true, heap minimization will occur
  45  *   immediately if the call was made on the main thread. If
  46  *   false, the flush will be scheduled to happen when the app is
  47  *   idle.
  48  * @throws NS_ERROR_FAILURE if 'immediate' is set and the call
  49  *   was not on the application's main thread.
  50  */
  51 nsresult HeapMinimize(bool aImmediate);
  52
  53 /**
  54  * This predicate can be used to determine if the platform is a "low-memory"
  55  * platform. Callers may use this to dynamically tune their behaviour
  56  * to favour reduced memory usage at the expense of performance. The value
  57  * returned by this function will not change over the lifetime of the process.
  58  */
  59 bool IsLowMemoryPlatform();
  60 }  // namespace nsMemory
  61
  62 #endif  // nsMemory_h__