xpcom/base/nsIMemory.idl

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   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 #include "nsISupports.idl"
   7
   8 /**
   9  *
  10  * nsIMemory: interface to allocate and deallocate memory. Also provides
  11  * for notifications in low-memory situations.
  12  *
  13  * The frozen exported symbols NS_Alloc, NS_Realloc, and NS_Free
  14  * provide a more efficient way to access XPCOM memory allocation. Using
  15  * those symbols is preferred to using the methods on this interface.
  16  *
  17  * A client that wishes to be notified of low memory situations (for
  18  * example, because the client maintains a large memory cache that
  19  * could be released when memory is tight) should register with the
  20  * observer service (see nsIObserverService) using the topic
  21  * "memory-pressure". There are three specific types of notications
  22  * that can occur.  These types will be passed as the |aData|
  23  * parameter of the of the "memory-pressure" notification:
  24  *
  25  * "low-memory"
  26  * This will be passed as the extra data when the pressure
  27  * observer is being asked to flush for low-memory conditions.
  28  *
  29  * "low-memory-ongoing"
  30  * This will be passed when we continue to be in a low-memory
  31  * condition and we want to flush caches and do other cheap
  32  * forms of memory minimization, but heavy handed approaches like
  33  * a GC are unlikely to succeed.
  34  *
  35  * "-no-forward"
  36  * This is appended to the above two parameters when the resulting
  37  * notification should not be forwarded to the child processes.
  38  *
  39  * "heap-minimize"
  40  * This will be passed as the extra data when the pressure
  41  * observer is being asked to flush because of a heap minimize
  42  * call.
  43  *
  44  * "alloc-failure"
  45  * This will be passed as the extra data when the pressure
  46  * observer has been asked to flush because a malloc() or
  47  * realloc() has failed.
  48  */
  49
  50 [scriptable, uuid(6aef11c4-8615-44a6-9711-98f43805693d)]
  51 interface nsIMemory : nsISupports
  52 {
  53     /**
  54      * Allocates a block of memory of a particular size. If the memory
  55      * cannot be allocated (because of an out-of-memory condition), the
  56      * process aborts.
  57      *
  58      * @param size - the size of the block to allocate
  59      * @result the block of memory
  60      */
  61     [noscript, notxpcom] voidPtr alloc(in size_t size);
  62
  63     /**
  64      * Reallocates a block of memory to a new size.
  65      *
  66      * @param ptr - the block of memory to reallocate
  67      * @param size - the new size
  68      * @result the reallocated block of memory
  69      *
  70      * If ptr is null, this function behaves like malloc.
  71      * If s is the size of the block to which ptr points, the first
  72      * min(s, size) bytes of ptr's block are copied to the new block.
  73      * If the allocation succeeds, ptr is freed and a pointer to the
  74      * new block returned.  If the allocation fails, the process aborts.
  75      */
  76     [noscript, notxpcom] voidPtr realloc(in voidPtr ptr,
  77                                          in size_t newSize);
  78
  79     /**
  80      * Frees a block of memory. Null is a permissible value, in which case
  81      * nothing happens.
  82      *
  83      * @param ptr - the block of memory to free
  84      */
  85     [noscript, notxpcom] void free(in voidPtr ptr);
  86
  87     /**
  88      * Attempts to shrink the heap.
  89      * @param immediate - if true, heap minimization will occur
  90      *   immediately if the call was made on the main thread. If
  91      *   false, the flush will be scheduled to happen when the app is
  92      *   idle.
  93      * @throws NS_ERROR_FAILURE if 'immediate' is set an the call
  94      *   was not on the application's main thread.
  95      */
  96     void heapMinimize(in boolean immediate);
  97
  98     /**
  99      * This predicate can be used to determine if we're in a low-memory
 100      * situation (what constitutes low-memory is platform dependent). This
 101      * can be used to trigger the memory pressure observers.
 102      *
 103      * DEPRECATED - Always returns false.  See bug 592308.
 104      */
 105     boolean isLowMemory();
 106
 107     /**
 108      * This predicate can be used to determine if the platform is a "low-memory"
 109      * platform. Callers may use this to dynamically tune their behaviour
 110      * to favour reduced memory usage at the expense of performance. The value
 111      * returned by this function will not change over the lifetime of the process.
 112      */
 113     boolean isLowMemoryPlatform();
 114 };
 115