xpcom/base/nsIMemory.idl

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  37
  38 #include "nsISupports.idl"
  39
  40 /**
  41  *
  42  * nsIMemory: interface to allocate and deallocate memory. Also provides
  43  * for notifications in low-memory situations.
  44  *
  45  * The frozen exported symbols NS_Alloc, NS_Realloc, and NS_Free
  46  * provide a more efficient way to access XPCOM memory allocation. Using
  47  * those symbols is preferred to using the methods on this interface.
  48  *
  49  * A client that wishes to be notified of low memory situations (for
  50  * example, because the client maintains a large memory cache that
  51  * could be released when memory is tight) should register with the
  52  * observer service (see nsIObserverService) using the topic
  53  * "memory-pressure". There are three specific types of notications
  54  * that can occur.  These types will be passed as the |aData|
  55  * parameter of the of the "memory-pressure" notification:
  56  *
  57  * "low-memory"
  58  * This will be passed as the extra data when the pressure
  59  * observer is being asked to flush for low-memory conditions.
  60  *
  61  * "heap-minimize"
  62  * This will be passed as the extra data when the pressure
  63  * observer is being asked to flush because of a heap minimize
  64  * call.
  65  *
  66  * "alloc-failure"
  67  * This will be passed as the extra data when the pressure
  68  * observer has been asked to flush because a malloc() or
  69  * realloc() has failed.
  70  *
  71  * @status FROZEN
  72  */
  73
  74 [scriptable, uuid(59e7e77a-38e4-11d4-8cf5-0060b0fc14a3)]
  75 interface nsIMemory : nsISupports
  76 {
  77     /**
  78      * Allocates a block of memory of a particular size. If the memory
  79      * cannot be allocated (because of an out-of-memory condition), null
  80      * is returned.
  81      *
  82      * @param size - the size of the block to allocate
  83      * @result the block of memory
  84      */
  85     [noscript, notxpcom] voidPtr alloc(in size_t size);
  86
  87     /**
  88      * Reallocates a block of memory to a new size.
  89      *
  90      * @param ptr - the block of memory to reallocate
  91      * @param size - the new size
  92      * @result the reallocated block of memory
  93      *
  94      * If ptr is null, this function behaves like malloc.
  95      * If s is the size of the block to which ptr points, the first
  96      * min(s, size) bytes of ptr's block are copied to the new block.
  97      * If the allocation succeeds, ptr is freed and a pointer to the
  98      * new block returned.  If the allocation fails, ptr is not freed
  99      * and null is returned. The returned value may be the same as ptr.
 100      */
 101     [noscript, notxpcom] voidPtr realloc(in voidPtr ptr,
 102                                          in size_t newSize);
 103
 104     /**
 105      * Frees a block of memory. Null is a permissible value, in which case
 106      * nothing happens.
 107      *
 108      * @param ptr - the block of memory to free
 109      */
 110     [noscript, notxpcom] void free(in voidPtr ptr);
 111
 112     /**
 113      * Attempts to shrink the heap.
 114      * @param immediate - if true, heap minimization will occur
 115      *   immediately if the call was made on the main thread. If
 116      *   false, the flush will be scheduled to happen when the app is
 117      *   idle.
 118      * @return NS_ERROR_FAILURE if 'immediate' is set an the call
 119      *   was not on the application's main thread.
 120      */
 121     void heapMinimize(in boolean immediate);
 122
 123     /**
 124      * This predicate can be used to determine if we're in a low-memory
 125      * situation (what constitutes low-memory is platform dependent). This
 126      * can be used to trigger the memory pressure observers.
 127      */
 128     boolean isLowMemory();
 129 };
 130