gecko-dev/xpcom/base/nsIMemory.idl

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "nsISupports.idl"
/**
*
* nsIMemory: interface to allocate and deallocate memory. Also provides
* for notifications in low-memory situations.
*
* The frozen exported symbols NS_Alloc, NS_Realloc, and NS_Free
* provide a more efficient way to access XPCOM memory allocation. Using
* those symbols is preferred to using the methods on this interface.
*
* A client that wishes to be notified of low memory situations (for
* example, because the client maintains a large memory cache that
* could be released when memory is tight) should register with the
* observer service (see nsIObserverService) using the topic
* "memory-pressure". There are three specific types of notications
* that can occur. These types will be passed as the |aData|
* parameter of the of the "memory-pressure" notification:
*
* "low-memory"
* This will be passed as the extra data when the pressure
* observer is being asked to flush for low-memory conditions.
*
* "low-memory-ongoing"
* This will be passed when we continue to be in a low-memory
* condition and we want to flush caches and do other cheap
* forms of memory minimization, but heavy handed approaches like
* a GC are unlikely to succeed.
*
* "-no-forward"
* This is appended to the above two parameters when the resulting
* notification should not be forwarded to the child processes.
*
* "heap-minimize"
* This will be passed as the extra data when the pressure
* observer is being asked to flush because of a heap minimize
* call.
*
* "alloc-failure"
* This will be passed as the extra data when the pressure
* observer has been asked to flush because a malloc() or
* realloc() has failed.
*/
[scriptable, uuid(6aef11c4-8615-44a6-9711-98f43805693d)]
interface nsIMemory : nsISupports
{
/**
* Allocates a block of memory of a particular size. If the memory
* cannot be allocated (because of an out-of-memory condition), the
* process aborts.
*
* @param size - the size of the block to allocate
* @result the block of memory
*/
[noscript, notxpcom] voidPtr alloc(in size_t size);
/**
* Reallocates a block of memory to a new size.
*
* @param ptr - the block of memory to reallocate
* @param size - the new size
* @result the reallocated block of memory
*
* If ptr is null, this function behaves like malloc.
* If s is the size of the block to which ptr points, the first
* min(s, size) bytes of ptr's block are copied to the new block.
* If the allocation succeeds, ptr is freed and a pointer to the
* new block returned. If the allocation fails, the process aborts.
*/
[noscript, notxpcom] voidPtr realloc(in voidPtr ptr,
in size_t newSize);
/**
* Frees a block of memory. Null is a permissible value, in which case
* nothing happens.
*
* @param ptr - the block of memory to free
*/
[noscript, notxpcom] void free(in voidPtr ptr);
/**
* Attempts to shrink the heap.
* @param immediate - if true, heap minimization will occur
* immediately if the call was made on the main thread. If
* false, the flush will be scheduled to happen when the app is
* idle.
* @throws NS_ERROR_FAILURE if 'immediate' is set an the call
* was not on the application's main thread.
*/
void heapMinimize(in boolean immediate);
/**
* This predicate can be used to determine if we're in a low-memory
* situation (what constitutes low-memory is platform dependent). This
* can be used to trigger the memory pressure observers.
*
* DEPRECATED - Always returns false. See bug 592308.
*/
boolean isLowMemory();
/**
* This predicate can be used to determine if the platform is a "low-memory"
* platform. Callers may use this to dynamically tune their behaviour
* to favour reduced memory usage at the expense of performance. The value
* returned by this function will not change over the lifetime of the process.
*/
boolean isLowMemoryPlatform();
};