michael@0: /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #include "nsISupports.idl"
michael@0: 
michael@0: /**
michael@0:  *
michael@0:  * nsIMemory: interface to allocate and deallocate memory. Also provides
michael@0:  * for notifications in low-memory situations.
michael@0:  *
michael@0:  * The frozen exported symbols NS_Alloc, NS_Realloc, and NS_Free
michael@0:  * provide a more efficient way to access XPCOM memory allocation. Using
michael@0:  * those symbols is preferred to using the methods on this interface.
michael@0:  *
michael@0:  * A client that wishes to be notified of low memory situations (for
michael@0:  * example, because the client maintains a large memory cache that
michael@0:  * could be released when memory is tight) should register with the
michael@0:  * observer service (see nsIObserverService) using the topic 
michael@0:  * "memory-pressure". There are three specific types of notications 
michael@0:  * that can occur.  These types will be passed as the |aData| 
michael@0:  * parameter of the of the "memory-pressure" notification: 
michael@0:  * 
michael@0:  * "low-memory"
michael@0:  * This will be passed as the extra data when the pressure 
michael@0:  * observer is being asked to flush for low-memory conditions.
michael@0:  *
michael@0:  * "low-memory-ongoing"
michael@0:  * This will be passed when we continue to be in a low-memory
michael@0:  * condition and we want to flush caches and do other cheap
michael@0:  * forms of memory minimization, but heavy handed approaches like
michael@0:  * a GC are unlikely to succeed.
michael@0:  *
michael@0:  * "-no-forward"
michael@0:  * This is appended to the above two parameters when the resulting
michael@0:  * notification should not be forwarded to the child processes.
michael@0:  *
michael@0:  * "heap-minimize"
michael@0:  * This will be passed as the extra data when the pressure 
michael@0:  * observer is being asked to flush because of a heap minimize 
michael@0:  * call.
michael@0:  *
michael@0:  * "alloc-failure"
michael@0:  * This will be passed as the extra data when the pressure 
michael@0:  * observer has been asked to flush because a malloc() or 
michael@0:  * realloc() has failed.
michael@0:  */
michael@0: 
michael@0: [scriptable, uuid(6aef11c4-8615-44a6-9711-98f43805693d)]
michael@0: interface nsIMemory : nsISupports
michael@0: {
michael@0:     /**
michael@0:      * Allocates a block of memory of a particular size. If the memory 
michael@0:      * cannot be allocated (because of an out-of-memory condition), the
michael@0:      * process aborts.
michael@0:      *
michael@0:      * @param size - the size of the block to allocate
michael@0:      * @result the block of memory
michael@0:      */
michael@0:     [noscript, notxpcom] voidPtr alloc(in size_t size);
michael@0: 
michael@0:     /**
michael@0:      * Reallocates a block of memory to a new size.
michael@0:      *
michael@0:      * @param ptr - the block of memory to reallocate
michael@0:      * @param size - the new size
michael@0:      * @result the reallocated block of memory
michael@0:      *
michael@0:      * If ptr is null, this function behaves like malloc.
michael@0:      * If s is the size of the block to which ptr points, the first
michael@0:      * min(s, size) bytes of ptr's block are copied to the new block.
michael@0:      * If the allocation succeeds, ptr is freed and a pointer to the 
michael@0:      * new block returned.  If the allocation fails, the process aborts.
michael@0:      */
michael@0:     [noscript, notxpcom] voidPtr realloc(in voidPtr ptr,
michael@0:                                          in size_t newSize);
michael@0: 
michael@0:     /**
michael@0:      * Frees a block of memory. Null is a permissible value, in which case
michael@0:      * nothing happens. 
michael@0:      *
michael@0:      * @param ptr - the block of memory to free
michael@0:      */
michael@0:     [noscript, notxpcom] void free(in voidPtr ptr);
michael@0: 
michael@0:     /**
michael@0:      * Attempts to shrink the heap.
michael@0:      * @param immediate - if true, heap minimization will occur
michael@0:      *   immediately if the call was made on the main thread. If
michael@0:      *   false, the flush will be scheduled to happen when the app is
michael@0:      *   idle.
michael@0:      * @throws NS_ERROR_FAILURE if 'immediate' is set an the call
michael@0:      *   was not on the application's main thread.
michael@0:      */
michael@0:     void heapMinimize(in boolean immediate);
michael@0: 
michael@0:     /**
michael@0:      * This predicate can be used to determine if we're in a low-memory
michael@0:      * situation (what constitutes low-memory is platform dependent). This
michael@0:      * can be used to trigger the memory pressure observers.
michael@0:      *
michael@0:      * DEPRECATED - Always returns false.  See bug 592308.
michael@0:      */
michael@0:     boolean isLowMemory();
michael@0: 
michael@0:     /**
michael@0:      * This predicate can be used to determine if the platform is a "low-memory"
michael@0:      * platform. Callers may use this to dynamically tune their behaviour
michael@0:      * to favour reduced memory usage at the expense of performance. The value
michael@0:      * returned by this function will not change over the lifetime of the process.
michael@0:      */
michael@0:     boolean isLowMemoryPlatform();
michael@0: };
michael@0: