/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * The contents of this file are subject to the Netscape Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation. All
 * Rights Reserved.
 *
 * Contributor(s): 
 */

/**
 * <font color="#FF0000"><b>    W A R N I N G
 * <p>This API is currently under review in preparation for making it an 
 * officially supported part of the mozilla platform. Please submit comments
 * to porkjockeys@mozilla.org before 6/15/00. Until that time, it is not 
 * advised to base commercial products on this API because it is subject to 
 * change. Use at your own risk!
 * </b></font>
 *
 * @status UNDER_REVIEW
 */

#include "nsISupports.idl"

interface nsIMemoryPressureObserver;

/**
 * nsIMemory: interface to allocate and deallocate memory. Also provides
 * for notifications in low-memory situations.
 */
[scriptable, uuid(59e7e77a-38e4-11d4-8cf5-0060b0fc14a3)]
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), null
     * is returned.
     *
     * @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, ptr is not freed
     * and null is returned. The returned value may be the same as ptr.
     */
    [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.
     */
    void heapMinimize();

    /**
     * Allows a memory pressure observer to be registered to provide a
     * callback for low-memory situations, allowing unnecessary objects to
     * be freed (e.g. flushing caches). Observers will be called either
     * before alloc or realloc are about to return null, or when
     * heapMinimize is called.
     * @param obs - the observer to register
     */
    void registerObserver(in nsIMemoryPressureObserver obs);

    /**
     * Allows a memory pressure observer to be unregistered.
     * @param obs - the observer to unregister
     */
    void unregisterObserver(in nsIMemoryPressureObserver obs);

    /**
     * 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 flushers.
     */
    boolean isLowMemory();
};

/**
 * nsIMemoryPressureObserver: interface for low-memory notification.
 */
[scriptable, uuid(fe6c8bd4-38e4-11d4-8cf5-0060b0fc14a3)]
interface nsIMemoryPressureObserver : nsISupports
{
    const unsigned long REASON_ALLOC_FAILURE = 0;
    const unsigned long REASON_HEAP_MINIMIZE = 1;

    /**
     * Called in response to a low-memory condition. 
     * @param reason - either REASON_ALLOC_FAILURE when alloc or realloc 
     *                 fails, or REASON_HEAP_MINIMIZE when heapMinimize is
     *                 called
     * @param requestedAmount - either the size requested by alloc or realloc,
     *                 or 0 if heapMinimize was called
     */
    void flushMemory(in unsigned long reason,
                     in size_t requestedAmount);
};