gecko-dev/xpcom/ds/nsRecyclingAllocator.h

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/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla 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/MPL/
*
* 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 the Initial Developer are Copyright (C) 2001, 2002
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Suresh Duddi <dp@netscape.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
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* decision by deleting the provisions above and replace them with the notice
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* the provisions above, a recipient may use your version of this file under
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*
* ***** END LICENSE BLOCK ***** */
/*
* nsRecyclingAllocator
*
* This allocator is useful when we cycle through a small set of allocations
* repeatedly with minimal overlap. For eg. something we do for every gif
* file read (or) buffers required for decompression of every file from jar.
*
* What this does is keeps around the first set of memory allocated and
* reuses it subsequently. If all buckets are full, this falls back to
* malloc/free
*
* Uses a timer to release all memory allocated if not used for more than
* 10 secs automatically.
*
* This allocator is thread safe.
*
* CAVEATS: As the number of buckets increases, this allocators performance
* will drop. As a general guideline, dont use this for more
* than NS_MAX_BUCKETS (10)
*/
#ifndef nsRecyclingAllocator_h__
#define nsRecyclingAllocator_h__
#include "nscore.h"
#include "pratom.h"
#define NS_DEFAULT_RECYCLE_TIMEOUT 10 // secs
#define NS_MAX_BUCKETS 10
class nsITimer;
class NS_COM nsRecyclingAllocator {
protected:
struct nsMemBucket {
void *ptr;
PRUint32 size;
// Is this bucket available ?
// 1 : free
// 0 or negative : in use
// This is an int because we use atomic inc/dec to operate on it
PRInt32 available;
};
PRUint32 mNBucket;
nsMemBucket *mMemBucket;
nsITimer *mRecycleTimer;
PRUint32 mRecycleAfter;
// mTouched : says if the allocator touched any bucket
// If allocator didn't touch any bucket over a time
// time interval, timer will call FreeUnusedBuckets()
PRInt32 mTouched;
// mNAllocations: says how many buckets still have memory.
// If all buckets were freed the last time
// around and allocator didn't touch any bucket, then
// there is nothing to be freed.
PRInt32 mNAllocations;
// mId: a string for identifying the user of nsRecyclingAllocator
// User mainly for debug prints
const char *mId;
public:
// nbucket : number of buckets to hold. Capped at NS_MAX_BUCKET
// recycleAfter : Try recycling allocated buckets after this many seconds
// id : a string used to identify debug prints. Will not be released.
nsRecyclingAllocator(PRUint32 nbucket, PRUint32 recycleAfter = NS_DEFAULT_RECYCLE_TIMEOUT,
const char *id = NULL);
~nsRecyclingAllocator();
// Allocation and free routines
void* Malloc(PRUint32 size, PRBool zeroit = PR_FALSE);
void Free(void *ptr);
void* Calloc(PRUint32 items, PRUint32 size)
{
return Malloc(items * size, PR_TRUE);
}
// FreeUnusedBuckets - Frees any bucket memory that isn't in use
void FreeUnusedBuckets();
protected:
// Timer callback to trigger unused memory
static void nsRecycleTimerCallback(nsITimer *aTimer, void *aClosure);
// Bucket handling
PRBool Claim(PRUint32 i)
{
PRBool claimed = (PR_AtomicDecrement(&mMemBucket[i].available) == 0);
// Undo the claim, if claim failed
if (!claimed)
Unclaim(i);
return claimed;
}
void Unclaim(PRUint32 i) { PR_AtomicIncrement(&mMemBucket[i].available); }
// Touch will mark that someone used this allocator
// Timer based release will free unused memory only if allocator
// was not touched for mRecycleAfter seconds.
void Touch() {
if (!mTouched)
PR_AtomicSet(&mTouched, 1);
}
void Untouch() {
PR_AtomicSet(&mTouched, 0);
}
friend void nsRecycleTimerCallback(nsITimer *aTimer, void *aClosure);
};
#endif // nsRecyclingAllocator_h__