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source: vbox/trunk/src/libs/xpcom18a4/xpcom/ds/nsRecyclingAllocator.h@ 6542

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1/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2/* ***** BEGIN LICENSE BLOCK *****
3 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
4 *
5 * The contents of this file are subject to the Mozilla Public License Version
6 * 1.1 (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 * http://www.mozilla.org/MPL/
9 *
10 * Software distributed under the License is distributed on an "AS IS" basis,
11 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12 * for the specific language governing rights and limitations under the
13 * License.
14 *
15 * The Original Code is mozilla.org code.
16 *
17 * The Initial Developer of the Original Code is
18 * Netscape Communications Corporation.
19 * Portions created by the Initial Developer are Copyright (C) 2001, 2002
20 * the Initial Developer. All Rights Reserved.
21 *
22 * Contributor(s):
23 * Suresh Duddi <[email protected]>
24 *
25 * Alternatively, the contents of this file may be used under the terms of
26 * either the GNU General Public License Version 2 or later (the "GPL"), or
27 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
28 * in which case the provisions of the GPL or the LGPL are applicable instead
29 * of those above. If you wish to allow use of your version of this file only
30 * under the terms of either the GPL or the LGPL, and not to allow others to
31 * use your version of this file under the terms of the MPL, indicate your
32 * decision by deleting the provisions above and replace them with the notice
33 * and other provisions required by the GPL or the LGPL. If you do not delete
34 * the provisions above, a recipient may use your version of this file under
35 * the terms of any one of the MPL, the GPL or the LGPL.
36 *
37 * ***** END LICENSE BLOCK ***** */
38
39/*
40 * nsRecyclingAllocator
41 *
42 * This allocator is useful when we cycle through a small set of allocations
43 * repeatedly with minimal overlap. For eg. something we do for every gif
44 * file read (or) buffers required for decompression of every file from jar.
45 *
46 * What this does is keeps around the first set of memory allocated and
47 * reuses it subsequently. If all buckets are full, this falls back to
48 * malloc/free
49 *
50 * Uses a timer to release all memory allocated if not used for more than
51 * 10 secs automatically.
52 *
53 * Also there is a 4 byte maintenance overhead on every allocation.
54 *
55 * This allocator is thread safe.
56 *
57 * CAVEATS: As the number of buckets increases, this allocators performance
58 * will drop. As a general guideline, dont use this for more
59 * than NS_MAX_BLOCKS
60 */
61
62#ifndef nsRecyclingAllocator_h__
63#define nsRecyclingAllocator_h__
64
65#include "nscore.h"
66#include "pratom.h"
67#include "prlock.h"
68#include "nsIRecyclingAllocator.h"
69#include "nsIGenericFactory.h"
70
71#define NS_DEFAULT_RECYCLE_TIMEOUT 10 // secs
72#define NS_MAX_BLOCKS 24
73#define NS_ALLOCATOR_OVERHEAD_BYTES (sizeof(Block)) // bytes
74
75class nsITimer;
76class nsIMemory;
77
78class NS_COM nsRecyclingAllocator {
79 protected:
80 struct Block {
81 PRSize bytes;
82 };
83
84 // Make |BlockStoreNode| a |friend| so it can access |Block|.
85 struct BlockStoreNode;
86 friend struct BlockStoreNode;
87
88 struct BlockStoreNode {
89 BlockStoreNode() : bytes(0), block(nsnull), next(nsnull) {};
90 PRSize bytes;
91 Block *block;
92 BlockStoreNode *next;
93 };
94
95#define DATA(block) ((void *)(((char *)block) + NS_ALLOCATOR_OVERHEAD_BYTES))
96#define DATA_TO_BLOCK(data) ((Block *)((char *)(data) - NS_ALLOCATOR_OVERHEAD_BYTES))
97
98 // mMaxBlocks: Maximum number of blocks that can be allocated
99 PRUint32 mMaxBlocks;
100
101 // mBlocks:
102 // All blocks used or not.
103 BlockStoreNode *mBlocks;
104
105 // mFreeList
106 // A linked list of free blocks sorted by increasing order of size
107 BlockStoreNode* mFreeList;
108
109 // mNotUsedList
110 // A linked list of BlockStoreNodes that are not used to store
111 // any block information. When we add blocks into mFreeList, we
112 // take BlockStoreNode from here.
113 BlockStoreNode* mNotUsedList;
114
115 // mLock: Thread safety of mFreeList and mNotUsedList
116 PRLock *mLock;
117
118 // Timer for freeing unused memory
119 nsITimer *mRecycleTimer;
120
121 // mRecycleAfter:
122 // Allocator should be untouched for this many seconds for freeing
123 // unused Blocks.
124 PRUint32 mRecycleAfter;
125
126 // mTouched:
127 // says if the allocator touched any bucket. If allocator didn't touch
128 // any bucket over a time time interval, timer will call FreeUnusedBuckets()
129 PRInt32 mTouched;
130
131 // mId:
132 // a string for identifying the user of nsRecyclingAllocator
133 // User mainly for debug prints
134 const char *mId;
135
136#ifdef DEBUG
137 // mNAllocated: Number of blocks allocated
138 PRInt32 mNAllocated;
139#endif
140
141 public:
142
143 // nbucket : number of buckets to hold. Capped at NS_MAX_BUCKET
144 // recycleAfter : Try recycling allocated buckets after this many seconds
145 // id : a string used to identify debug prints. Will not be released.
146 nsRecyclingAllocator(PRUint32 nbucket = 0, PRUint32 recycleAfter = NS_DEFAULT_RECYCLE_TIMEOUT,
147 const char *id = NULL);
148 ~nsRecyclingAllocator();
149
150 nsresult Init(PRUint32 nbucket, PRUint32 recycleAfter, const char *id);
151
152 // Allocation and free routines
153 void* Malloc(PRSize size, PRBool zeroit = PR_FALSE);
154 void Free(void *ptr);
155
156 void* Calloc(PRUint32 items, PRSize size)
157 {
158 return Malloc(items * size, PR_TRUE);
159 }
160
161 // FreeUnusedBuckets - Frees any bucket memory that isn't in use
162 void FreeUnusedBuckets();
163
164 protected:
165
166 // Timer callback to trigger unused memory
167 static void nsRecycleTimerCallback(nsITimer *aTimer, void *aClosure);
168
169 // Freelist management
170 // FindFreeBlock: return a free block that can hold bytes (best fit)
171 Block* FindFreeBlock(PRSize bytes);
172 // AddToFreeList: adds block into our freelist for future retrieval.
173 // Returns PR_TRUE is addition was successful. PR_FALSE otherewise.
174 PRBool AddToFreeList(Block* block);
175
176 // Touch will mark that someone used this allocator
177 // Timer based release will free unused memory only if allocator
178 // was not touched for mRecycleAfter seconds.
179 void Touch() {
180 if (!mTouched)
181 PR_AtomicSet(&mTouched, 1);
182 }
183 void Untouch() {
184 PR_AtomicSet(&mTouched, 0);
185 }
186
187 friend void nsRecycleTimerCallback(nsITimer *aTimer, void *aClosure);
188};
189
190// ----------------------------------------------------------------------
191// Wrapping the recyling allocator with nsIMemory
192// ----------------------------------------------------------------------
193
194// Wrapping the nsRecyclingAllocator with nsIMemory
195class nsRecyclingAllocatorImpl : public nsRecyclingAllocator, public nsIRecyclingAllocator {
196public:
197 NS_DECL_ISUPPORTS
198 NS_DECL_NSIMEMORY
199 NS_DECL_NSIRECYCLINGALLOCATOR
200
201 nsRecyclingAllocatorImpl()
202 {
203 }
204
205private:
206 ~nsRecyclingAllocatorImpl() {}
207};
208#endif // nsRecyclingAllocator_h__
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