xpcom/ds/nsFixedSizeAllocator.cpp

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  15  * The Original Code is mozilla.org code.
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  17  * The Initial Developer of the Original Code is
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  19  * Portions created by the Initial Developer are Copyright (C) 1998
  20  * the Initial Developer. All Rights Reserved.
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  22  * Contributor(s):
  23  *   Chris Waterson <waterson@netscape.com
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  25  * Alternatively, the contents of this file may be used under the terms of
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  37  * ***** END LICENSE BLOCK ***** */
  38
  39 /*
  40
  41   Implementation for nsFixedSizeAllocator
  42
  43 */
  44
  45 #include "nsCRT.h"
  46 #include "nsFixedSizeAllocator.h"
  47
  48 nsFixedSizeAllocator::Bucket *
  49 nsFixedSizeAllocator::AddBucket(size_t aSize)
  50 {
  51     void* p;
  52     PL_ARENA_ALLOCATE(p, &mPool, sizeof(Bucket));
  53     if (! p)
  54         return nsnull;
  55
  56     Bucket* bucket = static_cast<Bucket*>(p);
  57     bucket->mSize  = aSize;
  58     bucket->mFirst = nsnull;
  59     bucket->mNext  = mBuckets;
  60
  61     mBuckets = bucket;
  62     return bucket;
  63 }
  64
  65 nsresult
  66 nsFixedSizeAllocator::Init(const char* aName,
  67                            const size_t* aBucketSizes,
  68                            PRInt32 aNumBuckets,
  69                            PRInt32 aInitialSize,
  70                            PRInt32 aAlign)
  71 {
  72     NS_PRECONDITION(aNumBuckets > 0, "no buckets");
  73     if (aNumBuckets <= 0)
  74         return NS_ERROR_INVALID_ARG;
  75
  76     // Blow away the old pool if we're being re-initialized.
  77     if (mBuckets)
  78         PL_FinishArenaPool(&mPool);
  79
  80     PRInt32 bucketspace = aNumBuckets * sizeof(Bucket);
  81     PL_InitArenaPool(&mPool, aName, bucketspace + aInitialSize, aAlign);
  82
  83     mBuckets = nsnull;
  84     for (PRInt32 i = 0; i < aNumBuckets; ++i)
  85         AddBucket(aBucketSizes[i]);
  86
  87     return NS_OK;
  88 }
  89
  90 nsFixedSizeAllocator::Bucket *
  91 nsFixedSizeAllocator::FindBucket(size_t aSize)
  92 {
  93     Bucket** link = &mBuckets;
  94     Bucket* bucket;
  95
  96     while ((bucket = *link) != nsnull) {
  97         if (aSize == bucket->mSize) {
  98             // Promote to the head of the list, under the assumption
  99             // that we'll allocate same-sized object contemporaneously.
 100             *link = bucket->mNext;
 101             bucket->mNext = mBuckets;
 102             mBuckets = bucket;
 103             return bucket;
 104         }
 105
 106         link = &bucket->mNext;
 107     }
 108     return nsnull;
 109 }
 110
 111 void*
 112 nsFixedSizeAllocator::Alloc(size_t aSize)
 113 {
 114     Bucket* bucket = FindBucket(aSize);
 115     if (! bucket) {
 116         // Oops, we don't carry that size. Let's fix that.
 117         bucket = AddBucket(aSize);
 118         if (! bucket)
 119             return nsnull;
 120     }
 121
 122     void* next;
 123     if (bucket->mFirst) {
 124         next = bucket->mFirst;
 125         bucket->mFirst = bucket->mFirst->mNext;
 126     }
 127     else {
 128         PL_ARENA_ALLOCATE(next, &mPool, aSize);
 129         if (!next)
 130             return nsnull;
 131     }
 132
 133 #ifdef DEBUG
 134     memset(next, 0xc8, aSize);
 135 #endif
 136
 137     return next;
 138 }
 139
 140 void
 141 nsFixedSizeAllocator::Free(void* aPtr, size_t aSize)
 142 {
 143     FreeEntry* entry = reinterpret_cast<FreeEntry*>(aPtr);
 144     Bucket* bucket = FindBucket(aSize);
 145
 146 #ifdef DEBUG
 147     NS_ASSERTION(bucket && bucket->mSize == aSize, "ack! corruption! bucket->mSize != aSize!");
 148     memset(aPtr, 0xd8, bucket->mSize);
 149 #endif
 150
 151     entry->mNext = bucket->mFirst;
 152     bucket->mFirst = entry;
 153 }