gecko-dev/xpcom/ds/nsFixedSizeAllocator.cpp

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C++

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
Implementation for nsFixedSizeAllocator
*/
#include "nsCRT.h"
#include "nsFixedSizeAllocator.h"
nsFixedSizeAllocator::Bucket *
nsFixedSizeAllocator::AddBucket(size_t aSize)
{
void* p;
PL_ARENA_ALLOCATE(p, &mPool, sizeof(Bucket));
if (! p)
return nullptr;
Bucket* bucket = static_cast<Bucket*>(p);
bucket->mSize = aSize;
bucket->mFirst = nullptr;
bucket->mNext = mBuckets;
mBuckets = bucket;
return bucket;
}
nsresult
nsFixedSizeAllocator::Init(const char* aName,
const size_t* aBucketSizes,
int32_t aNumBuckets,
int32_t aInitialSize,
int32_t aAlign)
{
NS_PRECONDITION(aNumBuckets > 0, "no buckets");
if (aNumBuckets <= 0)
return NS_ERROR_INVALID_ARG;
// Blow away the old pool if we're being re-initialized.
if (mBuckets)
PL_FinishArenaPool(&mPool);
int32_t bucketspace = aNumBuckets * sizeof(Bucket);
PL_InitArenaPool(&mPool, aName, bucketspace + aInitialSize, aAlign);
mBuckets = nullptr;
for (int32_t i = 0; i < aNumBuckets; ++i)
AddBucket(aBucketSizes[i]);
return NS_OK;
}
nsFixedSizeAllocator::Bucket *
nsFixedSizeAllocator::FindBucket(size_t aSize)
{
Bucket** link = &mBuckets;
Bucket* bucket;
while ((bucket = *link) != nullptr) {
if (aSize == bucket->mSize) {
// Promote to the head of the list, under the assumption
// that we'll allocate same-sized object contemporaneously.
*link = bucket->mNext;
bucket->mNext = mBuckets;
mBuckets = bucket;
return bucket;
}
link = &bucket->mNext;
}
return nullptr;
}
void*
nsFixedSizeAllocator::Alloc(size_t aSize)
{
Bucket* bucket = FindBucket(aSize);
if (! bucket) {
// Oops, we don't carry that size. Let's fix that.
bucket = AddBucket(aSize);
if (! bucket)
return nullptr;
}
void* next;
if (bucket->mFirst) {
next = bucket->mFirst;
bucket->mFirst = bucket->mFirst->mNext;
}
else {
PL_ARENA_ALLOCATE(next, &mPool, aSize);
if (!next)
return nullptr;
}
#ifdef DEBUG
memset(next, 0xc8, aSize);
#endif
return next;
}
void
nsFixedSizeAllocator::Free(void* aPtr, size_t aSize)
{
FreeEntry* entry = reinterpret_cast<FreeEntry*>(aPtr);
Bucket* bucket = FindBucket(aSize);
#ifdef DEBUG
NS_ASSERTION(bucket && bucket->mSize == aSize, "ack! corruption! bucket->mSize != aSize!");
memset(aPtr, 0xd8, bucket->mSize);
#endif
entry->mNext = bucket->mFirst;
bucket->mFirst = entry;
}