зеркало из https://github.com/mozilla/pjs.git
202 строки
6.0 KiB
C++
202 строки
6.0 KiB
C++
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is mozilla.org code.
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*
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* The Initial Developer of the Original Code is
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* Netscape Communications Corporation.
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* Portions created by the Initial Developer are Copyright (C) 1998
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Chris Waterson <waterson@netscape.com
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either of the GNU General Public License Version 2 or later (the "GPL"),
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* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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/*
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A simple fixed-size allocator that allocates its memory from an
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arena.
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Although the allocator can handle blocks of any size, its
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preformance will degrade rapidly if used to allocate blocks of
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arbitrary size. Ideally, it should be used to allocate and recycle a
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large number of fixed-size blocks.
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Here is a typical usage pattern:
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#include NEW_H // You'll need this!
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#include "nsFixedSizeAllocator.h"
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// Say this is the object you want to allocate a ton of
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class Foo {
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public:
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// Implement placement new & delete operators that will
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// use the fixed size allocator.
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static Foo *
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Create(nsFixedSizeAllocator &aAllocator)
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{
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void *place = aAllocator.Alloc(sizeof(Foo));
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return place ? ::new (place) Foo() : nsnull;
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}
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static void
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Destroy(nsFixedSizeAllocator &aAllocator, Foo *aFoo)
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{
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aFoo->~Foo();
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aAllocator.Free(aFoo, sizeof(Foo));
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}
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// ctor & dtor
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Foo() {}
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~Foo() {}
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};
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int main(int argc, char* argv[])
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{
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// Somewhere in your code, you'll need to create an
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// nsFixedSizeAllocator object and initialize it:
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nsFixedSizeAllocator pool;
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// The fixed size allocator will support multiple fixed sizes.
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// This array lists an initial set of sizes that the allocator
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// should be prepared to support. In our case, there's just one,
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// which is Foo.
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static const size_t kBucketSizes[]
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= { sizeof(Foo) }
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// This is the number of different "buckets" you'll need for
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// fixed size objects. In our example, this will be "1".
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static const PRInt32 kNumBuckets
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= sizeof(kBucketSizes) / sizeof(size_t);
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// This is the intial size of the allocator, in bytes. We'll
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// assume that we want to start with space for 1024 Foo objects.
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static const PRInt32 kInitialPoolSize =
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NS_SIZE_IN_HEAP(sizeof(Foo)) * 1024;
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// Initialize (or re-initialize) the pool
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pool.Init("TheFooPool", kBucketSizes, kNumBuckets, kInitialPoolSize);
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// Now we can use the pool.
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// Create a new Foo object using the pool:
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Foo* foo = Foo::Create(pool);
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if (! foo) {
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// uh oh, out of memory!
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}
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// Delete the object. The memory used by `foo' is recycled in
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// the pool, and placed in a freelist
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Foo::Destroy(foo);
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// Create another foo: this one will be allocated from the
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// free-list
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foo = Foo::Create(pool);
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// When pool is destroyed, all of its memory is automatically
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// freed. N.B. it will *not* call your objects' destructors! In
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// this case, foo's ~Foo() method would never be called.
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}
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*/
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#ifndef nsFixedSizeAllocator_h__
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#define nsFixedSizeAllocator_h__
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#include "nscore.h"
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#include "nsError.h"
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#include "plarena.h"
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#define NS_SIZE_IN_HEAP(_size) (_size)
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class nsFixedSizeAllocator
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{
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protected:
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PLArenaPool mPool;
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struct Bucket;
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struct FreeEntry;
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friend struct Bucket;
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friend struct FreeEntry;
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struct FreeEntry {
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FreeEntry* mNext;
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};
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struct Bucket {
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size_t mSize;
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FreeEntry* mFirst;
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Bucket* mNext;
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};
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Bucket* mBuckets;
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Bucket *
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AddBucket(size_t aSize);
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Bucket *
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FindBucket(size_t aSize);
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public:
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nsFixedSizeAllocator() : mBuckets(nsnull) {}
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~nsFixedSizeAllocator() {
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if (mBuckets)
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PL_FinishArenaPool(&mPool);
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}
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/**
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* Initialize the fixed size allocator. 'aName' is used to tag
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* the underlying PLArena object for debugging and measurement
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* purposes. 'aNumBuckets' specifies the number of elements in
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* 'aBucketSizes', which is an array of integral block sizes
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* that this allocator should be prepared to handle.
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*/
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nsresult
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Init(const char* aName,
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const size_t* aBucketSizes,
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PRInt32 aNumBuckets,
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PRInt32 aInitialSize,
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PRInt32 aAlign = 0);
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/**
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* Allocate a block of memory 'aSize' bytes big.
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*/
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void* Alloc(size_t aSize);
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/**
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* Free a pointer allocated using a fixed-size allocator
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*/
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void Free(void* aPtr, size_t aSize);
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};
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#endif // nsFixedSizeAllocator_h__
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