154 lines
5.2 KiB
Plaintext
154 lines
5.2 KiB
Plaintext
/*
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* Copyright 2007-2014 Haiku, Inc. All rights reserved.
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* Distributed under the terms of the MIT License.
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*
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* Authors:
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* Niels Sascha Reedijk, niels.reedijk@gmail.com
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* John Scipione, jscipione@gmail.com
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*
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* Proofreading:
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* David Weizades, ddewbofh@hotmail.com
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* Thom Holwerda, slakje@quicknet.nl
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*
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* Corresponds to:
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* headers/os/support/BlockCache.h rev 19972
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* src/kits/support/BlockCache.cpp rev 43545
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*/
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/*!
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\file BlockCache.h
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\ingroup support
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\ingroup libbe
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\brief Implements a mechanism to store and retrieve memory blocks.
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*/
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/*!
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\var B_OBJECT_CACHE
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\brief Used in the constructor of BBlockCache. Determines that objects will
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be created using \c new[] and \c delete[].
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\since BeOS R3
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*/
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/*!
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\var B_MALLOC_CACHE
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\brief Used in the constructor of BBlockCache. Determines that objects will
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be created using \c malloc() and \c free().
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\since BeOS R3
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*/
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/*!
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\class BBlockCache
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\ingroup support
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\ingroup libbe
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\brief A class that creates and maintains a pool of memory blocks.
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In some performance critical code there might come a time where you require
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a lot of little blocks of memory that you want to access and dispose of
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continuously. Since allocating and freeing memory are 'expensive'
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operations, it is better to have a pool of memory blocks at your disposal.
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Luckily, the Haiku API provides a class that will act as the administrator
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of your memory pool, so you will not have to reinvent the wheel every time.
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The principle is easy. The constructor takes the number of blocks you
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want to create beforehand, the size of the blocks, and the method of
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allocation. This can either be #B_OBJECT_CACHE or #B_MALLOC_CACHE.
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The first one uses C++ operators \c new[] and \c delete[], while the second
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one uses \c malloc() and \c free(). Unless you have specific demands on
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performance or you want to take care of freeing the objects yourself, either
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way works fine.
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As soon as you have the memory pool, you can Get() blocks. If the
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pre-allocated memory blocks run out, BBlockCache will allocate new ones, so
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you will not have to worry about availability. As soon as you are done you
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can Save() the memory back into the pool. BBlockCache will make sure that no
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more blocks will be saved than the initial number you requested when you
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created the object, so be aware of that.
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As soon as you got a pointer from the Get() method, you own that block of
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memory; this means that you have the liberty to dispose of it yourself. It
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also means that when you delete your BBlockCache instance, any blocks of
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memory that are checked out will not be destroyed. In case you might want to
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delete your objects yourself, make sure you free the memory the right way.
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If you created the object as #B_OBJECT_CACHE, use \c delete[] to free your
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object. If you created the object as #B_MALLOC_CACHE, use \c free(). Please
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note that it defeats the purpose of this class if your are going to free all
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the objects yourself since it basically means that when the pool runs out,
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Get() will be allocating the objects by itself.
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\note BBlockCache is thread-safe.
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\since BeOS R3
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*/
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/*!
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\fn BBlockCache::BBlockCache(uint32 blockCount, size_t blockSize, uint32
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allocationType)
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\brief Allocate a new memory pool.
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\param blockCount The number of free memory blocks you want to allocate
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initially. This number is also used as the maximum number of free
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blocks that will be kept.
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\param blockSize The size of the blocks.
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\param allocationType Either #B_OBJECT_CACHE for using \c new[] and
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\c delete[] or #B_MALLOC_CACHE for \c malloc() and \c free().
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\since BeOS R3
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*/
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/*!
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\fn BBlockCache::~BBlockCache()
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\brief Destroy the empty blocks in the free list.
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Note that the blocks you checked out with Get() and not checked back in with
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Save() will not be freed, since ownership belongs to you. Make sure you
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clean up after yourself.
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\since BeOS R3
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*/
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/*!
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\fn void* BBlockCache::Get(size_t blockSize)
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\brief Get a block from the pool of free blocks.
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If the pool runs out of free blocks, a new one will be allocated. Please
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note that if the size given in the \c blockSize parameter is different from
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the size given in the constructor, a new block of memory will be created.
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Only sizes that match the blocks in the memory pool will come from the pool.
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\param blockSize The required size of the memory block.
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\return Returns a pointer to a memory block, or \c NULL if locking the
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object failed.
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\since BeOS R3
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*/
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/*!
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\fn void BBlockCache::Save(void* pointer, size_t blockSize)
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\brief Save a block of memory to the memory pool.
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The block of memory will only be added to the pool if the \c blockSize is
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equal to the size the object was created with and if the maximum number of
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free blocks in the list will not be exceeded. If not, the memory will be
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freed.
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Note that it is perfectly valid to pass objects other than those you got
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from Get(), but please note that the way it was created conforms to the way
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memory is allocated and freed in this pool. Therefore, only feed blocks that
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were created with \c new[] if the allocation type is #B_OBJECT_CACHE.
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Likewise, you should only use objects allocated with \c malloc() when the
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allocation type is #B_MALLOC_CACHE.
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\since BeOS R3
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*/
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