Patch by David Weizades

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@21208 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Niels Sascha Reedijk
2007-05-22 16:50:08 +00:00
parent 1a2a0e07c6
commit bdad0425c4
+37 -32
View File
@@ -2,8 +2,12 @@
* Copyright 2007, Haiku, Inc. All Rights Reserved.
* Distributed under the terms of the MIT License.
*
* Documentation by:
* Niels Sascha Reedijk <[email protected]>
* Authors:
* Niels Sascha Reedijk <[email protected]>
*
* Proofreading:
* David Weizades <[email protected]>
*
* Corresponds to:
* /trunk/headers/os/support/BlockCache.h rev 19972
* /trunk/src/kits/support/BlockCache.cpp rev 4568
@@ -34,37 +38,38 @@
In some performance critical code there might come a time where you
require a lot of little blocks of memory that you want to access and
dispose of continuously. Since allocating and freeing memory are an
'expensive' operation, it's better to have a pool of memory blocks at
dispose of continuously. Since allocating and freeing memory are
'expensive' operations, it's better to have a pool of memory blocks at
your disposal. Luckily, the Haiku API provides a class that will act
as the administrator of your memory pool, so you won't have to reinvent
the wheel.
as the administrator of your memory pool, so you will not have to reinvent
the wheel every time.
The principle is easy. The constructor takes the number of blocks you
want to create beforehand, the size of the blocks and the method of
allocation. This can either be #B_OBJECT_CACHE or #B_MALLOC_CACHE.
The first uses C++ operators \c new[] and \c delete[], the second uses
\c malloc() and \c free(). Unless you have specific demands on performance
or you want to take care of freeing the objects yourself, either use is fine.
The first one uses C++ operators \c new[] and \c delete[], the second one
uses \c malloc() and \c free(). Unless you have specific demands on
performance or you want to take care of freeing the objects yourself, either
way works fine.
As soon as you have the memory pool, you can Get() blocks. If the
pre-allocated memory blocks run out, BBlockCache will allocate
new ones, so you won't have to worry about availability. As soon as
you're done, you can Save() the memory back into the pool, though
BBlockCache will make sure that there won't be more blocks saved
than the initial number you said when you created the object.
new ones, so you will not have to worry about availability. As soon as
you are done you can Save() the memory back into the pool. BBlockCache will
make sure that there will not be more blocks saved than the initial number you
requested when you created the object, so be aware of that.
As soon as you got a pointer from the Get() method, you own that
block of memory. This means that you have the liberty to dispose
block of memory, this means that you have the liberty to dispose
of it yourself. It also means that when you delete your BBlockCache
instance, any blocks of memory that are checked out won't be destroyed.
instance, any blocks of memory that are checked out will not be destroyed.
In case you might want to delete your objects yourself, make sure you
use the proper way. If you created the object as #B_OBJECT_CACHE
use \c delete[] to free your object. If you created the object
as #B_MALLOC_CACHE, use \c free(). Please note that it defeats
the purpose of this class if your are going to free all the objects yourself,
since it basically means that when the pool runs out, Get() will be allocating
the objects itself.
free the memory the right way. If you created the object as #B_OBJECT_CACHE,
use \c delete[] to free your object. If you created the object as
#B_MALLOC_CACHE, use \c free(). Please note that it defeats the purpose of
this class if your are going to free all the objects yourself since it
basically means that when the pool runs out, Get() will be allocating the
objects by itself.
\note BBlockCache is thread-safe.
*/
@@ -73,9 +78,9 @@
\fn BBlockCache::BBlockCache(uint32 blockCount, size_t blockSize, uint32 allocationType)
\brief Allocate a new memory pool.
\param blockCount The number of free memory blocks you want to initially
allocate. This number is also used as a maximum number of free blocks that
will be kept.
\param blockCount The number of free memory blocks you want to allocate
initially. This number is also used as the maximum number of free blocks
that will be kept.
\param blockSize The size of the blocks.
\param allocationType Either #B_OBJECT_CACHE for using \c new[] and
\c delete[] or #B_MALLOC_CACHE for \c malloc() and \c free().
@@ -109,13 +114,13 @@
\brief Save a block of memory to the memory pool.
The block of memory will only be added to the pool if the \c blockSize is
equal to the size the object was created with, and if the maximum number
free blocks in the list won't be passed. Else the memory will be freeed.
equal to the size the object was created with and if the maximum number
free blocks in the list will not be exceeded. If not the memory will be freed.
Note that it is perfectly valid to pass objects other than you got from
Get(), but please note that the way it was created confirms with the way
memory is allocated and freed in this pool. Thus, only feed blocks that were
created with \c new[] if the allocation type is #B_OBJECT_CACHE, likewise
use only objects allocated with \c malloc() when the allocation type is
#B_MALLOC_CACHE.
Note that it is perfectly valid to pass objects other than those you got from
Get(), but please note that the way it was created conforms to the way memory
is allocated and freed in this pool. Therefor only feed blocks that were
created with \c new[] if the allocation type is #B_OBJECT_CACHE. Likewise
you should only use objects allocated with \c malloc() when the allocation
type is #B_MALLOC_CACHE.
*/