org.apache.mina.core.buffer
Class CachedBufferAllocator

java.lang.Object
  org.apache.mina.core.buffer.CachedBufferAllocator

All Implemented Interfaces:

IoBufferAllocator

public class CachedBufferAllocator
extends Object
implements IoBufferAllocator

An IoBufferAllocator that caches the buffers which are likely to be reused during auto-expansion of the buffers.

In SimpleBufferAllocator, the underlying ByteBuffer of the IoBuffer is reallocated on its capacity change, which means the newly allocated bigger ByteBuffer replaces the old small ByteBuffer. Consequently, the old ByteBuffer is marked for garbage collection.

It's not a problem in most cases as long as the capacity change doesn't happen frequently. However, once it happens too often, it burdens the VM and the cost of filling the newly allocated ByteBuffer with NUL surpass the cost of accessing the cache. In 2 dual-core Opteron Italy 270 processors, CachedBufferAllocator outperformed SimpleBufferAllocator in the following situation:

• when a 32 bytes buffer is expanded 4 or more times,
• when a 64 bytes buffer is expanded 4 or more times,
• when a 128 bytes buffer is expanded 2 or more times,
• and when a 256 bytes or bigger buffer is expanded 1 or more times.

Please note the observation above is subject to change in a different environment.

CachedBufferAllocator uses ThreadLocal to store the cached buffer, allocates buffers whose capacity is power of 2 only and provides performance advantage if IoBuffer.free() is called properly.

Version:

$Rev: 671827 $, $Date: 2008-06-26 10:49:48 +0200 (jeu, 26 jun 2008) $

Author:

The Apache MINA Project (dev@mina.apache.org)

Constructor Summary

CachedBufferAllocator()
Creates a new instance with the default parameters (#DEFAULT_MAX_POOL_SIZE and #DEFAULT_MAX_CACHED_BUFFER_SIZE).

CachedBufferAllocator(int maxPoolSize, int maxCachedBufferSize)
Creates a new instance.

Method Summary

IoBuffer	allocate(int requestedCapacity, boolean direct) Returns the buffer which is capable of the specified size.
ByteBuffer	allocateNioBuffer(int capacity, boolean direct) Returns the NIO buffer which is capable of the specified size.
void	dispose() Dispose of this allocator.
int	getMaxCachedBufferSize() Returns the maximum capacity of a cached buffer.
int	getMaxPoolSize() Returns the maximum number of buffers with the same capacity per thread.
IoBuffer	wrap(ByteBuffer nioBuffer) Wraps the specified NIO ByteBuffer into MINA buffer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CachedBufferAllocator

public CachedBufferAllocator()

Creates a new instance with the default parameters (#DEFAULT_MAX_POOL_SIZE and #DEFAULT_MAX_CACHED_BUFFER_SIZE).

CachedBufferAllocator

public CachedBufferAllocator(int maxPoolSize,
                             int maxCachedBufferSize)

Creates a new instance.

Parameters:

maxPoolSize - the maximum number of buffers with the same capacity per thread. 0 disables this limitation.

maxCachedBufferSize - the maximum capacity of a cached buffer. A buffer whose capacity is bigger than this value is not pooled. 0 disables this limitation.

Method Detail

getMaxPoolSize

public int getMaxPoolSize()

Returns the maximum number of buffers with the same capacity per thread. 0 means 'no limitation'.

getMaxCachedBufferSize

public int getMaxCachedBufferSize()

Returns the maximum capacity of a cached buffer. A buffer whose capacity is bigger than this value is not pooled. 0 means 'no limitation'.

allocate

public IoBuffer allocate(int requestedCapacity,
                         boolean direct)

Description copied from interface: IoBufferAllocator

Returns the buffer which is capable of the specified size.

Specified by:

allocate in interface IoBufferAllocator

Parameters:

requestedCapacity - the capacity of the buffer

direct - true to get a direct buffer, false to get a heap buffer.

allocateNioBuffer

public ByteBuffer allocateNioBuffer(int capacity,
                                    boolean direct)

Description copied from interface: IoBufferAllocator

Returns the NIO buffer which is capable of the specified size.

Specified by:

allocateNioBuffer in interface IoBufferAllocator

Parameters:

capacity - the capacity of the buffer

direct - true to get a direct buffer, false to get a heap buffer.

wrap

public IoBuffer wrap(ByteBuffer nioBuffer)

Description copied from interface: IoBufferAllocator

Wraps the specified NIO ByteBuffer into MINA buffer.

Specified by:

wrap in interface IoBufferAllocator

dispose

public void dispose()

Description copied from interface: IoBufferAllocator

Dispose of this allocator.

Specified by:

dispose in interface IoBufferAllocator