Package com.google.code.yanf4j.buffer

Class CachedBufferAllocator

  • All Implemented Interfaces:
    IoBufferAllocator
    public class CachedBufferAllocator
extends java.lang.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 (Thu, 26 Jun 2008) $

    • Field Detail

      • DEFAULT_MAX_CACHED_BUFFER_SIZE

        private static final int DEFAULT_MAX_CACHED_BUFFER_SIZE
        See Also:
        Constant Field Values

      • maxPoolSize

        private final int maxPoolSize

      • maxCachedBufferSize

        private final int maxCachedBufferSize

    • 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 java.nio.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.