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.

  • Field Details

  • Constructor Details

    • 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 Details

    • 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'.

    • newPoolMap

      Map<Integer, Queue<CachedBufferAllocator.CachedBuffer>> newPoolMap()

    • allocate

      public IoBuffer allocate(int requestedCapacity, boolean direct)
      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.
      Returns:
      The allocated IoBuffer

    • allocateNioBuffer

      public ByteBuffer allocateNioBuffer(int capacity, boolean direct)
      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.
      Returns:
      The allocated ByteBuffer

    • wrap

      public IoBuffer wrap(ByteBuffer nioBuffer)
      Wraps the specified NIO ByteBuffer into MINA buffer.
      Specified by:
      wrap in interface IoBufferAllocator
      Parameters:
      nioBuffer - The ByteBuffer to wrap
      Returns:
      The IoBuffer wrapping the ByteBuffer

    • dispose

      public void dispose()
      Dispose of this allocator.
      Specified by:
      dispose in interface IoBufferAllocator