Akka/Scala example source code file (DirectByteBufferPool.scala)

This example Akka source code file (DirectByteBufferPool.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Akka and Scala source code examples by using tags.

All credit for the original source code belongs to akka.io; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Akka tags/keywords

akka, array, atomicboolean, bufferpool, bytebuffer, directbytebufferpool, int, io, unit

The DirectByteBufferPool.scala Akka example source code

/**
 * Copyright (C) 2009-2014 Typesafe Inc. <http://www.typesafe.com>
 */

package akka.io

import java.util.concurrent.atomic.AtomicBoolean
import java.nio.ByteBuffer
import annotation.tailrec

trait BufferPool {
  def acquire(): ByteBuffer
  def release(buf: ByteBuffer)
}

/**
 * INTERNAL API
 *
 * A buffer pool which keeps a free list of direct buffers of a specified default
 * size in a simple fixed size stack.
 *
 * If the stack is full a buffer offered back is not kept but will be let for
 * being freed by normal garbage collection.
 */
private[akka] class DirectByteBufferPool(defaultBufferSize: Int, maxPoolEntries: Int) extends BufferPool {
  private[this] val locked = new AtomicBoolean(false)
  private[this] val pool: Array[ByteBuffer] = new Array[ByteBuffer](maxPoolEntries)
  private[this] var buffersInPool: Int = 0

  def acquire(): ByteBuffer =
    takeBufferFromPool()

  def release(buf: ByteBuffer): Unit =
    offerBufferToPool(buf)

  private def allocate(size: Int): ByteBuffer =
    ByteBuffer.allocateDirect(size)

  @tailrec
  private final def takeBufferFromPool(): ByteBuffer =
    if (locked.compareAndSet(false, true)) {
      val buffer =
        try if (buffersInPool > 0) {
          buffersInPool -= 1
          pool(buffersInPool)
        } else null
        finally locked.set(false)

      // allocate new and clear outside the lock
      if (buffer == null)
        allocate(defaultBufferSize)
      else {
        buffer.clear()
        buffer
      }
    } else takeBufferFromPool() // spin while locked

  @tailrec
  private final def offerBufferToPool(buf: ByteBuffer): Unit =
    if (locked.compareAndSet(false, true))
      try if (buffersInPool < maxPoolEntries) {
        pool(buffersInPool) = buf
        buffersInPool += 1
      } // else let the buffer be gc'd
      finally locked.set(false)
    else offerBufferToPool(buf) // spin while locked
}