JAVA并发编程有界缓存的实现详解

JAVA并发编程有界缓存的实现

1、有界缓存的基类

package cn.xf.cp.ch14;


public class baseBoundedBuffer
{
  private final V[] buf;
  private int tail;
  private int head;
  private int count;
  
  public baseBoundedBuffer(int capacity)
  {
    //初始化数组
    this.buf = (V[]) new Object[capacity];
  }
  
  //放入一个数据,final方法无法被重写
  protected synchronized final void doPut(V v)
  {
    buf[tail] = v;
    if(++tail == buf.length)
    {
      tail = 0;
    }
    //插入一个方法，总量++
    ++count;
  }
  
  
  protected synchronized final V doTake()
  {
    V v = buf[head];
    buf[head] = null;
    if(++head == buf.length)
    {
      head = 0;
    }
    --count;
    return v;
  }
  
  //通过对count的判断，来确定数组是否是满的
  public synchronized final boolean isFull()
  {
    return count == buf.length;
  }
  
  public synchronized final boolean isEmpty()
  {
    return count == 0;
  }
}

2、判定前提条件再执行操作

package cn.xf.cp.ch14;


public class GrumpyBoundedBuffer extends baseBoundedBuffer
{

  public GrumpyBoundedBuffer(int size)
  {
    super(size);
  }
  
  public synchronized void put(V v) throws Exception
  {
    //如果是满的队列，就无法插入新的元素
    if(this.isFull())
    {
      throw new Exception("队列超出");
    }
    this.doPut(v);
  }
  
  //同理，队列为空的就无法取出新的元素
  public synchronized V take() throws Exception
  {
    if(this.isEmpty())
    {
      throw new Exception("队列中无元素");
    }
    
    return this.doTake();
  }

}

3、通过轮询与休眠来实现简单的阻塞

package cn.xf.cp.ch14;


public class SleepyBoundedBuffer extends baseBoundedBuffer
{
  //2s
  private static final long SLEEP_GRANULARITY = 2000;

  public SleepyBoundedBuffer(int capacity)
  {
    super(capacity);
  }
  
  //放入队列的时候
  public void put(V v) throws InterruptedException
  {
    while(true)
    {
      //这里不对循环上锁，不然这个锁就无法释放了，不对休眠上锁，休眠上锁，在休眠的时候别人也无法操作，永远都不可能有元素出去
      synchronized (this)
      {
 //如果队列不是满的，那么就放入元素
 if(!this.isFull())
 {
   this.doPut(v);
   return;
 }
      }
      //否则休眠，退出cpu占用
      Thread.sleep(SLEEP_GRANULARITY);
    }
  }
  
  public V take() throws InterruptedException
  {
    while(true)
    {
      //这里不对循环上锁，不然这个锁就无法释放了，不对休眠上锁，休眠上锁，在休眠的时候别人也无法操作，永远都不可能有新的元素进来
      synchronized(this)
      {
 //如果数组部位空，那么就可以取出数据
 if(!this.isEmpty())
 {
   return this.doTake();
 }
 //如果队列为空，休眠几秒再试
      }
      Thread.sleep(SLEEP_GRANULARITY);
    }
  }
  
}

4、条件队列

package cn.xf.cp.ch14;


public class BoundedBuffer extends baseBoundedBuffer
{

  public BoundedBuffer(int capacity)
  {
    super(capacity);
  }
  
  
  public synchronized void put(V v) throws InterruptedException
  {
    while(this.isFull())
    {
      //这里挂起程序，会释放锁
      this.wait();
    }
    //如果队列不为满的，那么程序被唤醒之后从新获取锁
    this.doPut(v);
    //执行结束，唤醒其他队列
    this.notifyAll();
  }
  
  public synchronized V take() throws InterruptedException
  {
    while(this.isEmpty())
    {
      this.wait();
    }
    V v = this.doTake();
    this.notifyAll();
    return v;
  }
  
}

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