java-tryLock可轮询可中断可定时的锁

1、从JAVA5.0开始,提供了新的选择:ReentrantLock。

2、可定时和可轮询的锁获取模式由tryLock方法实现。

3、使用tryLock试图获得的锁如果不能同时获得，就回退，并重新尝试。休眠时间由一个特定组件管理。（下面的代码完成转帐）

public boolean transferMoney(Account fromAcct,AccounttoAcct,DollarAmonunt amount,long timeout,TimeUnit unit)

   throwsInsufficientFundsException,InterruptedException{

   longfixedDelay=getFixedDelayComponentNanos(timeout,unit);

   longrandMod=getRandomDelayModulusNanos(timeout,unit);

   longstopTime=System.nanoTime()+unit.toNanos(timeout);

 

   while (true){

      if (fromAcct.lock.tryLock()){

          try{

                 if(toAcct.lock.tryLock()){

                    try {

                           if (fromAcct.getBalance().compareTo(amount)<0)

                               thrownew  InsufficientFundsException();

                           else {

                                fromAcct.debit(amount);

                               toAcct.credit(amount);

                                returntrue;

                           }

                     }finally{toAcct.lock.unlock();}    

                }

          }finally{fromAcct.lock.unlock();}

      }

   }

   if(System.nanoTime()<stopTime) return false;

  NANOSECONDS.sleep(fixedDelay+rnd.nextLong()%randMod);
}

4、具有时间限制的活动,定时锁同样有用.超时后程序提前返回.

public boolean trySendOnSharedLine(String message,longtimeout,TimeUnit unit)

               throwsInterruptedException{

       longnanosToLock=unit.toNanos(timeout)-estimatedNanosToSend(message);

       if (!lock.tryLock(nanosToLock,NANOSECONDS)) return false;

       try{

             return sendOnSharedLine(message);

        }finally{lock.unlock();}

}

5、一个可中断的锁可以响应中断，能取消。

public boolean sendOnSharedLine(Stringmessage) 

      throws InterruptedException{

    lock.lockInterruptibly();

    try{

        return cancellableSendOnSharedLine(message);

    }finally{

        lock.unlock();

    }

}

private boolean cancellableSendOnSharedLine(String message)

    throwsInterruptedException{...}

}