我已经使用线程(等待和通知)功能创建了一个生产者使用者程序。该代码是-

/**
 *  Message.java ( Common object )
 */
package threads;

import java.util.concurrent.locks.ReentrantLock;

/**
 * @author chouhan_r
 *
 */
public class Message {
    private String message;

    ReentrantLock lock = new ReentrantLock();
    ReentrantLock takelock = new ReentrantLock();
    private boolean empty =true;
    public  void put(String message){
        lock.lock();
        while(!empty){
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        empty = false;
        this.message = message;

        notifyAll();
        lock.unlock();
    }

    public String take(){

        takelock.lock();
        while(empty){
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        empty = true;

        notifyAll();
        takelock.unlock();
        return message;

    }


}


/**
 * Producer.java
 */
package threads;

import java.util.Random;

public class Producer implements Runnable{
    private Message message;
    public Producer(Message message) {
        this.message = message;
    }

    @Override
    public void run() {
        String[] impInfo = {"Hello", "I am here", "why are you doing this ??", "No problem" };
        Random random = new Random();
        for(String str : impInfo){
            message.put(str);
            try {
                Thread.sleep(random.nextInt(3000));
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        message.put("Finished");

    }



}

/**
 * Consumer.java
 */
package threads;

public class Consumer implements Runnable{
    private Message message;
    public Consumer(Message message) {
        this.message = message;
    }
    @Override
    public void run() {
        System.out.println(message);
        String msg = message.take();
        while(!"Finished".equalsIgnoreCase(msg)){
            System.out.println(msg);
            msg = message.take();
        }


    }


}


=====================

/**
 * Main Program
 */
package threads;

public class ProConsTest {

    public static void main(String[] args) {
        Message message = new Message();
        new Thread(new Consumer(message)).start();
        new Thread(new Producer(message)).start();



    }

}


我正在尝试使用ReentrantLock执行此代码,但它给了我followin错误-

Exception in thread "Thread-0" java.lang.IllegalMonitorStateException
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Unknown Source)
    at threads.Message.take(Message.java:39)
    at threads.Consumer.run(Consumer.java:11)
    at java.lang.Thread.run(Unknown Source)
Exception in thread "Thread-1" java.lang.IllegalMonitorStateException
    at java.lang.Object.notifyAll(Native Method)
    at threads.Message.put(Message.java:31)
    at threads.Producer.run(Producer.java:16)
    at java.lang.Thread.run(Unknown Source)


我在这里做错什么了吗?当我在Message.java中将方法标记为同步时,它可以正常工作。我们只能使用可重入锁运行此代码吗?

最佳答案

Object.waitObject.notify连接到内部锁定功能,该功能与synchronized块和方法一起使用。

如果要使用Lock,则不能使用这两种方法。取而代之的是,您必须create a Condition并在其上调用await(),它应与同一signal()实例上另一个调用Condition的线程配对。请注意,与Object.waitObject.notify不同,每个Condition可以有多个Lock,并且在同一signal实例上调用Condition的线程将唤醒等待特定条件的线程。

但是,与内部锁定功能一样,在Condition上调用方法之前,必须拥有关联的锁定。如果是ReadWriteLock,则必须拥有写锁。

不幸的是,Conditionwait继承了方法notifyObject,因此切勿将它们混在一起很重要,由于难以区分名称waitawait,因此需要特别注意。

documentation of Condition包含一个完整的示例。我只是拿起一个代码片段来说明put方法中的用法:


final Lock lock = new ReentrantLock();
final Condition notFull  = lock.newCondition();
final Condition notEmpty = lock.newCondition();

  
  …

lock.lock();
try {
  while (count == items.length)
    notFull.await();
  items[putptr] = x;
  if (++putptr == items.length) putptr = 0;
  ++count;
  notEmpty.signal();
} finally {
  lock.unlock();
}

10-06 10:32
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