1

I was going through threads and I read that the notify() method is used to send a signal to one and only one of the threads that are waiting in that same object's waiting pool. The method notifyAll() works in the same way as notify(), only it sends the signal to all of the threads waiting on the Object.

Now my query is that if let's say I have 5 threads and one main thread, so initially the main thread starts and then five other threads start. Now I want to send notification to third thread only. How could it be possible with the use of notify(), since here I am sending notification to third thread only? Please advise.

4

2 回答 2

3

如果你想通知一个特定的线程，让它wait()在一个不同的对象上，然后调用notify()这个对象。

于 2012-04-15T04:11:19.957 回答
3

ReentrantLocksynchronized类通过允许每个对象有多个等待集，为您提供比关键字更细粒度的控制。

您可以使用ReentrantLock从ReentrantLock获取多个条件。然后一个线程可能会调用（在功能上与 类似）并将阻塞直到另一个线程调用（在功能上与 类似）。ReentrantLock.newCondition()Condition.await()Object.wait()Condition.signal()Object.notify()

不同之处在于您可以Conditions为单个ReentrantLock. 因此，您可以Condition为每个创建一个Thread并调用与您想要唤醒signal()的条件相对应的条件。Thread

这是一个演示上述内容的简单示例代码。它创建了 5 个Threads，它们都等待不同Conditions的相同ReentrantLock。然后主线程调用signal()以唤醒特定的Threads.

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class ReentranLockTest
{
    public static void main( String[] args )
    {
        final ReentrantLock lock = new ReentrantLock( );

        int numThreads = 5;

        Condition[] conditions = new Condition[numThreads];

        // start five threads, storing their associated Conditions
        for ( int i = 0; i < numThreads; i++ )
        {
            final int threadNumber = i;

            System.out.printf( "Started thread number %d%n", threadNumber );

            // to create a Condition we must lock the associated ReentrantLock
            lock.lock( );
            try
            {
                final Condition condition = lock.newCondition( );
                conditions[i] = condition;

                // start the worker Thread
                ( new Thread( )
                {
                    @Override
                    public void run( )
                    {
                        // wait on the Condition
                        // to do so we must be holding the
                        // associated ReentrantLock
                        lock.lock( );
                        try
                        {
                            condition.await( );
                        }
                        catch ( InterruptedException e )
                        {
                            e.printStackTrace( );
                        }
                        finally
                        {
                            lock.unlock( );
                        }

                        // print something when signal()
                        // is called on our Condition
                        System.out.printf( "Thread number %d woke up!%n", threadNumber );
                    }
                } ).start( );
            }
            finally
            {
                lock.unlock( );
            }
        }

        // acquire the ReentrantLock and call
        // Condition.signal() to wake up Thread number 3    
        lock.lock( );
        try
        {
            System.out.printf( "Waking up Thead number %d%n", 3 );

            conditions[3].signal( );
        }
        finally
        {
            lock.unlock( );
        }
    }
}

这应该打印以下内容：

启动线程号 0

开始线程号 1

启动线程号 2

启动线程号 3

启动线程号 4

醒来头号 3

3号线程醒了！

于 2012-04-15T05:15:10.407 回答