java - 如何在Java中停止线程

Question

我正在编写一个程序，生成一个介于1到1,000之间的随机数。然后，它使用三个线程的线程池来搜索1到1,000范围内的某些数字范围。线程检查其范围内的每个数字，并将其与随机目标数字进行比较(如果匹配)，控制台上会显示消息。如果数字不匹配，这也会反射(reflect)在控制台消息中。我试图弄清楚一旦达到目标编号，如何结束程序，即使已经找到目标，也不会继续分析编号。谢谢你。

这是FindIt类:

/** fill in later */
public class FindIt extends Thread
{
    private int numToFind;
    private int numToStart;
    private int numToEnd;

    public FindIt( int nF, int nS, int nE )
    {
        numToFind = nF;
        numToStart = nS;
        numToEnd = nE;
    }

    public void run()
    {
        int counter = 0;

        int numAt = numToStart;

        for ( int i = 0; i < ( numToEnd - numToStart ) + 1; i++ )
        {
            counter++;

            if ( counter == 10 )
            {
                counter = 0;
                Thread.yield();
            }

            if ( numAt++ == numToFind )
            {
                System.out.println( "The target number, " + numToFind + ", has been found by " + Thread.currentThread().getName() + "." );
            }

            else
            {
                System.out.println( Thread.currentThread().getName() + " has analyzed the number " + ( numAt - 1 ) + " - not the target number." );
            }

        }   
    }
}

这是带有主要方法的程序:

import java.util.Random; //imports Java's Random class
import java.util.concurrent.*;

/** fill in later */
public class NumberSearch
{
    public static void main( String [] args )
    {
        Random r = new Random(); //creates an instance of the Random class
        int randomNum = r.nextInt( 1001 ); //declares the integer randomNum and initilizes it to be a random interger in the range 0 inclusive to 1001 exclusive

        ExecutorService executor = Executors.newFixedThreadPool( 3 );

        FindIt find1 = new FindIt( randomNum, 0, 349);
        FindIt find2 = new FindIt( randomNum, 350, 699);
        FindIt find3 = new FindIt( randomNum, 700, 1000);

        executor.execute( find1 );
        executor.execute( find2 );
        executor.execute( find3 );

        executor.shutdown();
    }
}

Answer 1

需要两件事:

通过检查Thread.currentThread().isInterrupted()并使任务在检测到中断时返回，使您的任务对中断做出响应。

使用ExecutorService的shutdownNow方法来中断当前正在运行的任务。 shutdown方法使执行程序停止接收新任务，但使已经提交给执行程序的任务运行完毕。

为此，不要将Thread子类化，您应该扩展Runnable或Callable以便定义提交给Executor的任务。对线程进行子类化意味着任务分配了一个OS线程，这是不必要的，因为实际的线程已经在线程池中创建了。对于此示例，由于您要在任务中计算数字，因此使用Callable可能有意义。

java.util.concurrent中有一个用于此类事情的现有类。一旦找到答案，取消任务的示例在 API documentation for ExecutorCompletionService中给出。

FindIt更改为检测中断:

public class FindIt implements Runnable
{
    private int numToFind;
    private int numToStart;
    private int numToEnd;

    public FindIt( int nF, int nS, int nE )
    {
        numToFind = nF;
        numToStart = nS;
        numToEnd = nE;
    }

    public void run()
    {
        int counter = 0;

        int numAt = numToStart;

        for ( int i = 0; i < ( numToEnd - numToStart ) + 1; i++ )
        {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println(Thread.currentThread().getName() 
                + " detected interruption, exiting");
                return;
            }
            counter++;

            if ( counter == 10 )
            {
                counter = 0;
                Thread.yield();
            }

            if ( numAt++ == numToFind )
            {
                System.out.println( "The target number, " + numToFind + ", has been found by " + Thread.currentThread().getName() + "." );
            }

            else
            {
                System.out.println( Thread.currentThread().getName() + " has analyzed the number " + ( numAt - 1 ) + " - not the target number." );
            }

        }   
    }
}