如何在 Java 中停止线程

Question

我正在编写一个生成 1 到 1,000 之间随机数的程序。然后，它使用一个包含三个线程的线程池来搜索更广泛的 1 到 1,000 范围内的特定数字范围。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，则向控制台显示消息。如果数字不匹配，这也会反映在发送到控制台的消息中。我试图弄清楚如何在达到目标数字后结束程序，并且即使已经找到目标也不继续分析数字。谢谢。

这是 FindIt class:

/** 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." );
            }

        }   
    }
}

这是包含主要方法的程序：

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() 并在检测到中断时让任务 return 让您的任务响应中断。
使用 ExecutorService 的 shutdownNow 方法中断当前运行任务。 shutdown 方法使执行器停止接收新任务，但让已经提交给执行器的任务运行完成。

不要为此子class 线程，您应该扩展 Runnable 或 Callable 以定义提交给 Executor 的任务。 Subclassing Thread 意味着任务分配一个 OS 线程，这是不必要的，因为实际线程已经在线程池中创建。对于此示例，由于您正在计算任务中的数字，因此使用 Callable 可能有意义。

java.util.concurrent中已有一个class就是为这种东西设计的。 API documentation for ExecutorCompletionService.

中给出了找到答案后取消任务的示例

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." );
            }

        }   
    }
}

如何在 Java 中停止线程

How to stop threads in Java

java

multithreading

thread-safety

threadpool

interruption