Question

import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

class Task implements Callable<String> {
    public String call() throws Exception {
        String s = "initial";
        try {
            System.out.println("Started..");
            /*for (int i=0;i<10000;i++) {
                if (i % 2 == 0) {
                    System.out.println("Even");
                }
            }*/
            boolean flag = true;
            while(flag) {

            }
            System.out.println("Finished!");
            s = "Done";
        }
        catch (RuntimeException e) {
            s = "RuntimeException";
        }
        catch (Exception e) {
            s = "Exception";
        }
        finally {

        }
        return s;
    }
}

public class ExecutorServiceTest {

    public static void main(String[] args) throws Exception {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        List<Future<String>> result = executor.invokeAll(Arrays.asList(new Task()), 5, TimeUnit.SECONDS);
        executor.shutdown();
        Iterator<Future<String>> iter = result.iterator();
        while (iter.hasNext()) {
            System.out.println("Came here");
            Future<String> fut = iter.next();
            System.out.println(fut.get());
        }
    }
}

有没有办法可以阻止线程执行无限循环？

Answer 1

是的，您可以将flag（或逻辑&&）替换为!Thread.currentThread().isInterrupted()。

这样，当任务为canceled,时，循环将被终止。

循环看起来像这样：

while(!Thread.currentThread().isInterrupted() && flag) {
  /* Do work. */
}

使用应该是这样的：

ExecutorService executor = Executors.newSingleThreadExecutor();
Future<String> task = executor.submit(new Task());
String str;
try {
  str = task.get(5, TimeUnit.SECONDS);
} finally {
  task.cancel(true);
}

Answer 2

考虑在synchronized (this) { this.wait() }内使用sleep代替call()，然后在外部设置布尔flag（可能直接或通过flag()方法;通过直接访问确保您的标志变量为volatile）调用task.notifyAll()以唤醒休眠线程（确保您的任务对象是本地变量而不是匿名，以便您可以调用方法它，并在Task）内标记一个类属性。

它也会更有效率，因为循环浪费不必要的循环 - 确切的机制被称为'保护块'（http://java.sun.com/docs/books/tutorial/essential/concurrency/guardmeth.html）。当您从等待中醒来时，请测试标志变量，以确保它已设置。

编辑：更仔细地查看原始问题，并使用现有的代码和原则创建了一个示例（有一种方法可以让猫皮肤化:)）。试试这个 - 这里的循环由于当前线程的中断状态而退出，该状态因超时而被取消：

package ett;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

class Task implements Callable<String> {
    public String call() throws Exception {
        String s = "initial";
        System.out.println("Started..");
        for (int i=0;;i++) {
            if (i % 2 == 0) {
                System.out.println("Even");
            }
            Thread.yield();
            if (Thread.interrupted()) break;
        }
        System.out.println("Finished!");
        s = "Done";

        return s;
    }
}

public class ExecutorServiceTest {

    public static void main(String[] args) throws Exception {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        List<Future<String>> result = executor.invokeAll(Arrays.asList(new Task()), 1, TimeUnit.SECONDS);
        executor.shutdown();

        System.out.println("came here");

        for (Future<String> f : result) {
            try {
                System.out.println(f.get());
            } catch (CancellationException e) {
                e.printStackTrace();
            }
        }
    }
}

在ExecutorService任务中停止无限循环

2 个答案: