小记：executor.shutdownNow无法关闭线程池，线程池卡死

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原创 2024-02-04 19:54:37 1.1k 阅读 AI 写同款· GEO 优化 ›

正确理解ExecutorService.shutdown()的优雅关闭行为在Java并发编程中，Future接口是用于表示异步计算的结果的一种方式。它使得我们可以提交一个任务到线程池中执行，并在稍后获得任务的执行结果，而不需要阻塞当前线程等待结果的返回。Future接口包含以下几个核心方法：get()：等待计算完成，并获取结果。如果任务还没有完成，则当前线程会一直等待，直到任务执行完毕。：与get()类似，但增加了超时设置，超时则抛出。：取消任务的执行。如果任务已经开始执行，根据参数决定是否中断正在执行的线程。isDone() 阅读详情

在子线程中出现没有明确退出条件，或者需要在发出中断信号后及时结束的逻辑中，一定要手动检测线程结束标志位

正确案例：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Demo {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.submit(new SubThread());
        executorService.submit(new SubThread());
        executorService.shutdown();
        try {
            if (!executorService.awaitTermination(5, TimeUnit.SECONDS)) {
                System.out.println("线程池关闭超时");
                // 触发强制关闭，将 标志位 置为 interrupted
                executorService.shutdownNow();
                if (!executorService.awaitTermination(3, TimeUnit.SECONDS)) {
                    System.out.println("线程池强制关闭失败");
                } else {
                    System.out.println("线程池强制关闭成功");
                }
            } else {
                System.out.println("线程池关闭成功");
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
}
class SubThread implements Runnable {
    @Override
    public void run() {
        while (!Thread.currentThread().isInterrupted()) {
            System.out.println(Thread.currentThread().getName());
            try {
                Thread.sleep(10000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

错误案例：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Demo {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.submit(new SubThread());
        executorService.submit(new SubThread());
        executorService.shutdown();
        try {
            if (!executorService.awaitTermination(5, TimeUnit.SECONDS)) {
                System.out.println("线程池关闭超时");
                executorService.shutdownNow();
                if (!executorService.awaitTermination(3, TimeUnit.SECONDS)) {
                    System.out.println("线程池强制关闭失败");
                } else {
                    System.out.println("线程池强制关闭成功");
                }
            } else {
                System.out.println("线程池关闭成功");
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
}
class SubThread implements Runnable {
    @Override
    public void run() {
        while (true) {
            System.out.println(Thread.currentThread().getName());
            try {
                Thread.sleep(10000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }
}