JUC并发编程 共享模式之工具 线程池 JDK 提供的线程池工具类 -- ThreadPoolExecutor（关闭线程池: shutdownshutdownNow）

Posted 2021-10-21 Z && Y

1. 关闭线程池

---

1.1 shutdown

/*
线程池状态变为 SHUTDOWN
- 不会接收新任务
- 但已提交任务会执行完
- 此方法不会阻塞调用线程的执行
*/
void shutdown();

测试代码:

package com.tian;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

@Slf4j(topic = "c.TestShutDown")
public class TestShutDown {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService pool = Executors.newFixedThreadPool(2);

        Future<Integer> result1 = pool.submit(() -> {
            log.debug("task 1 running...");
            Thread.sleep(1000);
            log.debug("task 1 finish...");
            return 1;
        });

        Future<Integer> result2 = pool.submit(() -> {
            log.debug("task 2 running...");
            Thread.sleep(1000);
            log.debug("task 2 finish...");
            return 2;
        });

        Future<Integer> result3 = pool.submit(() -> {
            log.debug("task 3 running...");
            Thread.sleep(1000);
            log.debug("task 3 finish...");
            return 3;
        });

        log.debug("shutdown");
        pool.shutdown();
        log.debug("other....");
    }
}

运行结果:

已提交任务（包括阻塞队列里面的线程）会执行完后才关闭了线程池

---

1.2 shutdownNow

/*
线程池状态变为 STOP
- 不会接收新任务
- 会将队列中的任务返回
- 并用 interrupt 的方式中断正在执行的任务
*/
List<Runnable> shutdownNow();

示例代码:

package com.tian;

import lombok.extern.slf4j.Slf4j;

import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

@Slf4j(topic = "c.TestShutDown")
public class TestShutDown {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService pool = Executors.newFixedThreadPool(2);

        Future<Integer> result1 = pool.submit(() -> {
            log.debug("task 1 running...");
            Thread.sleep(1000);
            log.debug("task 1 finish...");
            return 1;
        });

        Future<Integer> result2 = pool.submit(() -> {
            log.debug("task 2 running...");
            Thread.sleep(1000);
            log.debug("task 2 finish...");
            return 2;
        });

        Future<Integer> result3 = pool.submit(() -> {
            log.debug("task 3 running...");
            Thread.sleep(1000);
            log.debug("task 3 finish...");
            return 3;
        });

        log.debug("shutdown");
        List<Runnable> runnables = pool.shutdownNow();
        log.debug("other.... {}", runnables);
    }
}

运行结果:

发现立即关闭了线程池，返回的结果是没有执行完的任务。你可以后面在调用相关的方法重新去执行没有完成的任务

---

1.3 其它方法

// 不在 RUNNING 状态的线程池，此方法就返回 true
boolean isShutdown();
// 线程池状态是否是 TERMINATED
boolean isTerminated();
// 调用 shutdown 后，由于调用线程并不会等待所有任务运行结束，
// 因此如果它想在线程池 TERMINATED 后做些事情，可以利用此方法等待
boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException;

---

---