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java線程池ExecutorService超時(shí)處理小結(jié)

更新時(shí)間：2024年09月26日 10:23:04 作者：小百菜

使用ExecutorService時(shí),設(shè)置子線程執(zhí)行超時(shí)是一個(gè)常見需求,本文就來詳細(xì)的介紹一下ExecutorService超時(shí)的三種方法,感興趣的可以了解一下

方式一、使用 future.get() 來監(jiān)聽超時(shí)取消

這種辦法看似能解決問題，但是當(dāng)任務(wù)累積處理不過來時(shí)，會(huì)漏執(zhí)行。
比如下面的例子，就實(shí)際只會(huì)執(zhí)行一個(gè)子線程。

package com.study;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.*;

public class Test {
    private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    private static final ExecutorService threadPool = Executors.newFixedThreadPool(1);

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 10; i++) {
            Future<?> future = threadPool.submit(new Runnable() {
                @Override
                public void run() {
                    try {
                        System.out.println(LocalDateTime.now().format(formatter));
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                        // e.printStackTrace();
                    }
                }
            });
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        future.get(3, TimeUnit.SECONDS);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } catch (ExecutionException e) {
                        e.printStackTrace();
                    } catch (TimeoutException e) {//超時(shí)異常
                        future.cancel(true); // 超時(shí)后取消任務(wù)
                    }
                }
            }).start();
        }
    }
}

方式二、在子線程內(nèi)部，超時(shí)后去發(fā)送中斷信號(hào)

package com.study;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.*;

public class Test {
    private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    private static final ExecutorService threadPool = Executors.newFixedThreadPool(1);
    private static final ScheduledExecutorService timeoutExecutor = new ScheduledThreadPoolExecutor(1);//監(jiān)聽超時(shí)，這個(gè)數(shù)量要和線程池?cái)?shù)量相同

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 10; i++) {
            // int delay = 3;
            int delay = i + 1;
            threadPool.submit(new Runnable() {
                @Override
                public void run() {
                    ScheduledFuture<?> schedule = null;
                    try {
                        Thread thread = Thread.currentThread();
                        // 啟動(dòng)一個(gè)定時(shí)器，如果任務(wù)執(zhí)行超過3秒則中斷當(dāng)前線程
                        schedule = timeoutExecutor.schedule(() -> {
                            thread.interrupt(); // 中斷當(dāng)前正在執(zhí)行的任務(wù)
                        }, delay, TimeUnit.SECONDS);
                        System.out.println(LocalDateTime.now().format(formatter));
                        Thread.sleep(5000);
                        // FileOutputStream fos = new FileOutputStream("d:/test.txt" + k);
                        // for (int j = 0; j < 1000000; j++) {
                        //     fos.write("123".getBytes());
                        // }
                        // fos.close();
                    } catch (InterruptedException e) {
                        // e.printStackTrace();
                    } finally {
                        if (schedule != null) {
                            //取消任務(wù)
                            schedule.cancel(true);
                        }
                    }
                }
            });
        }
    }
}

這里其實(shí)還是有問題，把 Thread.sleep(5000);改成注釋的io阻塞，還是要等線程執(zhí)行結(jié)束后才會(huì)取消線程執(zhí)行。

所以單純使用 future 是實(shí)現(xiàn)不了這個(gè)場景的邏輯的。

timeoutExecutor 數(shù)量和線程池?cái)?shù)量要一致的原因如下示例。

package com.study;

import java.time.LocalDateTime;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class ScheduledExecutorServiceExample {

    private static final ScheduledExecutorService timeoutExecutor = new ScheduledThreadPoolExecutor(2);

    public static void main(String[] args) throws InterruptedException {
        // 調(diào)用schedule方法兩次
        scheduleTask("Task 1");
        scheduleTask("Task 2");
        scheduleTask("Task 3");
    }

    private static void scheduleTask(String taskName) {
        timeoutExecutor.schedule(() -> {
            System.out.println(taskName + " started at: " + LocalDateTime.now());
            try {
                // 模擬任務(wù)執(zhí)行
                Thread.sleep(2000); // 假設(shè)每個(gè)任務(wù)執(zhí)行2秒
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }, 3, TimeUnit.SECONDS);
    }
}

方式三、自己定義鎖來實(shí)現(xiàn)

package com.study;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.*;

public class Test {
    private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    private static final ExecutorService threadPool = Executors.newFixedThreadPool(16);//這里不能設(shè)置為1了，這里已經(jīng)不是用來控制并發(fā)數(shù)量了，只是為了重復(fù)利用線程
    private static final ScheduledExecutorService timeoutExecutor = new ScheduledThreadPoolExecutor(1);//監(jiān)聽超時(shí)，這個(gè)數(shù)量要和線程池?cái)?shù)量相同

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 10; i++) {
            Thread.sleep(50);
            // int delay = 3;
            int delay = i + 1;
            int k = i;
            threadPool.submit(new Runnable() {
                @Override
                public void run() {
                    ScheduledFuture<?> schedule = null;
                    try {
                        ThreadPool.awaitThread();
                        // 啟動(dòng)一個(gè)定時(shí)器，如果任務(wù)執(zhí)行超過3秒則中斷當(dāng)前線程
                        // timeoutExecutor如果只有一個(gè)線程池，這里面的代碼片段會(huì)阻塞，上一個(gè)線程在這里的代碼片段執(zhí)行完后，當(dāng)前線程才會(huì)執(zhí)行這里的代碼片段，
                        // 但是影響不大，因?yàn)檫@里的代碼片段只是釋放動(dòng)作，一瞬間就會(huì)執(zhí)行完，所以影響不大，
                        // 如果其他場景這里阻塞時(shí)間比較久，那么timeoutExecutor線程大小要和threadPool線程大小一致。
                        schedule = timeoutExecutor.schedule(() -> {
                            System.out.println("釋放1");
                            ThreadPool.releaseThread();
                        }, delay, TimeUnit.SECONDS);
                        System.out.println("【" + Thread.currentThread().getName() + "】" + LocalDateTime.now().format(formatter));
                        Thread.sleep(5000);
                        // FileOutputStream fos = new FileOutputStream("d:/test.txt" + k);
                        // for (int j = 0; j < 1000000; j++) {
                        //     fos.write("123".getBytes());
                        // }
                        // fos.close();
                    } catch (Exception e) {
                        System.out.println("異常");
                    } finally {
                        if (schedule != null) {
                            //cancel返回true任務(wù)還未執(zhí)行，需要取消任務(wù)
                            if (schedule.cancel(true)) {
                                System.out.println("釋放2");
                                ThreadPool.releaseThread();
                            }
                        }
                    }
                }
            });
        }
    }
}

package com.study;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 線程池
 */
public class ThreadPool {
    private static final int MAX_POOL_SIZE = 1; // 最大線程數(shù)，控制并發(fā)數(shù)量
    private static int totalThread = 0; // 總線程數(shù)
    private static final Lock lock = new ReentrantLock(true);
    private static final Condition notice = lock.newCondition();

    /**
     * 從線程池獲取線程
     */
    public static boolean awaitThread() {
        lock.lock();
        try {
            // 嘗試從線程池中獲取線程
            if (totalThread < MAX_POOL_SIZE) {
                totalThread++;
                return true;
            }
            // 線程已到達(dá)最大線程數(shù)，等待歸還線程，最長等待1小時(shí)，await()會(huì)釋放當(dāng)前線程的鎖
            if (notice.await(1, TimeUnit.HOURS)) {
                totalThread++;
                return true;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
        return false;
    }


    /**
     * 釋放線程到線程池
     */
    public static void releaseThread() {
        lock.lock();
        try {
            totalThread--;
            // 通知有空閑，signal()會(huì)喚醒其中一個(gè)await()線程
            notice.signal();
        } finally {
            lock.unlock();
        }
    }

}

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