线程添加回调函数

1. 说明

有些场景下，我们需要在任务执行完成后进行一些例如通信的操作。除了在任务主体call或者run末尾添加外，我们还可以使用guava定义回调。本文主要包括以下内容：

• guava添加线程回调示例
• 回调对应源码解析
• 自定义类实现回调

2. guava回调代码示例

2.1 依赖

<dependency>
      <groupId>com.google.guava</groupId>
      <artifactId>guava</artifactId>
      <version>23.0</version>
</dependency>

2.2 代码示例

import com.google.common.util.concurrent.*;
import org.jetbrains.annotations.Nullable;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * @author pp_lan
 * @date 2024/1/22
 */
public class V2ThreadControlTest {

    public static void main(String[] args) {
        FutureCallback<Integer> callback = new FutureCallback<Integer>() {
            @Override
            public void onSuccess(@Nullable Integer aBoolean) {
                System.out.println("节点执行成功" + aBoolean);
            }

            @Override
            public void onFailure(Throwable throwable) {
                System.out.println("节点执行失败");
            }
        };

        ListeningExecutorService pool = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(128));
        try {
            ListenableFuture<Integer> future = pool.submit(() -> {
                System.out.println("节点1执行");
                return 1;
            });
            ListenableFuture<Integer> future2 = pool.submit(() -> {
                System.out.println("节点2执行");
                return 2;
            });

            Futures.addCallback(future, callback);
            Futures.addCallback(future2, callback);

            List<ListenableFuture<Integer>> futures = Arrays.asList(future, future2);
            ListenableFuture<List<Integer>> task = Futures.allAsList(futures);

            try {
                List<Integer> booleans = task.get();
                System.out.println(booleans);
            } catch (Exception e) {
                e.printStackTrace();
            }
        } finally {
            pool.shutdown();
            try {
                if (!pool.awaitTermination(10, TimeUnit.MINUTES)) {
                    pool.shutdownNow();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
}

2.3 运行结果

Connected to the target VM, address: '127.0.0.1:56043', transport: 'socket'
节点1执行
节点2执行
节点执行成功1
节点执行成功2
[1, 2]
Disconnected from the target VM, address: '127.0.0.1:56043', transport: 'socket'

Process finished with exit code 0

3. guava对应源码解析

3.1 添加监听方法

????????addListener方法中添加CallbackListener对象，该对象为一个多线程对象。添加回调监听的本质为添加一个线程持续运行，查询Future的状态及结果。

4. 模拟实现

????????为了更好理解上述源码，手写了以下代码，用以简单实现其功能，加深理解。此处主要注意以下两个点：

• listener需要创建线程持续监听
• 结果获取时候需要创建去获取然后合并，避免阻塞

4.1 类描述

类名	说明
ListenableFuture	回调接口
PackageFuture	ListenableFuture的实现类
ListeningThreadPool	线程池包装工具，包含带回调的执行方法invokeAll
V3ThreadTest	调用示例

4.2 源码

4.2.1 ListenableFuture

import java.util.concurrent.Executor;

/**
 * @author pp_lan
 * @date 2024/1/22
 */
public interface ListenableFuture<T> {

    void addListener(Runnable var1, Executor var2);

}

4.2.2 PackageFuture

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.Assert;

import java.util.concurrent.Executor;
import java.util.concurrent.Future;

/**
 * @author pp_lan
 * @date 2024/1/22
 */
public class PackageFuture<V> implements ListenableFuture {

    private static final Logger LOGGER = LoggerFactory.getLogger(PackageFuture.class);
    
    private Runnable listener;

    private Future<V> future;

    public PackageFuture(Runnable listener, Future<V> future) {
        this.listener = listener;
        this.future = future;
    }

    @Override
    public void addListener(Runnable listener, Executor executor) {
        Assert.notNull(listener, "listener不可以为空");
        Assert.notNull(executor, "executor不可以为空");
        this.listener = listener;
        try {
            executor.execute(() -> {
                while (true) {
                    if (future.isDone()) {
                        this.listener.run();
                        return;
                    }
                }
            });
        } catch (Exception e) {
            LOGGER.error("runnable listener execute error.", e);
        }
    }

    public Future<V> getFuture() {
        return future;
    }

}

4.2.3?ListeningThreadPool

import com.hz.common.bean.TimeoutException;
import com.hz.utils.thread.future.PackageFuture;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.Assert;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.*;

/**
 * @Author: pp_lan
 * @Date: 2023/12/15
 */
public class ListeningThreadPool {

    private static final Logger LOGGER = LoggerFactory.getLogger(ListeningThreadPool.class);

    private static volatile ListeningThreadPool instance;

    /**
     * queueSize设置不需要太大，不然线程数会一直为10
     */
    private ThreadPoolExecutor pool;

    private ListeningThreadPool(int parallel) {
        this.pool = new ThreadPoolExecutor(parallel, parallel, 3, TimeUnit.SECONDS, new ArrayBlockingQueue<>(1));
    }

    public <T> T submit(Callable<T> callable) {
        try {
            Future<T> future = this.pool.submit(callable);
            return future.get();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        } catch (ExecutionException e) {
            LOGGER.error("线程执行异常", e);
        }

        return null;
    }

    public <T> T submit(Callable<T> callable, Runnable listener) {

        PackageFuture<T> future = buildListenFuture(callable, listener, this.pool);

        try {
            T t = future.getFuture().get();
            return t;
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        } catch (ExecutionException e) {
            LOGGER.error("线程执行异常", e);
        }

        return null;
    }

    public <T> PackageFuture<T> buildListenFuture(Callable<T> callable, Runnable listener, ThreadPoolExecutor executor) {
        Future<T> future = executor.submit(callable);
        PackageFuture<T> baseFuture = new PackageFuture<>(listener, future);
        baseFuture.addListener(listener, executor);
        return baseFuture;
    }

    /**
     * 批量执行任务
     *
     * @param callables 任务
     * @param listeners 回调
     * @param timeout 单位秒
     * @return
     * @param <T>
     */
    public <T> List<T> invokeAll(List<Callable<T>> callables, List<Runnable> listeners, long timeout) {
        Assert.notEmpty(callables);
        Assert.notEmpty(listeners);
        Assert.isTrue(callables.size() == listeners.size(), "任务和回调数量需要一致");
        int taskNumber = callables.size();


        // 构建任务
        List<PackageFuture> futureList = new ArrayList<>();
        for (int i = 0; i < taskNumber; i++) {
            futureList.add(buildListenFuture(callables.get(i), listeners.get(i), this.pool));
        }


        long start = System.currentTimeMillis();
        Map<Integer, T> result = new TreeMap<>();
        for (int i = 0; i < taskNumber; i++) {
            int index = i;
            this.pool.execute(() -> {
                PackageFuture<T> packageFuture = futureList.get(index);
                Future<T> f = packageFuture.getFuture();
                while (true) {
                    if (!result.containsKey(index)) {
                        if (f.isDone()) {
                            try {
                                System.out.format("[%s]获取值\n", System.currentTimeMillis()/1000);
                                synchronized (this) {
                                    result.put(index, f.get());
                                }
                            } catch (Exception e) {
                                LOGGER.error("获取结果异常", e);
                            }
                        }
                    }
                }
            });
        }

        while (true) {
            if (result.size() >= taskNumber) {
                return new ArrayList<>(result.values());
            }
            if (System.currentTimeMillis() - start >= timeout * 1000) {
                for (PackageFuture packageFuture : futureList) {
                    Future f = packageFuture.getFuture();
                    if (!f.isCancelled()) {
                        f.cancel(true);    
                        LOGGER.info("取消任务");
                    }
                }
                throw new TimeoutException("取值超时");
            }
        }

    }

    public static ListeningThreadPool getInstance() {
        if (instance == null) {
            synchronized (ListeningThreadPool.class) {
                if (instance == null) {
                    instance = new ListeningThreadPool(128);
                }
            }
        }
        return instance;
    }

    public void shutdownGracefully() {
        try {
            this.pool.shutdown();
            if (!this.pool.awaitTermination(10, TimeUnit.SECONDS)) {
                this.pool.shutdownNow();
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        } finally {
            instance = null;
        }
    }

}

4.2.4?V3ThreadTest

import com.hz.utils.thread.pool.ListeningThreadPool;
import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;

/**
 * @author pp_lan
 * @date 2024/1/23
 */
public class V3ThreadTest {

    @Test
    public void test01() {
        ListeningThreadPool pool = ListeningThreadPool.getInstance();
        try {
            Callable<Integer> task = () -> {
                System.out.format("[%s]程序1运行\n", System.currentTimeMillis() / 1000);
                TimeUnit.SECONDS.sleep(2);
                System.out.format("[%s]程序1结束\n", System.currentTimeMillis() / 1000);
                return 1;
            };

            Callable<Integer> task2 = () -> {
                System.out.format("[%s]程序2运行\n", System.currentTimeMillis() / 1000);
                TimeUnit.SECONDS.sleep(1);
                System.out.format("[%s]程序2结束\n", System.currentTimeMillis() / 1000);
                return 2;
            };

            Runnable listener = () -> System.out.format("[%s]任务执行完毕\n", System.currentTimeMillis() / 1000);
            List<Integer> results = pool.invokeAll(Arrays.asList(task, task2), Arrays.asList(listener, listener), 4);
            System.out.format("[%s]%s", System.currentTimeMillis() / 1000, results);


        } finally {
            pool.shutdownGracefully();
        }

    }
}

4.3 运行结果

[1705980753]程序1运行
[1705980753]程序2运行
[1705980754]程序2结束
[1705980754]任务执行完毕
[1705980754]获取值
[1705980755]程序1结束
[1705980755]获取值
[1705980755]任务执行完毕
[1705980766][1, 2]