ForkJoin 学习使用笔记

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一灰灰blog 2022-11-02 19:46:04

文章标签 返回结果工作线程 ide 文章分类 运维

ForkJoin 学习使用笔记

Fork/Join框架是Java7提供了的一个用于并行执行任务的框架，是一个把大任务分割成若干个小任务，最终汇总每个小任务结果后得到大任务结果的框架

背景

在日常的业务需求中，经常出现的批量查询，批量写入等接口的提供，一般来说，最简单最low的方式就是写一个for循环来一次执行，但是当业务方对接口的性能要求较高时，就比较尴尬了

通常可以想到的方式是采用并发操作，首先想到可以实现的方式就是利用线程池来做

通常实现方式如下

// 1. 创建线程池

ExecutorService executorService = new ThreadPoolExecutor(3, 5, 60,
      TimeUnit.SECONDS,
      new LinkedBlockingDeque<Runnable>(10), new DefaultThreadFactory("biz-exec"),
      new ThreadPoolExecutor.CallerRunsPolicy());

// 2. 创建执行任务
List<Future<Object>> futureList = new ArrayList<>();
for(Object arg : list) {
        futureList.add(executorService.submit(new Callable<Object>() {
            @Override
            public Object call() throws Exception {
              // xxx
            }
        }));
}

// 3. 结果获取
for(Future f: futureList) {
    Object obj = f.get();
}
// 1. 创建线程池

ExecutorService executorService = new ThreadPoolExecutor(3, 5, 60,
      TimeUnit.SECONDS,
      new LinkedBlockingDeque<Runnable>(10), new DefaultThreadFactory("biz-exec"),
      new ThreadPoolExecutor.CallerRunsPolicy());

// 2. 创建执行任务
List<Future<Object>> futureList = new ArrayList<>();
for(Object arg : list) {
        futureList.add(executorService.submit(new Callable<Object>() {
            @Override
            public Object call() throws Exception {
              // xxx
            }
        }));
}

// 3. 结果获取
for(Future f: futureList) {
    Object obj = f.get();
}

用上面的这种方式并没有什么问题，我们接下来考虑的是如何使用ForkJoin框架来实现类似的功能

ForkJoin 基本知识

Fork: 将大任务拆分成若干个可以并发执行的小任务
Join: 合并所有小任务的执行结果

ForkJoin 学习使用笔记_返回结果

任务分割

ForkJoinTask : 基本任务，使用forkjoin框架必须创建的对象，提供fork,join操作，常用的两个子类 - RecursiveAction : 无结果返回的任务 - RecursiveTask : 有返回结果的任务

说明：

fork : 让task异步执行
join : 让task同步执行，可以获取返回值
ForkJoinTask 在不显示使用ForkJoinPool.execute/invoke/submit()方法进行执行的情况下，也可以使用自己的fork/invoke方法进行执行

结果合并

ForkJoinPool 执行 ForkJoinTask， - 任务分割出的子任务会添加到当前工作线程所维护的双端队列中，进入队列的头部。 - 当一个工作线程的队列里暂时没有任务时，它会随机从其他工作线程的队列的尾部获取一个任务

三中提交方式：

execute 异步，无返回结果
submit 异步，有返回结果（返回Future<T>）
invoke 同步，有返回结果（会阻塞）

使用说明

结合两个场景，给出使用姿势

1. 累加

实现从 start - end 的累加求和

首先是定义一个CountTask 来实现求和

首先是确定任务分割的阀值，当 end-start 的差值大于阀值时，将任务一分为二

public class CountTask extends RecursiveTask<Integer> {

    private int start;
    private int end;

    private static final int THRED_HOLD = 30;


    public CountTask(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum = 0;
        boolean canCompute = (end - start) <= THRED_HOLD;
        if (canCompute) { // 不需要拆分
            for (int i = start; i <= end; i++) {
                sum += i;
            }

            System.out.println("thread: " + Thread.currentThread() + " start: " + start + " end: " + end);
        } else {
            int mid = (end + start) / 2;
            CountTask left = new CountTask(start, mid);
            CountTask right = new CountTask(mid + 1, end);
            left.fork();
            right.fork();

            sum = left.join() + right.join();
        }
        return sum;
    }
}
public class CountTask extends RecursiveTask<Integer> {

    private int start;
    private int end;

    private static final int THRED_HOLD = 30;


    public CountTask(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum = 0;
        boolean canCompute = (end - start) <= THRED_HOLD;
        if (canCompute) { // 不需要拆分
            for (int i = start; i <= end; i++) {
                sum += i;
            }

            System.out.println("thread: " + Thread.currentThread() + " start: " + start + " end: " + end);
        } else {
            int mid = (end + start) / 2;
            CountTask left = new CountTask(start, mid);
            CountTask right = new CountTask(mid + 1, end);
            left.fork();
            right.fork();

            sum = left.join() + right.join();
        }
        return sum;
    }
}

调用case

@Test
public void testFork() throws ExecutionException, InterruptedException {
    int start = 0;
    int end = 200;

    CountTask task = new CountTask(start, end);
    ForkJoinPool pool = ForkJoinPool.commonPool();
    Future<Integer> ans = pool.submit(task);
    int sum = ans.get();
    System.out.println(sum);
}
@Test
public void testFork() throws ExecutionException, InterruptedException {
    int start = 0;
    int end = 200;

    CountTask task = new CountTask(start, end);
    ForkJoinPool pool = ForkJoinPool.commonPool();
    Future<Integer> ans = pool.submit(task);
    int sum = ans.get();
    System.out.println(sum);
}

输出结果：

thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] start: 51 end: 75
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 101 end: 125
thread: Thread[ForkJoinPool.commonPool-worker-1,5,main] start: 0 end: 25
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 126 end: 150
thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] start: 76 end: 100
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 151 end: 175
thread: Thread[ForkJoinPool.commonPool-worker-1,5,main] start: 26 end: 50
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 176 end: 200
20100
thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] start: 51 end: 75
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 101 end: 125
thread: Thread[ForkJoinPool.commonPool-worker-1,5,main] start: 0 end: 25
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 126 end: 150
thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] start: 76 end: 100
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 151 end: 175
thread: Thread[ForkJoinPool.commonPool-worker-1,5,main] start: 26 end: 50
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] start: 176 end: 200
20100

2. 排序

int 数组进行排序

同样先定义一个SortTask, 主要是为了演示ForkJoin的使用姿势，具体的排序和合并的逻辑比较简陋的实现了一下（这块不是重点）

public class SortTask extends RecursiveTask<List<Integer>> {

    private List<Integer> list;

    private final static int THRESHOLD = 5;

    public SortTask(List<Integer> list) {
        this.list = list;
    }

    @Override
    protected List<Integer> compute() {
        if (list.size() < THRESHOLD) {
            Collections.sort(list);

            System.out.println("thread: " + Thread.currentThread() + " sort: " + list);
            return list;
        }


        int mid = list.size() >> 1;


        SortTask l = new SortTask(list.subList(0,  mid));
        SortTask r = new SortTask(list.subList(mid, list.size()));

        l.fork();
        r.fork();

        List<Integer> left = l.join();
        List<Integer> right = r.join();

        return merge(left, right);
    }

    private List<Integer> merge(List<Integer> left, List<Integer> right) {
        List<Integer> result = new ArrayList<>(left.size() + right.size());

        int rightIndex = 0;
        for (int i = 0; i < left.size(); i++) {
            if (rightIndex >= right.size() || left.get(i) <= right.get(rightIndex)) {
                result.add(left.get(i));
            } else {
                result.add(right.get(rightIndex++));
                i -= 1;
            }
        }

        if (rightIndex < right.size()) {
            result.addAll(right.subList(rightIndex, right.size()));
        }

        return result;
    }
}
public class SortTask extends RecursiveTask<List<Integer>> {

    private List<Integer> list;

    private final static int THRESHOLD = 5;

    public SortTask(List<Integer> list) {
        this.list = list;
    }

    @Override
    protected List<Integer> compute() {
        if (list.size() < THRESHOLD) {
            Collections.sort(list);

            System.out.println("thread: " + Thread.currentThread() + " sort: " + list);
            return list;
        }


        int mid = list.size() >> 1;


        SortTask l = new SortTask(list.subList(0,  mid));
        SortTask r = new SortTask(list.subList(mid, list.size()));

        l.fork();
        r.fork();

        List<Integer> left = l.join();
        List<Integer> right = r.join();

        return merge(left, right);
    }

    private List<Integer> merge(List<Integer> left, List<Integer> right) {
        List<Integer> result = new ArrayList<>(left.size() + right.size());

        int rightIndex = 0;
        for (int i = 0; i < left.size(); i++) {
            if (rightIndex >= right.size() || left.get(i) <= right.get(rightIndex)) {
                result.add(left.get(i));
            } else {
                result.add(right.get(rightIndex++));
                i -= 1;
            }
        }

        if (rightIndex < right.size()) {
            result.addAll(right.subList(rightIndex, right.size()));
        }

        return result;
    }
}

测试case和上面基本一样，我们改用 invoke 替换上面的 submit

@Test
public void testMerge() throws ExecutionException, InterruptedException {
    List<Integer> list = Arrays.asList(100, 200, 150, 123, 4512, 3414, 3123, 34, 5412, 34, 1234, 893, 213, 455, 6, 123, 23);
    SortTask sortTask = new SortTask(list);
    ForkJoinPool pool = ForkJoinPool.commonPool();
    List<Integer> ans = pool.invoke(sortTask);
    System.out.println(ans);
}
@Test
public void testMerge() throws ExecutionException, InterruptedException {
    List<Integer> list = Arrays.asList(100, 200, 150, 123, 4512, 3414, 3123, 34, 5412, 34, 1234, 893, 213, 455, 6, 123, 23);
    SortTask sortTask = new SortTask(list);
    ForkJoinPool pool = ForkJoinPool.commonPool();
    List<Integer> ans = pool.invoke(sortTask);
    System.out.println(ans);
}

输出结果

thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] sort: [34, 3123, 3414, 4512]
thread: Thread[ForkJoinPool.commonPool-worker-1,5,main] sort: [100, 123, 150, 200]
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] sort: [34, 893, 1234, 5412]
thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] sort: [213, 455]
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] sort: [6, 23, 123]
[6, 23, 34, 34, 100, 123, 123, 150, 200, 213, 455, 893, 1234, 3123, 3414, 4512, 5412]
thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] sort: [34, 3123, 3414, 4512]
thread: Thread[ForkJoinPool.commonPool-worker-1,5,main] sort: [100, 123, 150, 200]
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] sort: [34, 893, 1234, 5412]
thread: Thread[ForkJoinPool.commonPool-worker-0,5,main] sort: [213, 455]
thread: Thread[ForkJoinPool.commonPool-worker-3,5,main] sort: [6, 23, 123]
[6, 23, 34, 34, 100, 123, 123, 150, 200, 213, 455, 893, 1234, 3123, 3414, 4512, 5412]