Easy Java

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Fork-Join框架

递归处理一个可以折分成多个子任务的任务。

示例代码：

public class ForkJoinSum extends RecursiveTask<Integer> {    public ForkJoinSum(int[] group, int from, int to) {        _group = group;        _from = from;        _to = to;    }    private int[] _group;    private int _from;    private int _to;    protected Integer compute() {        if (_to - _from <= 2) {            int back = 0;            for (int i = _from; i <= _to; i++)                back += _group[i];            return back;        } else {            int mid = (_from + _to) / 2;            ForkJoinSum c1 = new ForkJoinSum(_group, _from, mid);            ForkJoinSum c2 = new ForkJoinSum(_group, mid, _to);            invokeAll(c1, c2);            return c1.join() + c2.join();        }    }}

        int[] a={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20};        ForkJoinPool p= new ForkJoinPool();        ForkJoinSum task = new ForkJoinSum(a,0,19);        p.invoke(task);        System.out.println(task.join());

同步器

CyclicBarrier

对多个任务进行分步，只有所有任务的某一步骤完成时，才能进入下一步骤，和.net中的Barrier一样。
示例代码：

public class CyclicBarrierTask implements Runnable {    public CyclicBarrierTask(CyclicBarrier barrier)    {        _barrier = barrier;    }    private CyclicBarrier _barrier;    public void run() {        long tid = Thread.currentThread().getId();        try {            System.out.println(tid + ": Step 1");            _barrier.await();            System.out.println(tid + ": Step 2");            _barrier.await();            System.out.println(tid + ": Step 3");            _barrier.await();            System.out.println(tid + ": Step 4");            _barrier.await();            System.out.println(tid + "End");        } catch (BrokenBarrierException | InterruptedException e) {            System.out.println(tid + ": Exception take with " + e.getMessage());        }    }}

        ExecutorService pool = Executors.newCachedThreadPool();        CyclicBarrier barrier=new CyclicBarrier(4);        for(int i=0;i<4;i++)        {            pool.submit(new CyclicBarrierTask(barrier));        }

CountDownLatch

计数为0时执行，只能执行一次。

Exchanger

兄弟线程可以交换数据。

Semaphore

限定同时运行的任务数。示意代码如下：

        final Semaphore semp = new Semaphore(5);        for(int i=0;i<n;i++)        Runnable run = new Runnable() {                public void run() {                    try {                        // 获取许可                        semp.acquire();                        //...                        // 访问完后，释放                        semp.release();                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                }

需要注意的是不要释放多次semp，需要配对使用。

SynchronousQueue

线程间共享数据，没有缓冲区。一个线程put即会阻塞，直到有线程take；一个线程take也会阻塞，直到有线程put。
示例代码

public class SynchronousQueueTest {    private static SynchronousQueue<Integer> _syncQueue = new SynchronousQueue<>();    public static Runnable getPutTask() {        return new Runnable() {            @Override            public void run() {                try {                    Thread.sleep(2000);                    _syncQueue.put(2);                } catch (InterruptedException e) {                    System.out.println(e.getMessage());                }            }        };    }    public static Runnable getTakeTask(){        return new Runnable() {            @Override            public void run() {                try {                    Thread.sleep(1000);                    System.out.println("take num is :"+_syncQueue.take());                } catch (InterruptedException e) {                    System.out.println(e.getMessage());                }            }        };    }}

ExecutorService exec = Executors.newCachedThreadPool();        exec.submit(SynchronousQueueTest.getPutTask());        exec.submit(SynchronousQueueTest.getTakeTask());

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