• Latch 模式背景釋義：

• 有A、B、C、D若干個(gè)并行任務(wù)，現(xiàn)在F任務(wù)需要等ABCD全部完成之后再進(jìn)行，只要其中任一一個(gè)并發(fā)任務(wù)未執(zhí)行完F任務(wù)就阻塞或者拋出超時(shí)異常、取消任務(wù)

• 代碼翻譯：
  抽象任務(wù)接口約束類(lèi)

public abstract class Latch {

    protected int limit;

    public Latch(int limit){
        this.limit = limit;
    }

    /**
     * 阻塞當(dāng)前調(diào)用者所在線(xiàn)程，阻塞的邏輯為，如果當(dāng)前還有任務(wù)未完成則阻塞
     *
     * @throws InterruptedException
     */
    public abstract void await() throws InterruptedException;

    public abstract void await(TimeUnit unit,long time) throws InterruptedException, TimeoutException;

    /**
     * 誰(shuí)執(zhí)行完任務(wù)就將任務(wù)完成標(biāo)志減1，當(dāng)任務(wù)完成標(biāo)志為0時(shí)表示所有任務(wù)均已完成
     * 本方法為同步方法，任務(wù)線(xiàn)程執(zhí)行時(shí)需要先獲取到本接口的鎖，具體鎖住的對(duì)象為
     * limit ，當(dāng)前任務(wù)線(xiàn)程執(zhí)行完任務(wù)之后將標(biāo)志-1，同時(shí)釋放鎖
     */
    public abstract void countDown();

    /**
     * 獲取剩下未完成任務(wù)的個(gè)數(shù)
     * @return
     */
    public abstract int getUnarrived();
}

具體任務(wù)實(shí)現(xiàn)類(lèi)：

public class CountDownLatch extends Latch {

    public CountDownLatch(int limit) {
        super(limit);
    }

    @Override
    public void await() throws InterruptedException {

        synchronized (this){
            while(limit > 0){
                this.wait();
            }
        }
    }

    @Override
    public void await(TimeUnit unit, long time) throws InterruptedException, TimeoutException {
        if(time <=0){
            throw new IllegalArgumentException("the time is invalid");
        }

        //將時(shí)間轉(zhuǎn)換為納秒
        long remainingNanos = unit.toNanos(time);
        //等待任務(wù)將在endNanos 納秒后 超時(shí)
        final long endNanos = System.nanoTime() + remainingNanos;

        synchronized (this){
            while(limit > 0){
                //超時(shí)  直接拋出異常
                if(TimeUnit.NANOSECONDS.toMillis(remainingNanos) <= 0){
                    throw  new TimeoutException("time out");
                }

                //等待remainingNanos  在等待的過(guò)程中可能會(huì)被中斷，需要重新計(jì)算remainingNanos時(shí)間
                this.wait(TimeUnit.NANOSECONDS.toMillis(remainingNanos));

                //執(zhí)行線(xiàn)程中斷  時(shí)重新計(jì)算時(shí)間
                remainingNanos = endNanos - System.nanoTime();
            }
        }
    }


    @Override
    public void countDown() {

        synchronized (this){
            if(limit <= 0){
                throw new IllegalStateException("all of task has done");
            }

            limit --;
            notifyAll();
        }
    }

    @Override
    public int getUnarrived() {
        return limit;
    }
}

工作線(xiàn)程：

public class LatchTaskThread extends Thread {

    private Latch latch;

    private String programmer;

    private String transportion;

    public LatchTaskThread(Latch latch,String programmer,String transportion){
        this.latch = latch;
        this.programmer = programmer;
        this.transportion = transportion;
    }

    @Override
    public void run() {
        super.run();
        System.out.println("26--------執(zhí)行者:"+this.programmer + "  start task:"+transportion);
        try {
            TimeUnit.SECONDS.sleep(new Random().nextInt(10));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("26--------執(zhí)行者:"+this.programmer + "  finsh task:"+transportion);
        latch.countDown();

    }
}

• 測(cè)試用例：

 private void testLatch() throws InterruptedException, TimeoutException {
        latch = new CountDownLatch(4);
        new LatchTaskThread(latch,"A","Bus").start();
        new LatchTaskThread(latch,"B","Stock").start();
        new LatchTaskThread(latch,"C","Play Crad").start();
        new LatchTaskThread(latch,"D","Work").start();
        //latch.await();

        latch.await(TimeUnit.SECONDS,5);
        System.out.println("43-------所有任務(wù)均已經(jīng)完成");
    }

• 參考書(shū)籍《Java 高并發(fā)編程詳解》