自定義 aqs 的同步器，並且用 countDownLatch 測試

AbstractQueueSynchronizer 是 jdk 自帶的一個 構建 鎖 和 同步器的基類。他內部使用 CAS （compareAndSet）保證隊列的原子性, 同時利用 FIFO 隊列實現 線程間的競爭.將基礎的同步細節放在抽象類裏面。想 countDownLatch，semaphore,CyclicBarrier ,reentrantLock都是依賴 aqs 實現的。

 

實現代碼

public class SelfSynchronizedAqs {


     private static class Sync extends AbstractQueuedSynchronizer {

         @Override
         protected boolean tryAcquire(int arg) {
             if (compareAndSetState(0, 1)) {
                 setExclusiveOwnerThread(Thread.currentThread());
                 return true;
             }
             return false;
         }

         @Override
         protected boolean tryRelease(int arg) {
             int state = getState();
             if (state == 0) {
                 System.out.println("arg =  狀態錯誤");
                 return false;
             }
             setState(0);
             setExclusiveOwnerThread(null);
             return true;
         }

     }
    Sync sync = new Sync();

     public void lock(){
         sync.acquire(1);
     }

    public void unLock(){
        sync.release(1);
    }


}

具體測試代碼

/**
 * @author yueye
 * @date 2020/3/9 17:40
 * @desc
 */
public class TestSelfAqsByCountLatch {
    static int a = 0 ;


    /**
     * 比線程數量多一個原因是  務必保證 所有的線程全部執行完(a++) 操作,而且只執行一次
     *
     */
    static  int num = 31;
//    private static CyclicBarrier barrier = new CyclicBarrier(31);
    private static CountDownLatch barrier = new CountDownLatch(num);


    private static SelfSynchronizedAqs selfSynchronizedAqs = new SelfSynchronizedAqs();

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 30; i++) {
            Thread thread = new Thread((() -> {
                for (int j = 0; j < 10000; j++) {
                    increment();
                }
                try {
                    barrier.countDown();
                    barrier.await();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }));
            thread.start();
        }
        barrier.countDown();
        barrier.await();
        barrier = new CountDownLatch(num);
        // 等待一會 防止 創建線程過快
        System.out.println(System.currentTimeMillis() + "aaaaaaaaaaaaaaaaaaaaaaaaa= " + a);
        a = 0;
        int w = 0;
        for (int i = 0; i <  30; i++) {
            Thread thread = new Thread(() -> {
                for (int j = 0; j < 10000; j++) {
                    increment2();
                }
                try {
                    barrier.countDown();
                    barrier.await();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
            w ++;
            thread.start();
        }
        barrier.countDown();
        barrier.await();//等30個線程累加完畢
        System.out.println(System.currentTimeMillis() + "bbbbbbbbbbbbbbbbbbbb = " + a);
    }

    private static void increment2() {
        selfSynchronizedAqs.lock();
        a++;
        selfSynchronizedAqs.unLock();
    }

    private static void increment() {
        a++;
    }

}

輸出結果 

1583749759633aaaaaaaaaaaaaaaaaaaaaaaaa= 292263
1583749759686bbbbbbbbbbbbbbbbbbbb = 300000