減法計數器 CountDownLatch

// 減法 計數器
// 每次有執行緒呼叫 countDown() 數量-1 假設計數器變為0  countDownLatch.await()就會被喚醒 繼續執行
public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        // 總數是6 必須要執行任務的時候 再使用
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 1; i <= 6; i++) {
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"  Go out");
                countDownLatch.countDown();//-1
            }, String.valueOf(i)).start();
        }
        countDownLatch.await(); // 等待計數器歸零 然後再向下執行
        System.out.println("關門");
    }
}
 

加法計數器 CyclicBarrier

public class CyclicBarrierDemo {
    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {
            System.out.println("召喚神龍");
        });
        for (int i = 1; i <= 7; i++) {
            int temp = i;
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "==" + temp + "==");
                try {
                    cyclicBarrier.await(); //等待
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }, String.valueOf(i)).start();
        }

    }

}
 

Semaphore: 訊號位

public class SemaphoreDemo {
    public static void main(String[] args) {
        // 執行緒數量
        Semaphore semaphore = new Semaphore(3);
        for (int i = 1; i <= 6; i++) {
            new Thread(() -> {
                try {
                    semaphore.acquire(); // 得到
                    System.out.println(Thread.currentThread().getName() + "搶到車位");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName() + "離開車位");

                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();//釋放
                }
            }, String.valueOf(i)).start();
        }
    }
}
 

作用: 多個共享資源互斥的使用 併發限流 控制最大的執行緒數