Java中常见的并发控制手段浅析

public synchronized doProcess() {
    // 同步代码块，只会有一个线程执行
}

public class Single {
  private static volatile Single instance;
  private Single() {}
  public static Single getInstance() {
      if (instance == null) {
          synchronized(Single.class) {
              if (instance == null) instance = new Single();
          }
      }
      return instance;
  }
}

public final int getAndIncrement() {
    return unsafe.getAndAddInt(this, valueOffset, 1);
}


// unsafe 实现
// cas + 自选，不断的尝试更新设置，直到成功为止
public final int getAndAddInt(Object var1, long var2, int var4) {
    int var5;
    do {
        var5 = this.getIntVolatile(var1, var2);
    } while(!this.compareAndSwapInt(var1, var2, var5, var5 + var4));

    return var5;
}

private void doSome(ReentrantReadWriteLock.WriteLock writeLock) {
    try {
        writeLock.lock();
        System.out.println("持有锁成功 " + Thread.currentThread().getName());
        Thread.sleep(1000);
        System.out.println("执行完毕! " + Thread.currentThread().getName());
        writeLock.unlock();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

@Test
public void lock() throws InterruptedException {
    ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();

    new Thread(()->doSome(reentrantReadWriteLock.writeLock())).start();
    new Thread(()->doSome(reentrantReadWriteLock.writeLock())).start();
    new Thread(()->doSome(reentrantReadWriteLock.writeLock())).start();

    Thread.sleep(20000);
}

AtomicInteger cnt = new AtomicInteger();

private void consumer(LinkedBlockingQueue<Integer> queue) {
    try {
        // 同步阻塞拿去数据
        int val = queue.take();
        Thread.sleep(2000);
        System.out.println("成功拿到: " + val + " Thread: " + Thread.currentThread());
    } catch (InterruptedException e) {
        e.printStackTrace();
    } finally {
        // 添加数据
        System.out.println("结束 " + Thread.currentThread());
        queue.offer(cnt.getAndAdd(1));
    }
}

@Test
public void blockQueue() throws InterruptedException {
    LinkedBlockingQueue<Integer> queue = new LinkedBlockingQueue<>(2);
    queue.add(cnt.getAndAdd(1));
    queue.add(cnt.getAndAdd(1));


    new Thread(() -> consumer(queue)).start();
    new Thread(() -> consumer(queue)).start();
    new Thread(() -> consumer(queue)).start();
    new Thread(() -> consumer(queue)).start();

    Thread.sleep(10000);
}

private void semConsumer(Semaphore semaphore) {
    try {
        //同步阻塞，尝试获取信号
        semaphore.acquire(1);
        System.out.println("成功拿到信号，执行: " + Thread.currentThread());
        Thread.sleep(2000);
        System.out.println("执行完毕，释放信号: " + Thread.currentThread());
        semaphore.release(1);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

@Test
public void semaphore() throws InterruptedException {
    Semaphore semaphore = new Semaphore(2);

    new Thread(() -> semConsumer(semaphore)).start();
    new Thread(() -> semConsumer(semaphore)).start();
    new Thread(() -> semConsumer(semaphore)).start();
    new Thread(() -> semConsumer(semaphore)).start();
    new Thread(() -> semConsumer(semaphore)).start();

    Thread.sleep(20_000);
}

@Test
public void countDown() throws InterruptedException {
    CountDownLatch countDownLatch = new CountDownLatch(2);

    new Thread(() -> {
        try {
            System.out.println("do something in " + Thread.currentThread());
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            countDownLatch.countDown();
        }
    }).start();

    new Thread(() -> {
        try {
            System.out.println("do something in t2: " + Thread.currentThread());
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            countDownLatch.countDown();
        }
    }).start();

    countDownLatch.await();
    System.out.printf("结束");
}

private void cyclicBarrierLogic(CyclicBarrier barrier, long sleep) {
    // 等待达到条件才放行
    try {
        System.out.println("准备执行: " + Thread.currentThread() + " at: " + LocalDateTime.now());
        Thread.sleep(sleep);
        int index = barrier.await();
        System.out.println("开始执行: " + index + " thread: " + Thread.currentThread() + " at: " + LocalDateTime.now());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

@Test
public void testCyclicBarrier() throws InterruptedException {
    // 到达两个工作线程才能继续往后面执行
    CyclicBarrier barrier = new CyclicBarrier(2);
    // 三秒之后，下面两个线程的才会输出 开始执行
    new Thread(() -> cyclicBarrierLogic(barrier, 1000)).start();
    new Thread(() -> cyclicBarrierLogic(barrier, 3000)).start();

    Thread.sleep(4000);
    // 重置，可以再次使用
    barrier.reset();
    new Thread(() -> cyclicBarrierLogic(barrier, 1)).start();
    new Thread(() -> cyclicBarrierLogic(barrier, 1)).start();
    Thread.sleep(10000);
}

private void guavaProcess(RateLimiter rateLimiter) {
    try {
        // 同步阻塞方式获取
        System.out.println("准备执行: " + Thread.currentThread() + " > " + LocalDateTime.now());
        rateLimiter.acquire();
        System.out.println("执行中: " + Thread.currentThread() + " > " + LocalDateTime.now());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

@Test
public void testGuavaRate() throws InterruptedException {
    // 1s 中放行两个请求
    RateLimiter rateLimiter = RateLimiter.create(2.0d);
    new Thread(() -> guavaProcess(rateLimiter)).start();
    new Thread(() -> guavaProcess(rateLimiter)).start();
    new Thread(() -> guavaProcess(rateLimiter)).start();
    new Thread(() -> guavaProcess(rateLimiter)).start();
    new Thread(() -> guavaProcess(rateLimiter)).start();
    new Thread(() -> guavaProcess(rateLimiter)).start();
    new Thread(() -> guavaProcess(rateLimiter)).start();

    Thread.sleep(20_000);
}