aqs同步组件

　技术信号量用来控制能够同时访问某特定资源的活动的数量，或者同时执行某一给定操作的数据。计数信号量可以用来实现资源池或者给一个容器限定边界。

　　信号量维护了一个许可集，许可的初始量通过构造函数传递给Semaphore。活动能够获取许可，并在使用之后释放许可，如果没有可用的许可，acquire方法会被阻塞，直到有可用的为止。每个release方法添加一个许可，从而可能释放一个正在阻塞的获取者

• Semaphore(int permits，boolean fair) 设置公平还是不公平的。
• Semaphore(int permits)：创建具有给定许可数和非公平设置的Semaphore
• int availablePermits() ：返回此信号量中当前可用的许可证数。
• int getQueueLength()：返回正在等待获取许可证的线程数。
• boolean hasQueuedThreads() ：是否有线程正在等待获取许可证。
• void reducePermits(int reduction) ：减少reduction个许可证。是个protected方法。
• Collection getQueuedThreads() ：返回所有等待获取许可证的线程集合。是个protected方法。

• SemaphoreDemo

  package com.mmall.concurrency.example.AQS.semaphore;
  
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Semaphore;
  
  public class SemaphoreDemo {
      public static void main(String[] args) {
          Semaphore semaphore=new Semaphore(3);
  
          Workers worker=new Workers("小黄",semaphore);
          Workers worker1=new Workers("小蓝",semaphore);
          Workers worker2=new Workers("小白",semaphore);
          Workers worker3=new Workers("小子",semaphore);
          Workers worker4=new Workers("小绿",semaphore);
          Workers worker5=new Workers("小黑",semaphore);
          Workers worker6=new Workers("小红",semaphore);
          ExecutorService executorService=Executors.newCachedThreadPool();
          executorService.execute(worker);
          executorService.execute(worker1);
          executorService.execute(worker2);
          executorService.execute(worker3);
          executorService.execute(worker4);
          executorService.execute(worker5);
          executorService.execute(worker6);
      }
  }
  

• Workers

  package com.mmall.concurrency.example.AQS.semaphore;
  
  import lombok.extern.slf4j.Slf4j;
  
  import java.util.concurrent.Semaphore;
  @Slf4j
  public class Workers implements Runnable {
      private String name;
      private Semaphore semaphore;
  
      public Workers(String name, Semaphore semaphore) {
          this.name = name;
          this.semaphore = semaphore;
      }
  
      @Override
      public void run() {
          try {
              semaphore.acquire();
              System.out.println(String.format("%s拿到了指令许可", name));
              Thread.sleep(3000);
              System.out.println(String.format("%s工作结束，还剩%s没有拿到指令许可", name, semaphore.getQueueLength()));
          }catch (Exception e){
              log.info("error{}",e);
          }
          semaphore.release();
      }
  }