1.1.6 方法getQueueLength()和hasQueuedThreads()

方法getQueueLength()的作用是取得等待许可的线程个数。

方法hasQueuedThreads()的作用是判断有没有线程在等待这个许可。

这两个方法通常都是在判断当前有没有等待许可的线程信息时使用。

创建测试用的项目twoMethodTest，类MyService.java代码如下：

        package myservice;
        import java.util.concurrent.Semaphore;
        public class MyService {
            private Semaphore semaphore = new Semaphore(1);
            public void testMethod() {
                try {
                    semaphore.acquire();
                    Thread.sleep(1000);
                    System.out.println("还有大约" + semaphore.getQueueLength() + "个线程在等待");
                    System.out.println("是否有线程正在等待信号量呢？" + semaphore.
                    hasQueuedThreads());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            }
        }

类MyThread.java代码如下：

        package extthread;
        import myservice.MyService;
        public class MyThread extends Thread {
            private MyService myService;
              public MyThread(MyService myService) {
                  super();
                  this.myService = myService;
              }
              @Override
              public void run() {
                  myService.testMethod();
              }
          }

类Run.java代码如下：

        package test.run;
        import myservice.MyService;
        import extthread.MyThread;
        public class Run {
            public static void main(String[] args) {
                MyService service = new MyService();
                MyThread firstThread = new MyThread(service);
                firstThread.start();
                MyThread[] threadArray = new MyThread[4];
                for (int i = 0; i < 4; i++) {
                    threadArray[i] = new MyThread(service);
                    threadArray[i].start();
                }
            }
        }

程序运行后的效果如图1-14所示。线程的个数呈递减的状态。

图1-14 运行结果