Java Semaphore使用

曾经终败给现在 2023-03-13 15:29 12阅读 0赞

**使用**

Semaphore:信号量，用于控制多个线程访问资源 void acquire() throws InterruptedException  
尝试获取一个准入的许可。如果无法获得，则线程等待，直到获取许可或者当前线程被中断

void acquireUninterruptibly() 尝试获取一个准入的标准。如果无法获得，则线程等待，不能呗线程中断。

boolean tryAcquire 尝试获取一个许可，如果成功获取则返回true，否则返回false，它不会进行等待，立即返回 boolean

tryAcquire(long timeout, TimeUnit unit) 尝试获取一个许可，直到成功获取或等待了指定的最长时间 void release() 释放许可

**Demo**

public class SemaphoreTest  implements Runnable {
        final Semaphore semaphore = new Semaphore(5);  //指定同时访问某一资源的线程数量
    
        @Override
        public void run() {
            try {
                semaphore.acquire();
                System.out.println(Thread.currentThread().getName() + " acquire,currentTime:"+getCurrentDateTime());
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName() +" done!currentTime:"+getCurrentDateTime() );
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                semaphore.release();  //释放
            }
        }
    
    
        private String getCurrentDateTime() {
            DateFormat fdt = DateFormat.getDateTimeInstance();
            return fdt.format(new Date());
        }
    
    
        public static void main(String[] args) {
            ExecutorService executor = Executors.newFixedThreadPool(20);
            SemaphoreTest st = new SemaphoreTest();
            for ( int i = 0 ; i < 20 ; i++){
                executor.submit(st);
            }
        }
    }

结果：

pool-1-thread-4 acquire,currentTime:2020-5-15 18:25:38  
pool-1-thread-3 acquire,currentTime:2020-5-15 18:25:38  
pool-1-thread-1 acquire,currentTime:2020-5-15 18:25:38  
pool-1-thread-2 acquire,currentTime:2020-5-15 18:25:38  
pool-1-thread-5 acquire,currentTime:2020-5-15 18:25:38  
pool-1-thread-2 done!currentTime:2020-5-15 18:25:40  
pool-1-thread-1 done!currentTime:2020-5-15 18:25:40  
pool-1-thread-4 done!currentTime:2020-5-15 18:25:40  
pool-1-thread-5 done!currentTime:2020-5-15 18:25:40  
pool-1-thread-3 done!currentTime:2020-5-15 18:25:40  
pool-1-thread-8 acquire,currentTime:2020-5-15 18:25:40  
pool-1-thread-7 acquire,currentTime:2020-5-15 18:25:40  
pool-1-thread-9 acquire,currentTime:2020-5-15 18:25:40  
pool-1-thread-10 acquire,currentTime:2020-5-15 18:25:40  
pool-1-thread-6 acquire,currentTime:2020-5-15 18:25:40  
pool-1-thread-6 done!currentTime:2020-5-15 18:25:42  
pool-1-thread-10 done!currentTime:2020-5-15 18:25:42  
pool-1-thread-9 done!currentTime:2020-5-15 18:25:42  
pool-1-thread-7 done!currentTime:2020-5-15 18:25:42  
pool-1-thread-8 done!currentTime:2020-5-15 18:25:42  
pool-1-thread-11 acquire,currentTime:2020-5-15 18:25:42  
pool-1-thread-12 acquire,currentTime:2020-5-15 18:25:42  
pool-1-thread-14 acquire,currentTime:2020-5-15 18:25:42  
pool-1-thread-13 acquire,currentTime:2020-5-15 18:25:42  
pool-1-thread-16 acquire,currentTime:2020-5-15 18:25:42  
pool-1-thread-11 done!currentTime:2020-5-15 18:25:44  
pool-1-thread-14 done!currentTime:2020-5-15 18:25:44  
pool-1-thread-12 done!currentTime:2020-5-15 18:25:44  
pool-1-thread-16 done!currentTime:2020-5-15 18:25:44  
pool-1-thread-13 done!currentTime:2020-5-15 18:25:44  
pool-1-thread-17 acquire,currentTime:2020-5-15 18:25:44  
pool-1-thread-18 acquire,currentTime:2020-5-15 18:25:44  
pool-1-thread-15 acquire,currentTime:2020-5-15 18:25:44  
pool-1-thread-19 acquire,currentTime:2020-5-15 18:25:44  
pool-1-thread-20 acquire,currentTime:2020-5-15 18:25:44  
pool-1-thread-15 done!currentTime:2020-5-15 18:25:46  
pool-1-thread-18 done!currentTime:2020-5-15 18:25:46  
pool-1-thread-17 done!currentTime:2020-5-15 18:25:46  
pool-1-thread-19 done!currentTime:2020-5-15 18:25:46  
pool-1-thread-20 done!currentTime:2020-5-15 18:25:46