Java Semaphore使用

使用

Semaphore:信號量，用於控制多個線程訪問資源 void acquire() throws InterruptedException
嘗試獲取一個准入的許可。如果無法獲得，則線程等待，直到獲取許可或者當前線程被中斷

​​​​​void acquireUninterruptibly() 嘗試獲取一個准入的標準。如果無法獲得，則線程等待，不能唄線程中斷。

boolean tryAcquire 嘗試獲取一個許可，如果成功獲取則返回true，否則返回false，它不會進行等待，立即返回 boolean

tryAcquire(long timeout, TimeUnit unit) 嘗試獲取一個許可，直到成功獲取或等待了指定的最長時間 void release() 釋放許可

 

Demo

public class SemaphoreTest  implements Runnable {
    final Semaphore semaphore = new Semaphore(5);  //指定同時訪問某一資源的線程數量

    @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();  //釋放
        }
    }


    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);
        }
    }
}

 

結果：

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