Concurrent - Semaphore - acquire(int permits)

原创转载请注明出处：http://agilestyle.iteye.com/blog/2342898

有参方法acquire(int permits)表示每调用1次此方法，就使用Semaphore中的x个permits

Service.java

package org.fool.java.concurrent.semaphore.acquire;import java.util.concurrent.Semaphore;public class Service {private Semaphore semaphore = new Semaphore(10);public void testMethod() {try {semaphore.acquire(2);System.out.println(Thread.currentThread().getName() + " begin timer=" + System.currentTimeMillis());int sleepValue = 5000;System.out.println(Thread.currentThread().getName() + " stop " + (sleepValue / 1000) + " sec");Thread.sleep(sleepValue);System.out.println(Thread.currentThread().getName() + " end timer=" + System.currentTimeMillis());semaphore.release(2);} catch (InterruptedException e) {e.printStackTrace();}}
}

Note:

private Semaphore semaphore = new Semaphore(10);

定义10个permits，每次执行semaphore.acquire(2);消耗掉2个，所以10/2=5，说明同一时间只允许5个线程执行acquire()和release()之间的代码。 

ThreadA.java

package org.fool.java.concurrent.semaphore.acquire;public class ThreadA implements Runnable {private Service service;public ThreadA(Service service) {this.service = service;}@Overridepublic void run() {service.testMethod();}
}

SemaphoreTest.java

package org.fool.java.concurrent.semaphore.acquire;public class SemaphoreTest {public static void main(String[] args) throws InterruptedException {Service service = new Service();for (int i = 0; i < 10; i++) {new Thread(new ThreadA(service)).start();}}
}

Run

如果多次调用Semaphore的release()或release(int)方法时，还可以动态增加permits的个数。

package org.fool.java.concurrent.semaphore.acquire;import java.util.concurrent.Semaphore;public class SemaphoreTest2 {public static void main(String[] args) {try {Semaphore semaphore = new Semaphore(5);semaphore.acquire();semaphore.acquire();semaphore.acquire();semaphore.acquire();semaphore.acquire();System.out.println(semaphore.availablePermits());   // outputs 0semaphore.release();semaphore.release();semaphore.release();semaphore.release();semaphore.release();semaphore.release();System.out.println(semaphore.availablePermits());   // outputs 6semaphore.release(4);System.out.println(semaphore.availablePermits());   // outputs 10} catch (InterruptedException e) {e.printStackTrace();}}
}

Note:

Semaphore semaphore = new Semaphore(5);

 定义的5并不是最终的permits数量，仅仅是初始的状态值。