Semaphore in Java
作者:互联网
Semaphore
与操作系统概念中的 信号量和PV操作 类似 控制最大的并发线程数 *countdownLatch也可以实现类似功能
Example
// java program to demonstrate // use of semaphores Locks import java.util.concurrent.*; //A shared resource/class. class Shared { static int count = 0; } class MyThread extends Thread { Semaphore sem; String threadName; public MyThread(Semaphore sem, String threadName) { super(threadName); this.sem = sem; this.threadName = threadName; } @Override public void run() { // run by thread A if(this.getName().equals("A")) { System.out.println("Starting " + threadName); try { // First, get a permit. System.out.println(threadName + " is waiting for a permit."); // acquiring the lock sem.acquire(); System.out.println(threadName + " gets a permit."); // Now, accessing the shared resource. // other waiting threads will wait, until this // thread release the lock for(int i=0; i < 5; i++) { Shared.count++; System.out.println(threadName + ": " + Shared.count); // Now, allowing a context switch -- if possible. // for thread B to execute Thread.sleep(10); } } catch (InterruptedException exc) { System.out.println(exc); } // Release the permit. System.out.println(threadName + " releases the permit."); sem.release(); } // run by thread B else { System.out.println("Starting " + threadName); try { // First, get a permit. System.out.println(threadName + " is waiting for a permit."); // acquiring the lock sem.acquire(); System.out.println(threadName + " gets a permit."); // Now, accessing the shared resource. // other waiting threads will wait, until this // thread release the lock for(int i=0; i < 5; i++) { Shared.count--; System.out.println(threadName + ": " + Shared.count); // Now, allowing a context switch -- if possible. // for thread A to execute Thread.sleep(10); } } catch (InterruptedException exc) { System.out.println(exc); } // Release the permit. System.out.println(threadName + " releases the permit."); sem.release(); } } } // Driver class public class SemaphoreDemo { public static void main(String args[]) throws InterruptedException { // creating a Semaphore object // with number of permits 1 Semaphore sem = new Semaphore(1); // creating two threads with name A and B // Note that thread A will increment the count // and thread B will decrement the count MyThread mt1 = new MyThread(sem, "A"); MyThread mt2 = new MyThread(sem, "B"); // stating threads A and B mt1.start(); mt2.start(); // waiting for threads A and B mt1.join(); mt2.join(); // count will always remain 0 after // both threads will complete their execution System.out.println("count: " + Shared.count); } }
Starting A Starting B A is waiting for a permit. B is waiting for a permit. A gets a permit. A: 1 A: 2 A: 3 A: 4 A: 5 A releases the permit. B gets a permit. B: 4 B: 3 B: 2 B: 1 B: 0 B releases the permit. count: 0
标签:Java,threadName,System,Semaphore,permit,println,sem,out 来源: https://www.cnblogs.com/lnas01/p/11255978.html