Java并发工具类（四）Semaphore

阳光穿透心脏的1/2处 2022-03-20 10:38 251阅读 0赞

## Java并发工具类（四）Semaphore ##

在J.U.C并发包中提供了一些工具类，可以供我们在日常的开发中，根据不同的情况去进行一些相关的并发控制，具体的类有：

> CountDownLatch  
> Semaphore  
> Exchanger  
> CyclicBarrier

### Exchanger ###

#### 概念 ####

`semaphore`是指信号量，是用来控制同时访问特定资源的线程总数,它通过协调各个线程,以保证合理的使用公共资源。

#### 实现 ####

public static void main(String[] args) {   
            ExecutorService service = Executors.newCachedThreadPool();
            // 同时执行的线程数2
            final Semaphore semaphore = new Semaphore(2);
            final int count = 5;  
            for (int i = 0; i < count; i++) {   
                Runnable runnable = new Runnable() {   
                    public void run() {   
                        try {   
                            semaphore.acquire();
                            System.out.println("线程:" + Thread.currentThread().getName()+"开始执行");  
                            Thread.sleep(1000);  
                        } catch (InterruptedException e) {   
                            e.printStackTrace();  
                        } finally {   
                            System.out.println("线程:" + Thread.currentThread().getName() + "执行结束");  
                            semaphore.release();  
                        }  
                    }  
                };  
                service.execute(runnable);
            }  
            service.shutdown();  
        }

#### 执行结果 ####

线程:pool-1-thread-2开始执行
    线程:pool-1-thread-1开始执行
    线程:pool-1-thread-1执行结束
    线程:pool-1-thread-4开始执行
    线程:pool-1-thread-2执行结束
    线程:pool-1-thread-3开始执行
    线程:pool-1-thread-4执行结束
    线程:pool-1-thread-5开始执行
    线程:pool-1-thread-3执行结束
    线程:pool-1-thread-5执行结束

### Semaphore特性 ###

Semaphore类的构造函数中传入的值,即为并发访问控制执行的线程数目。

### 完整代码和相关依赖请见GitHub ###

[https://github.com/dwyanewede/project-learn/tree/master/src/main/java/com/learn/demo/concurrent][https_github.com_dwyanewede_project-learn_tree_master_src_main_java_com_learn_demo_concurrent]

### 相关文章推荐 ###

Java并发工具类（一）CountDownLatch [https://blog.csdn.net/shang\_xs/article/details/87075550][https_blog.csdn.net_shang_xs_article_details_87075550]  
Java并发工具类（二）CyclicBarrier [https://blog.csdn.net/shang\_xs/article/details/87077098][https_blog.csdn.net_shang_xs_article_details_87077098]  
Java并发工具类（三）Exchanger [https://blog.csdn.net/shang\_xs/article/details/87078321][https_blog.csdn.net_shang_xs_article_details_87078321]

[https_github.com_dwyanewede_project-learn_tree_master_src_main_java_com_learn_demo_concurrent]: https://github.com/dwyanewede/project-learn/tree/master/src/main/java/com/learn/demo/concurrent
[https_blog.csdn.net_shang_xs_article_details_87075550]: https://blog.csdn.net/shang_xs/article/details/87075550
[https_blog.csdn.net_shang_xs_article_details_87077098]: https://blog.csdn.net/shang_xs/article/details/87077098
[https_blog.csdn.net_shang_xs_article_details_87078321]: https://blog.csdn.net/shang_xs/article/details/87078321