为什么信号量中的acquire（）方法不必同步？ [英] Why does the acquire() method in Semaphores not have to be synchronized?

问题描述

我正在使用Java进入Semaphores并正在阅读本文 http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/Semaphore.html 。我唯一没有得到的是为什么在同步的上下文中没有使用acquire（）方法。查看以上网站的示例：

I am getting into Semaphores in Java and was reading this article http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/Semaphore.html . The only thing I don't get is why the acquire() method is not used in a synchronized context. Looking at the example from the above webiste:

他们创建信号量：

private Semaphore semaphore = new Semaphore(100);

并获得这样的许可证：

semaphore.acquire();

现在，两个或更多线程是否有可能尝试同时获取（）时间？如果是这样，计数会有一点问题。

Now, wouldn't it be possible that two or more threads try to acquire() at the same time? If so, there would be a little problem with the count.

或者，信号量本身是否处理同步？

Or, does the semaphore itself handle the synchronization?

推荐答案

或者，信号量本身是否处理同步？

Or, does the semaphore itself handle the synchronization?

是的，基本上就是这样。信号量是线程安全的，如 javadoc < a>：

Yes that's basically it. Semaphores are thread safe as explained in the javadoc:

内存一致性效果：在调用release方法（如release（）之前）中的一个线程中的操作发生在操作之前跟随一个成功的获取方法，如另一个线程中的acquire（）。

Memory consistency effects: Actions in a thread prior to calling a "release" method such as release() happen-before actions following a successful "acquire" method such as acquire() in another thread.

<$ c $中对象的大多数操作c> java.util.concurrent 包是线程安全的。更多详细信息在包javadoc 。

Most operations on the objects in the java.util.concurrent package are thread safe. More details are provided at the very bottom of the package javadoc.

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