有关servlet多线程环境的问题 [英] Question regarding multi-threaded environment of servlet

问题描述

如果有servlet，则在servlet容器(例如Websphere)内.该servlet由某些线程执行.我想问一下，线程共享什么?它们之间如何共享变量?

If there is a servlet, inside a servlet container such as Websphere. The servlet are executed by some threads. I would like to ask, what does the threads share? How variables are shared between them?

它们是否具有以下变量的本地副本?

Do they have a local copy of the following variables?

1)私有/受保护/公共的最终信号灯许可=新的信号灯(50);

1) private/protected/public final Semaphore permits = new Semaphore(50);

2)私有/受保护/公共最终静态信号量许可=新的信号量(50);

2) private/protected/public final static Semaphore permits = new Semaphore(50);

3)私有/受保护/公共信号灯许可=新信号灯(50);

3) private/protected/public Semaphore permits = new Semaphore(50);

4)私有/受保护/公共静态信号量许可=新的信号量(50);

4) private/protected/public static Semaphore permits = new Semaphore(50);

我应该如何声明信号量，以便可以使用信号量来控制它们?我不希望他们给每个人一个信号量的副本.谢谢.

How should I declare the semaphore so that I can use semaphore to control them? I don't want them to have each of them a copy of the semaphore. Thanks.

推荐答案

每个线程都有自己的堆栈，但是所有线程共享相同的内存空间.考虑到这一点，一个实例可以在多个线程之间共享，因此可以共享其状态/属性.因此，我们需要使用同步或类似技术来照顾状态.

Each thread has its own stack, but all share the same memory space. With that in mind, a single instance can be shared, and so its state/properties, among multiple threads. Hence, we need to take care of state using synchronisation or similar techniques.

如果您定义一个静态变量，或者将使用servlet的一个实例-这很有可能，但不能保证，那么对于所有线程来说都是相同的.

If you define a static variable or a single instance of servlet will be used -- which is highly likely but no guarantee, then it would be the same for all threads.

尽管如此，您应该创建一个类，该类提供要在servlet中使用的单例信号量.这样，无论什么情况，servlet实例都将使用一个和相同的信号量对象.

Nonetheless, you should create a class which provide a singleton semaphore to be used in servlet. That way servlet instances will be using the one and the same semaphore object, no matter what.

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