我需要互斥读取吗？ [英] Do I need a mutex for reading?

问题描述

我有一个类有一个状态（一个简单的枚举），并从两个线程访问。对于改变状态我使用互斥（boost :: mutex）。是否可以安全地检查状态（例如compare state_ == ESTABLISHED）或者在这种情况下我也必须使用互斥？换句话说，当我只想读取一个可以由另一个线程同时写入的变量时，我需要互斥量。

I have a class that has a state (a simple enum) and that is accessed from two threads. For changing state I use a mutex (boost::mutex). Is it safe to check the state (e.g. compare state_ == ESTABLISHED) or do I have to use the mutex in this case too? In other words do I need the mutex when I just want to read a variable which could be concurrently written by another thread?

推荐答案

你有两个线程，他们交换信息，是你需要一个互斥，你可能还需要一个条件等待。

You have two threads, they exchange information, yes you need a mutex and you probably also need a conditional wait.

在你的例子中（compare state_ == ESTABLISHED）线程＃2正在等待线程＃1发起连接/状态。没有互斥量或条件/事件，线程＃2必须持续轮询状态。

In your example (compare state_ == ESTABLISHED) indicates that thread #2 is waiting for thread #1 to initiate a connection/state. Without a mutex or conditionals/events, thread #2 has to poll the status continously.

线程用于提高性能（或提高响应能力），轮询通常导致减少性能，通过消耗大量的CPU或由于轮询间隔引入latencey。

Threads is used to increase performance (or improve responsiveness), polling usually results in decreased performance, either by consuming a lot of CPU or by introducing latencey due to the poll interval.

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