如何在返回受保护的数据时使用lock_guard [英] How to use lock_guard when returning protected data

问题描述

我有一个关于使用 boost :: lock_guard （或类似的范围锁）和使用应该由锁保护的变量在 return 语句。

I have a question concerning the use of boost::lock_guard (or similar scoped locks) and using variables that should be protected by the lock in a return statement.

如何破坏本地对象和复制返回值？如何对返回值进行优化？

How is the order of destroying local objects and copying the return value? How does return value optimization affect this?

示例：

Data Class::GetData()
{
    boost::lock_guard<boost::mutex> lock(this->mMutex);
    return this->mData;
}

这是正确的（如果mData是受mMutex保护的变量）？或者我将使用一个局部作用域和一个临时的，如下面的例子所示：

Would this be correct (if mData is the variable protected by mMutex)? Or would I have to use a local scope and a temporary like shown in the example below:

Data Class::GetData()
{
    Data ret;
    {
        boost::lock_guard<boost::mutex> lock(this->mMutex);
        ret = this->mData;
    }
    return ret;
}

推荐答案

你的第一个例子是正确的。返回值是在局部变量被销毁之前，因此在释放锁之前构建的。

Just a straight return as in your first example is correct. The return value is constructed before the local variables are destroyed, and thus before the lock is released.

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