cpp主体线程本地的函数安全吗？ 如果是这样，从中调用静态函数呢？

Question

I have a lot of multithreading bugs since I introduced a second worker thread. The issues are minor and hard to trace. My latest indications point to

class MyOtherClass {
    static String defaultName;
    static String getDefaultName() {return defaultName;}
}

which is being used by:

result plainLocalFunction() {
    result r = E_SUCCESS;
    String fallbackName = MyOtherClass::getDefaultName();
    //Do other stuff with locals.
    return r;
}

I've been ages debugging this and I can only suppose that either the plainLocalFunction is shares its locals between threads or that that the call to getDefaultName() involves writing to a static variable which is not thread safe? Thanks for your time.

Answer 1

static variables inside a function would render your function not re-entrant and not thread safe.

If you have just local variables in a function then each thread stack will have its own copy of those variables and the function will be thread safe.

Answer 2

Static variables are absolutely not thread safe if you write to them (here: defaultName). Reading (if Nobody writes to it) should be okay though and I don't think calling a static function (or a dynamic one for what matters) is thread-unsafe if there are no thread-unsafe things going on in it.

Use CriticalSections (for example) to protect your variables that are used by several threads (and at least one thread might write to it).