Re: pthread_create()'s behavor?

[Ángel González <keisial at gmail dot com>]

On 16/04/12 07:56, Hei Chan wrote:
> Hi,
>
> I am using pthread library on CentOS 5.5.
>
> I have the following code:
>
> class B {};
>
> class A {
> private:
>    std::map<long, B*> m_myMap;
> public:
>    A::A() {
>        m_myMap[0] = new B();
>        pthread_t threadID;
>        pthread_create(&threadID, NULL, start, NULL);
>    }
>    static void* start(void*) {
>        // use m_myMap[0] here, will this new thread sees everything happens before it gets created (e.g. m_myMap[0] contains the valid value)?
>        m_myMap.find(0);
>    }
> }
>
> Sometimes (~1% chance), I got a segfault at m_myMap.find(0).  Is it true that pthread_create() won't try to enforce the memory barrier to ensure all the previous writes to be globally visible?
>
> Thanks in advance.
I'm not seeing with your code (after fixes) that behavior here (which
doesn't mean it would never fail for me), but I wonder if that's really
the code that fais for you.
Is m_myMap a static parameter? Are other threads reading/writing to it?
Another thread writing m_MyMap[5] could perfectly produce a segfault on
m_myMap.find(0), and that would be expected.