OpenSSL and multi-threads

Question

I've been reading about the requirement that if OpenSSL is used in a multi-threaded application, you have to register a thread identification function (and also a mutex creation function) with OpenSSL.

On Linux, according to the example provided by OpenSSL, a thread is normally identified by registering a function like this:

static unsigned long id_function(void){
    return (unsigned long)pthread_self();
}

pthread_self() returns a pthread_t, and this works on Linux since pthread_t is just a typedef of unsigned long.

On Windows pthreads, FreeBSD, and other operating systems, pthread_t is a struct, with the following structure:

struct {
    void * p;                   /* Pointer to actual object */
    unsigned int x;             /* Extra information - reuse count etc */ 
}

This can't be simply cast to an unsigned long, and when I try to do so, it throws a compile error. I tried taking the void *p and casting that to an unsigned long, on the theory that the memory pointer should be consistent and unique across threads, but this just causes my program to crash a lot.

What can I register with OpenSSL as the thread identification function when using Windows pthreads or FreeBSD or any of the other operating systems like this?

Also, as an additional question:
Does anyone know if this also needs to be done if OpenSSL is compiled into and used with QT, and if so how to register QThreads with OpenSSL? Surprisingly, I can't seem to find the answer in QT's documentation.

Answer 1

I only can answer the Qt part. Use QThread::currentThreadId(), or even QThread::currentThread() as the pointer value should be unique.