Re: Two-step object initialization (using a thread)

Hi!

vl106 schrieb:


Ok, apart from your problem: replace the heap object with a stack based
object:

int main() {
    int val(0);
    C aC(&val);
    thread(&val);
    aC.f();
}

Regarding your problem: you do not ensure the thread runs before the
aC.f() call. The thread might have been created and started, but not yet
scheduled for CPU time. That means you "threadsafe_begin" in C::f will
enter although val is not initialized. Further C::f seems to be the only
consumer of val, thus does not need to be protected. But you need to
ensure the thread runs before you call C::f. Use a condition for this
(conditions are available with pthreads and with boost thread library):

I assume RAII controled mutex, lock and condition objects and class
interface like Boost.

Mutex mutex; //shared mutex object
Condition threadFinished; //shared condition

int main() {
    int val(0);
    C aC(&val);
    { //local scope
        Lock lock(mutex); //lock mutex
        thread(&val);
        threadFinished.wait(lock); //wait for finish
    } //unlock mutex
    aC.f();
}

void thread(int* const val)
{
    *val = 1234;

    Lock lock(mutex); //lock mutex for synchronization
    threadFinished.notify_all();
}

void C::f()
{
    //do something useful
    std::cout << *val;
}

HTH,
Frank

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