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

Frank Birbacher <>
Thu, 28 May 2009 13:49:28 CST

vl106 schrieb:

int main() {
    int* val = new int(0);
    C aC(val);
    return 0;

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

int main() {
    int val(0);
    C aC(&val);

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
        threadFinished.wait(lock); //wait for finish
    } //unlock mutex

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

    Lock lock(mutex); //lock mutex for synchronization

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


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