Pavel Vasiliev wrote:
>
> Alexander Terekhov wrote:
>
> [...]
> >> Pavel Vasiliev wrote:
> >> > The true locking/unlocking, not InterlockedIncrement/Decrement()
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> > Nah, pthread_refcount_t. ;-)
>
> >> > even if availabe, is necessary to support weak references.
> >> > [...]
> >>
>
> > It's probably a bit more exciting to take care of all possible races
> > without "a true lock" protecting both counters. I'm not sure that the
> > true locking is *necessary* to support weak references. Do you have
> > an illustration, Pavel?
>
> May be the following code answers the challenge? :-). ...
Not bad. ;-) Well,
//*** ES and error checking aside...
class refs {
public:
refs() {
pthread_refcount_init(&strong_count, 1);
pthread_refcount_init(&weak_count, 1);
}
~refs() {
pthread_refcount_destroy(&weak_count);
pthread_refcount_destroy(&strong_count);
}
//*** Called by existing "strong_ptr".
void acquire_strong() {
pthread_refcount_increment(&strong_count);
}
void release_strong() {
int status = pthread_refcount_decrement(&strong_count);
if (PTHREAD_REFCOUNT_DROPPED_TO_ZERO == status) {
destruct_object();
release_weak();
}
}
void acquire_weak_from_strong() {
acquire_weak();
}
//*** Called by existing "weak_ref".
void acquire_weak() {
pthread_refcount_increment( &weak_count );
}
void release_weak() {
int status = pthread_refcount_decrement_no_msync(&weak_count);
if (PTHREAD_REFCOUNT_DROPPED_TO_ZERO == status)
destruct_self();
}
bool acquire_strong_from_weak() {
int status = pthread_refcount_enroll_one(&strong_count); // _many( &refcount, 1);
if (PTHREAD_REFCOUNT_DROPPED_TO_ZERO == status) // Ouch, did not work [too late].
return false;
return true;
}
private:
void destruct_object(); // "delete p_object".
void destruct_self(); // "delete this".
pthread_refcount_t strong_count;
pthread_refcount_t weak_count;
T* p_object;
}; //*** class refs
Or am I just missing and/or misunderstanding something?
regards,
alexander.
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