Re: [Boost-users] [smart_ptr] weak_ptr pointer semantics

Subject: Re: [Boost-users] [smart_ptr] weak_ptr pointer semantics
From: Peter Dimov (pdimov_at_[hidden])
Date: 2011-11-11 15:14:02

Szymon Gatner wrote:

> On the second thought on weak_ptr's rationale with regards of 
> thread-safety, what about this:
>
> if (!weak.expired())
> {
>   // here it can expire from other thread
>   weak.lock()->thisWillCauseAssert();
> }
>
> Isn't this how weak_ptr<> is suppose to be used?

No, it isn't.

if( shared_ptr<> p = weak.lock() )
{
    p->thisWillNotAssert();
}

expired() should only be used for positive tests: if( weak.expired() ). Once 
a weak_ptr expires, it stays expired, so there is no potential for a race.