Re: [Boost-users] weak_ptr and thread safety

Subject: Re: [Boost-users] weak_ptr and thread safety
From: Peter Dimov (pdimov_at_[hidden])
Date: 2009-07-22 15:27:25

Pavel Shevaev wrote:
> Guys, could you please clarify whether the following usage of weak_ptr
> is thread safe:
> 
> //thread A:
> shared_ptr<Foo> p = wp.lock();
> 
> //thread B:
> p.reset();

p is local to thread A, so B can't reset it.

    // thread B:
    wp.reset();

is not safe (A reads wp, B writes wp).

    // before A and B
    shared_ptr<X> p( new X );
    weak_ptr<X> wp( p );

    // A
    shared_ptr<X> p2 = wp.lock();

    // B
    p.reset();

is safe (A reads wp, B writes p).