Re: [Boost-users] shared_ptr and weak_ptr concurrency

Subject: Re: [Boost-users] shared_ptr and weak_ptr concurrency
From: Stefan Strasser (strasser_at_[hidden])
Date: 2009-09-04 16:25:40

Am Friday 04 September 2009 20:42:48 schrieb John Dlugosz:
> I agree that "just like built-in types" would not hold for the nonstandard
> implementation behavior of atomic reads and writes, so many people might
> misunderstand that.
>
> I've had to implement smart-pointer like things that do have this feature,
> so it must be carefully designed to have only a single pointer in the main
> struct and update things to maintain a valid state at all times (e.g. swap
> in that main pointer last).  I don't suppose a standard-conforming
> shared_ptr would have that feature unless explicitly advertised as such.

can you point to anything that the boost shared_ptr does that is unsafe in the 
one-writer-multiple-reader case?
TR1 doesn't mention thread safety or atomicity at all, so strictly speaking 
the guarantee that the boost shared_ptr doc gives is already an extension.

writing to an expired weak_ptr while multiple readers are trying to lock() it 
seems safe to me. (in the current implementation)