[boost] Re: Smart Pointers - (many) thanks and (some) questions

From: David Abrahams (root) (abrahams_at_[hidden])
Date: 1999-12-28 08:48:27

scleary_at_[hidden] wrote:
> 
> Giora Unger wrote:
> 
> > 1. As far as I understand, the library is NOT thread safe.
> >    Am I wrong ?
> >    For example, let's examine line 169 in smart_ptr.h:
> >       if (--*pn == 0) { delete px; }
> >    I believe, that in case of two threads concurrently accessing
> >    this line (the reset() method), and an initial reference count==2,
> >    then a crash is possible: if both decrements occur before both
> >    comparisons, resulting in two deletion attempts.
> 
> The smart pointers are just as thread-safe as integers. 

I don't think that's entirely correct. On many platforms, all integer
operations are atomic; the same can't be said of our smart pointers.

> To use them in a
> thread-safe way, protect them just as you would any other non-thread-safe
> fundamental type/class/library.

Good advice.

> Should we look at doing a portable multi-threading library?  I have the
> beginnings of one, but it doesn't allow timed waits or waiting for multiple
> objects -- would these be considered essential or optional?
 
Oh, optional, optional (though highly desired)!
Portable multi-threading is badly needed!

-Dave