rand() is racy in multi-threaded programs?

[Andriy Gapon]

On 03/12/2020 01:20, Conrad Meyer wrote:
> Hi Andriy,
> 
> Rand(3) is explicitly unsafe to use from concurrent threads without some
> external serialization, even after initialization. I’d suggest using a different
> API.

Conrad,

thank you!
Just want to check, unsafe in terms of bogus results (with respect to
randomness) or unsafe as in may crash?


> On Wed, Dec 2, 2020 at 13:53 Andriy Gapon <avg at freebsd.org
> <mailto:avg at freebsd.org>> wrote:
> 
> 
>     Specifically, concurrent "first" calls to rand().
>     There can be a moment when rand3_state is allocated but not completely set up
>     with initstate_r().
>     Is this a known / documented issue?
>     Should we try to do better?
> 
>     P.S.
>     I am seeing this issue from time to time when running ztest program (from ZFS).
>     I guess that it uses rand() just because that's what OpenZFS did / does on
>     illumos and Linux.
> 
>     P.P.S.
>     Just realized that the problem can be relatively recent.
>     https://svnweb.freebsd.org/base?view=revision&revision=357382
> 
>     -- 
>     Andriy Gapon
> 


-- 
Andriy Gapon