Re: [RFC 1/2] sem-posix: remove the posix semaphore support

[Paolo Bonzini]

On 2/21/22 12:11, Daniel P. Berrangé wrote:
> As a point of history, the original  code only used sem_t. The pthreads
> based fallback was introduced by Paolo in
>
>    commit c166cb72f1676855816340666c3b618beef4b976
>    Author: Paolo Bonzini <pbonzini@redhat.com>
>    Date:   Fri Nov 2 15:43:21 2012 +0100
>
>      semaphore: implement fallback counting semaphores with mutex+condvar
>      
>      OpenBSD and Darwin do not have sem_timedwait.  Implement a fallback
>      for them.
>      
>      Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>      Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>
> I'm going to assume this fallback impl is less efficient than the
> native sem_t impl as the reason for leaving the original impl, or
> maybe Paolo just want to risk accidental bugs by removing the
> existing usage ?

Yes, it is a bit less efficient.  But really there aren't any places 
where semaphores vs. mutex+condvar will make a difference.  The original 
reason to use semaphores was that Windows had a hand-written condition 
variable implementation that didn't support cond_timedwait.

Paolo