Re: [lwip-users] SemSignal gets called on a already signaled semaphore

[clive]

address@hidden wrote:
> Goldschmidt Simon wrote:
> >>>>So waiting on a semaphore would mean:
> >>>>lock mutex
> >>>>while (count==0)
> >>>>  wait on condition variable
> >>>>count--
> >>>>unlock mutex
> >>>>
> >>>>And posting a semaphore:
> >>>>lock mutex
> >>>>count++
> >>>>signal condition variable
> >>>>unlock mutex
> >>>
> >>>
> >>>Jonathan,
> >>>
> >>>As a clarification of the above example, is the intention for the 
> >>>mutex used by the semaphore pend to be the same as the one 
> >>
> >>used by the 
> >>
> >>>semaphore post? I imagine not, otherwise the pend would wait on the 
> >>>condition variable with the mutex locked, therefore 
> >>
> >>preventing a post 
> >>
> >>>from occurring...
> >>
> >>It is the same mutex. Condition variables always have a mutex 
> >>associated with them. When you wait on a CV, the mutex is 
> >>automatically unlocked by the OS, and when you wake up after 
> >>the CV is signalled, the OS automatically relocks the mutex 
> >>before the wait function returns.
> >>
> > 
> > 
> > Reading that explanation I'm afraid the OSes I use don't have such
> > condition variables! So making them mandatory for lwIP seems not
> > such a portable idea to me...
> 
> Really? I'm amazed if so. Any OSes I should have heard of, or homegrown? I 
> am sort of assuming that if someone can write a homegrown OS they can 
> implement mutexes/condition variables for it if they need to.

Well, that's the reason for my needing a clarification. The OS I'm using (VDK, 
Analog Devices' RTOS for their DSPs) has no such condition variable, and I 
don't think it's unique in that regard either.

Kind regards,

Clive Wilson