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

[Jonathan Larmour]

Clive Wilson wrote:
> At 10:20 31/05/2007, you 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.

Jifl
--
eCosCentric Limited      http://www.eCosCentric.com/     The eCos experts
Barnwell House, Barnwell Drive, Cambridge, UK.       Tel: +44 1223 245571
Registered in England and Wales: Reg No 4422071.
------["The best things in life aren't things."]------      Opinions==mine