RE: Antw: RE: [lwip-users] SemSignal gets called on aalreadysignaledsemaphore

[Goldschmidt Simon]

> > That conn->sem seems only to be waited for when running out 
> of memory.
> > If you always send so little data that you never run out of 
> memory (or 
> > window size), it never gets waited for. Can any other developer say 
> > something on this? I think this behaviour is strange...
> 
> I agree. It is treating it as a binary semaphore.
> 

Yes. And the reason that problem didn't occur to me is that my
semaphores can count up to 0xFFFFFFFF since they don't have a
maximum value. And reaching that level needs kind of long ;-)

> It turns out sys_arch.txt says "Semaphores can be either 
> counting or binary
> - lwIP works with both kinds."
> 
> And my own port uses a counting semaphore. But the situation 
> that would tickle this problem would probably be infrequent 
> in practice, but certainly would appear to happen sometimes.
> 
> I've had a quick look and I can't see any dependencies 
> elsewhere on it being a counting semaphore. So perhaps the 
> answer is that we must mandate a binary semaphore after all.

I think a better solution would be to redesign tcp_sent() to signal
the semaphore only if someone is really waiting.
Otherwise some OSes could throw errors if a binary semaphore is
signaled more than once.


Simon