Re: Antw: RE: [lwip-users] SemSignal gets called on aalreadysignaled semaphore

[Jonathan Larmour]

Goldschmidt Simon wrote:
> > I stepped a little bit around now. The semaphore causing the 
> > problem is created inside the accept_function() in api_msg.c line 242:
> >
> > newconn->sem = sys_sem_new(0);
> >
> > It is then signaled in sent_tcp() in api_msg.c line 159. But 
> > I can't find the file where this (connection specific) 
> > semaphore is ever waited on. So it gets signaled and signaled 
> > and signaled....
>
> 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.

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.

Jifl
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