[lwip-devel] [bug #20021] conn->sem is only signaled one-way

[Jonathan Larmour]

Follow-up Comment #6, bug #20021 (project lwip):

Just to clarify something from the original submission that I mentioned on
the mailing list, the semaphore is not waited on only once. It is waited also
in this part of netconn_write:
      while ((sndbuf = tcp_sndbuf(conn->pcb.tcp)) == 0) {
        sys_sem_wait(conn->sem);
        if (conn->err != ERR_OK) {
          goto ret;
        }

>From what I can see the code here (and in sent_tcp) is treating the semaphore
as a binary semaphore not a counting semaphore.

I think there would be race conditions with the suggested solution of
something that tries to indicate that someone's waiting.

I think it would be easiest to set down that lwIP expects binary semaphores
only. 

Alternatively, you can move the current send buffer test into the tcp/ip
thread (so the caller thread effectively always waits, and its up to the
tcpip thread to whether it resumes). We had already talked about this in
fact, because the call to tcp_sndbuf is a race condition already.



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