[zeromq-dev] Fwd: assertion at mailbox.cpp:182

Pavel Gushcha pavimus at gmail.com
Mon Jan 31 16:57:24 CET 2011

> > I'm not very involved into zmq2 internals, but as i understood, socket
> > buffer must have bigger size, that message_t class. And message_t has
> > relatively small size than my net.core.wmem_default = 126976. May be
> > zmq::mailbox_t::send tries to increase socket buffer in case when it
> > have big size but is full too?
> >

> We don't have api plumbing to change mailbox socket buffer sizes yet,
> ie. ZMQ_SNDBUF and ZMQ_RCVBUF don't apply.
> You'd have to change them manually, can you try changing wmem_default
> and rmem_default?
> Note wmem_default and rmem_default are capped by wmem_max and
> rmem_max, so you'd have to change them too.

Thanks you for reply, Dhammika!
which value you suggest try to set for wmem_default and rmem_default,
the default value 124kb is not enough?
For me is not 100% unclear, in which case zmq try to increase buffer by:

   //  Attempt to increase mailbox SNDBUF if the send failed.
   if (nbytes == -1 && errno == EAGAIN) {
       int old_sndbuf, new_sndbuf;
       socklen_t sndbuf_size = sizeof old_sndbuf;

       //  Retrieve current send buffer size.
       int rc = getsockopt (w, SOL_SOCKET, SO_SNDBUF, &old_sndbuf,
       errno_assert (rc == 0);
       new_sndbuf = old_sndbuf * 2;

       //  Double the new send buffer size.
       rc = setsockopt (w, SOL_SOCKET, SO_SNDBUF, &new_sndbuf, sndbuf_size);
       errno_assert (rc == 0);

       //  Verify that the OS actually honored the request.
       rc = getsockopt (w, SOL_SOCKET, SO_SNDBUF, &new_sndbuf, &sndbuf_size);
       errno_assert (rc == 0);
       zmq_assert (new_sndbuf > old_sndbuf);

       //  Retry the sending operation; at this point it must succeed.
       do {
           nbytes = ::send (w, &cmd_, sizeof (command_t), 0);
       } while (nbytes == -1 && errno == EINTR);

I can only suppose, that this code try to increase buffer each time,
when it has no free space to send message_t. When this is correct,
theoretically in busy system buffer size may grow without limits.
Problem is very hard to reproduce. now my app have 1 day uptime...

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