snmp_select_info() timeout behaviour

Greetings,

I've been writing a subagent against net-snmp 5.7.1 under a 64-bit
ubuntu linux install, based on the example subagent code
(http://www.net-snmp.org/tutorial/tutorial-5/toolkit/demon/example-demon.c),
using the snmp_select_info() API. In addition to handling snmp
communication with the master, it is sending messages to a nox
application on a regular interval, and dealing with responses from
that socket.

It seems that if select() times out after <15secs, then I call
snmp_select_info(), it will try to set the timeout so that it will
expire 15sec after the original call. All subsequent calls to
snmp_select_info() set the timeout to 1usec.

Example: if poll_interval_ = 14sec,
- socket() times out after 14s, and a message is sent. I reset the
timer to 14sec.
- when snmp_select_info() is next passed the timer object, it resets
the timer to ~1sec.
- After this timeout, I reset the timer to 14sec, then
snmp_select_info() changes the timeout to {0,1}.
- Repeat the last step ad infinitum!

Why does net-snmp do this? It seems to be fine if I set poll_interval_ >=15sec.

Am I missing some API calls that I should be making?

Below is the main loop of the code I'm using, followed by the output I
see. The code beforehand is mostly the same as the example, with a
couple of extra variable declarations, socket setup, sending an
initial msg to noxfd.

-- CODE --
  /* Set up our timers */
  struct timeval expire_time,timer;
  timerclear(&timer);
  timerclear(&expire_time);
  timer.tv_sec = poll_interval_;

  size_t len = 0;
  while(keep_running_) {
    FD_ZERO(&fdset);
    FD_SET(noxfd, &fdset);

    fprintf(stderr, "Timer check %d:%d\n", timer.tv_sec, timer.tv_usec);

    gettimeofday(&expire_time, NULL);
    expire_time.tv_sec += poll_interval_;

    snmp_select_info(&numfds, &fdset, &timer, &block);

    fprintf(stderr, "Timer check1 %d:%d\n", timer.tv_sec, timer.tv_usec);

    count = select(numfds, &fdset, NULL, NULL, &timer);

    if (count == 0) {
      /* Regular stats request sending */
      if (send(noxfd,stats_msg, strlen(stats_msg), 0) != 0)
        snmp_log(LOG_ERR, "Failed to send stats_request");

      snmp_timeout();
      timer.tv_sec = poll_interval_;
      timer.tv_usec = 0;
      fprintf(stderr, "Timer reset %d:%d\n", timer.tv_sec, timer.tv_usec);
    } else if (count > 0) {
      /* Either nox or netsnmp has an event to deal with */
      if(FD_ISSET(noxfd, &fdset)) {
        if ((len = read(noxfd, buf, 2048)) > 0) {
          parse_response(buf, len);
        }

        /* Make sure snmp_read() doesn't tinker with our noxfd */
        FD_CLR(noxfd, &fdset);
        --count;
      }
      if (count > 0) /* If there are SNMP events */
        snmp_read(&fdset);

      struct timeval current;
      gettimeofday(&current, NULL);
      timersub(&expire_time, &current, &timer);

      fprintf(stderr, "Timer check2: %d:%d\n", timer.tv_sec, timer.tv_usec);
    }
  }

-- OUTPUT --
Timer check 14:0
Timer check1 14:0
Parsing response...
Timer check2: 13:998949
Timer check 13:998949
Timer check1 13:998949
Timer reset 14:0
Timer check 14:0
Timer check1 0:985627
Timer reset 14:0
Timer check 14:0
Timer check1 0:1
Timer reset 14:0
Timer check 14:0
Timer check1 0:1
Timer reset 14:0
Timer check 14:0
Timer check1 0:1
Timer reset 14:0
Timer check 14:0
...

Any help would be appreciated.

Cheers,
Joe

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