I ended up calling isStdoutReady() (below) before printf() and so far it appears to work. I have tested it with slow/intermittent upload connectivity to remote terminals and also manually by holding the scroll bar on Putty windows for 40+ sec to simulate a connectivity dropout.

Pros

• takes advantage of Linux printf() buffering and handling of multiple threads
• by adding some stats, can later notify users if their console logs may be incomplete (and they should consult the event log file), and also report instances (time periods) when connectivity was lost

Cons

• discards output that can't be printed
• has to be called before every printf(). I haven't profiled the performance cost of this yet
• the timeout param is 1 msec. Zero infrequently causes a false-positive; i.e. stdout initially comes back not ready, possibly due to context switching time, so some empirical number of retries are required

@Kaz and @LuisColorado if you can edit your answers and combine with a poll() method like this or similar, I can accept and delete this answer.

int isStdoutReady() {

struct pollfd pfd;
int ret_val;

   pfd.fd = STDOUT_FILENO;
   pfd.events = POLLOUT;
   pfd.revents = 0;

   if ((ret_val = poll(&pfd, 1, 1)) > 0) {  /* timeout (in msec) is 3rd param; if set to zero will return immediately */

      if (!(pfd.revents & POLLOUT)) return 0;  /* if POLLOUT not set then stdout not ready for writing */

      if (pfd.revents & (POLLERR | POLLHUP | POLLNVAL)) return -1;  /* handle errors or hang-ups */
   }
   else if (ret_val < 0) return -1;  /* error value:  EINVAL, EAGAIN, EINTR */
   else return 0;  /* poll() return value zero is a time-out */

   return 1;  /* stdout ready for writing */
}