!7

static int serveLongPoll_checkInterval = 100;

// f: func -> O (null or empty string if no result yet)
static O serveLongPoll(long timeout, int interval, O f) {
  long startTime = sysNow();
  while (sysNow() < startTime+timeout) {
    O o = callF(f);
    if (nempty(o)) ret o;
    sleep(serveLongPoll_checkInterval);
  }
  ret "";
}

static O serveLongPoll(long timeout, O f) {
  ret serveLongPoll(timeout, serveLongPoll_checkInterval, f);
}

Began life as a copy of #1014866