ldm/src/main/thredds/ldm/MessageWriter.java
void scheduleWrite(Message m) {
    q.add(m);
    if (!isScheduled.getAndSet(true)) {
      executor.submit( this);
    }
  }
void scheduleWrite(Message m) {
    q.add(m);
    if (!isScheduled.getAndSet(true)) {
      executor.submit( this);
    }
  }
put a message on the queue, schedule writing if not already scheduled.