synchronized void addTracer(Tracer tracer){
  if (curTracers.add(tracer)) {
    LOG.trace(toString() + ": adding tracer " + tracer.toString());
  }
}

synchronized void addTracer ( Tracer tracer ) { if ( curTracers . add ( tracer ) ) { LOG . trace ( toString ( ) + ": adding tracer " + tracer . toString ( ) ) ; } }
add a new tracer .
