title: How to find out what mach_msg_trap waits for?
body: <p>I a profiling my iPhone application on target, and according to Instruments 65% of the time is spent in <code>mach_msg_trap</code>.</p>
  
  <p>I have a background thread that runs-forever and send results back to the main thread using <code>performSelectorOnMainThread:withObject:waitUntilDone:</code>, aproximately every 2 seconds. I am not waiting until done.</p>