title: mach_msg_trap in core-data
body: <p>What is meant by mach_msg_trap error?
  I'm developing an application with core-data. I get this error when ManagedObjectContext if a different thread is "used" the second time.
  I've a producer consumer kind of threading system. The producer thread and the consumer thread uses the same underlying sqlite db, but different managedobjectContext as they are on different threads.
  But I want the producer thead to check new data and if any, i want it to update my managedObjectContext. But the second time it runs the app crashes giving the above result.</p>
  
  <p>Please help...</p>