iosengineer/QueuesAndCoreDataDemo — pull request #1 by azzoor (2014-08-19 11:56:18+00:00)
Title: Update QCDCoreData.m

When you do lazy instantiation, you must make sure the "first time" through only one thread of execution will pass at the same time. You can use the following code to synchronize access to it on the main thread.