i updated my mac book to mountain lion and Xcode to the 4.4 version. In the pre version I had no problems with closing the iOS simulator and Xcode stopped automatically the building process but now if I close the iOS simulator the build process in Xcode is still running and I have to force quit Xcode because it freezes.
Does anyone recognize this bug, or can you help me to solve this problem?
As a workaround, I've noticed that Running (⌘ + R) and then Bulding (⌘ + B) product succesfully starts new simulator instance, although the old instances are still frozen.
I just reverted to doing something I used to do when this started happening to me back in XCode 3.1 or something.
Press the STOP button in XCODE before you close or background the app in iOS SIMULATOR.
Then close the iOS SIMULATOR.
来源：https://stackoverflow.com/questions/11691035/xcode-4-4-ios-5-1-simulator-problems