I know Singleton pattern has been discussed so much. But because I'm not fully understand the memory management mechanism in Objective-C, so when I combined Singleton implementation with multithreading, I got a big error and cost me a whole day to resolve it.

I had a singleton object, let's call it ObjectX. I declared an object inside ObjectX that will detach a new thread, let's call that object objectWillSpawnNewThread, when I called

[[ObjectX sharedInstance].objectWillSpawnNewThread startNewThread];

The new thread could not be executed correctly, and finally I found out that I should not declare the object objectWillSpawnNewThread inside the singleton class.

Here are my questions:

1. How does Objective-C allocate static object in the memory? Where does Objective-C allocate them(Main thread stack or somewhere else)?
2. Why would it be failed if we spawn a new thread inside the singleton object?

I had searched the Objective-C language [ObjC.pdf] and Objective-C memory management document, maybe I missed something, but I currently I could not find any helpful information.