postevent is clearly thread safe, as it is often used for thread safe communication, and OpenGL's MakeCurrentContext is threadsafe as well, as all OpenGL Context's are held in TLS. This is how you do shared resources between multiple contexts
Merge pull request #105 from dannydulai/2884f2f5671b094b919648b1aaa624768dc3c810

Thread safe apis (nsapplication's postevent and opengl's makecurrentcontext)