Hi

The use case here is for C-based statistical profilers. When running vmprof on linux/os x, you can get the current thread state from PyThreadState_GetUnchecked or a similar solution. However, on windows you need to walk all the interpreter state, for which there is an API. However that API is only ever used with locks (HEAD_LOCK/HEAD_UNLOCK), which are not exposed, which turns API mostly useless.