How to switch thread stack between threads?

[Alexander Tormasov]

>> 
>> So, to fix it I need during switch of context to non-local thread (setcontext() or even longjump() functions) I should update these data to current running stack.
> user level switching is only valid within the same thread. The only way to do this is to do a local
> user level switch to a user level thread that immediately blocks the os level thread and wakes the os level
> thread, that is blocked in the same procedure and corresponds to the target user level thread. At wakeup that
> user level thread, which was blocked at the os level, reads the target user level thread and makes a local
> user level switch to it.
> The Mutex on which the user level threads blocks (at least its address) needs to be part of the context.

probably I give a wrong picture of operations
1. I run arbitrary function with stack associated with first thread
2. I copy current context using getcontext and store it somewhere
3. I stop doing function from 1, by switching to another function/stack associated with thread 1
4. after some time I create a new os thread and run some code inside it
5. then inside 2 thread I take old context from 2 above and perform setcontext from inside 2 thread to replace current function with state in the thread to the first one

So, I don’t need mutexes and wait for something - I have a time gap between suspend of function in os 1 and it continuation on thread 2.
during continuation I already switched to thread 2… 
just need to associate old stack with it (it contains state of function/stack from 1)