Good user-space threading libraries for C++?

Question

linux

The task is to write serious network software that requires support for a large number of simultaneous requests. There is an idea to simplify development / debugging / support by replacing the use of the asynchronous boost:: asio API with work with preemptive threads in user-space. So that they can be produced in millions, as in Erlang.
Can you suggest a good library for such multithreading with support for a wide range of system calls (linux)? Erlang not to offer.
Thank you.

Answer 1

Boost Coroutine? It seems that asio is friends with him.

Answer 2

If compilers support C++11, then it is possible without third-party libraries.

Answer 3

I don't think preemptive multitasking in userspace is possible in native code. If you have launched some code for execution, then you will not be able to control it from userspace.
In the same erlang there is a virtual machine that controls the execution.
You can also try golang if you don't like erlang. Although there, it seems, too, light threads are built on the basis of coroutines