Make Coro threads on multiple cores with specially supported modules
Description
While Coro threads (unlike ithreads) provide real threads similar to
pthreads, python threads and so on, they do not run in parallel to each
other even on machines with multiple CPUs or multiple CPU cores.
This module lifts this restriction under two very specific but useful
conditions: firstly, the coro thread executes in XS code and does not
touch any perl data structures, and secondly, the XS code is specially
prepared to allow this.
