I expanded the implementation of the class strand of the Networking
TS. Essentially, I
implemented a token system so each thread knows when it can execute;
the system is organized
with 2 integers moving as a clock.

2021-03-12 Alessio G. Baroni <alessiogiovanni.baroni@gmail.com>

        libstdc++-v3:
            * include/experimental/executor: Implemented algorithm for
serial execution regardless of the underlying Executor.