global_i doesn't exist, see comment assert(global_i == 0); // Oops!

[blockspacer]

global_i not declared

What assert(global_i == 0); // Oops! means?

See https://github.com/apolukhin/Boost-Cookbook/blob/912e36f38b9b1da93b03ae7afd19fcec0900aa83/Chapter05/02_mutex/main.cpp#L40

[apolukhin]

Thanks for the report! It should be shared_i

Fixed in the sources