signal_and_slot.md
http://quinnftw.com/c++-signals-and-slots/
https://theboostcpplibraries.com/boost.signals2
https://www.boost.org/doc/libs/1_80_0/doc/html/signals2.html
http://t.zoukankan.com/Glucklichste-p-11488746.html

https://github.com/fr00b0/nod

https://blog.csdn.net/mystyle_/article/details/107642564 std::bind class member

https://github.com/Montellese/cpp-signal
https://github.com/Montellese/cpp-signal#performance

https://github.com/NoAvailableAlias/signal-slot-benchmarks
https://github.com/palacaze/sigslot

observer pattern
publish/subscribe
https://zhuanlan.zhihu.com/p/51357583
发布订阅模式里，发布者和订阅者，不是松耦合，而是完全解耦的 broker
channel
actor