Asio is a cross-platform C++ library, see https://think-async.com. It provides a consistent asynchronous model using a modern C++ approach.
Please refer to the original asio documentation at https://think-async.com/Asio/Documentation. Asio also comes with a number of examples which could be find under Documentation/Examples on that web site.
ESP platform port currently supports only network asynchronous socket operations; does not support serial port and ssl. Internal asio settings for ESP include - EXCEPTIONS: Supported, choice in menuconfig - SIGNAL, SIGACTION: Not supported - EPOLL, EVENTFD: Not supported - TYPEID: Disabled by default, but supported in toolchain and asio (provided stdlib recompiled with -frtti)
ESP examples are based on standard asio examples examples/protocols/asio: - udp_echo_server - tcp_echo_server - chat_client - chat_server Please refer to the specific example README.md for details