concurrent async_write on the same strand
Here is an example: https://www.boost.org/doc/libs/1_74_0/libs/beast/example/websocket/server/chat-multi/websocket_session.cpp
locking shared objects in a multi-threaded environment
The documentation here: https://1973.beastdocs.prtest.cppalliance.org/libs/beast/doc/html/beast/ref/boost__beast__websocket__stream.html