Cancelation points in async

[QMaster]

In my example there's a 1 second pause, but it might be 15 minutes easily. What 
socket should I close to stop it from waiting those next 15 minutes? I can't 
close the socket of the connection before I've done everything to gracefully 
shutdown it and cancelling all the sending and waiting tasks and signalling to 
the waiters. I will reask the question from "Data loss with async sockets" 
thread: Is it possible to port the cancellation code and cancellation points 
from chronos library?