Close server connections and shutdown coroutines immediately on disconnect

[Al2Klimov]

No description provided.

[Al2Klimov]

Theoretically ready, but I'd like to

• wait for feedback in Icinga2 doesn't close connections #7203 first.

[dnsmichi]

Hmmm if I overload the API with many requests, and then run into too many open files, the sockets will stay in CLOSE_WAIT - but only after it heals itself with closing requests then.

This PR

A typical test case with 100 parallel connections and 5 curl requests works just fine.

michi@mbpmif ~ $ pidof icinga2
13115 13129
michi@mbpmif ~ $ watch -n 1 -c 'lsof -p 13115 | grep TCP | wc -l && lsof -p 13115 | grep TCP'

for i in {1..100}; do sh -c "curl -k -s -u root:icinga 'https://localhost:5665/v1/objects/services?[1-5]' >/dev/null &"; done

At first, this starts with 100+1.

Then it jumps over to ~200 with sockets in close_wait and the next curl request.

After a while all requests are finished and the only socket remaining is the listening socket.

[dnsmichi]

2.10.2 doesn't leak either. The accepts there are faster, pushing the thread pool and my macbook to the limits. So it is good that we take care of this, preventing strange customer problems.