[PD-dev] about [tcpserver] (mrpeach and iemnet)

[Roman Haefeli]

Hi Martin, IOhannes et al.

Martin, you asked me when I last tested mrpeach's [tcpserver] when I was
mentioning the blocking issue. I did another test today with two
computers connected over Ethernet. When plugging out the chord, I can
simulate a client disappearing without the server noticing and thus
filling the socket buffer on the server side. 
The behavior of [tcpserver] indeed changed since last time I tried. The
test setup consisted of a server and a client on Computer A and a client
on computer B. Client A sent messages that were broadcasted to both
clients by the server. When plugging out the cable, client A (which is
running on the same box as the server) did first still receive the
messages. After a while, the server started printing lots of errors:

error: tcpserver_broadcast: couldn't create broadcast thread (11)

>From then also client A didn't receive any messages anymore, although
the client was still sending messages to the server. After I plugged
client B back in, it received all the messages sent by client A from the
moment I unplugged the cable until the server started printing errors.
However, all the subsequent messages (the ones, that triggered the
errors) got lost.

The advantage of this behaviour is that the clients don't get blocked
because the server is  blocked. But this also means, that when the
server is blocked, data is lost. Really problematic is the fact, that
from the patch there is no way to detect such a data loss (or is
there?). The old implementation (used still by [maxlib/netserver] and
also [netsend]) blocks, but never loses any data. Though I think the new
non-blocking behaviour is good, there should be a mechanism to know what
got lost, so that a patch can handle such a situation and make sure to
resend the data.

iemnet's [tcpserver] is again different, in that it buffers huge amounts
of data without ever blocking. In my tests I wasn't able neither to
block a client nor the server, nor to lose any data. Even if I let the
client A sent a ton of data while client B was unplugged, after plugging
client B back in, it received all the data that was sent in the
meanwhile without dropping one single message. 

@ IOhannes
Though I like this 'stable'/reliable behaviour of iemnet's [tcpserver],
I wonder what happens, if it keeps sending data to the unreachable
client. Will it just go on and buffer everything until the whole RAM of
the computer is consumed? If so, wouldn't it be more wise to just
disconnect that client at some point in order to avoid the box running
out of memory?

Roman