What does autoflush do in socket? why do we use it?
I am working on some socket code and unable to figure out why there is autoflush used on socket. It is something like this
my $sock = IO::Socket::Unix(Peer => $socketfilename , Type => SOCK_STREAM)
autoflush $sock 1;
Also there are places with
autoflush STDERR 1
autoflush STDOUT 1
for general filehnadles.
What does it do? Also what happens or will happen if I don't use it? Please give some practical example so that I will understand rather than simple definition.
Answer
Data doesn't usually get sent right away on the socket, it is buffered up to a certain point and then sent all-at-once.
Auto-flushing means data goes right through the buffer and then flushed out, not kept in the buffer waiting for other data to arrive and accumulate.
As simple as that.
Without auto-flush:
Tick | DATA sent|Socket Buffer| DATA received
.....|..........|.............|..............
1 | XX | XX | (nothing)
2 | yy | yyXX | (nothing)
3 | ZZZ | ZZZyyXX | (nothing)
4 | t | (empty) | tZZZyyXX
With auto-flush:
Tick | DATA sent | Socket Buffer | DATA received
.....|...........|...............|..............
1 | XX | () | XX
2 | yy | () | yy
3 | ZZZ | () | ZZZ
4 | t | () | t
- Socket Buffer size: 8 chars
- Very simple example, you might raise some other questions after seeing it - a big part of it is also implementation-dependent. Moreover, buffering can happen at various levels (sender, receiver, application, etc.. )