shutdown on a socket is similar to close on a pipe in
what information it gives to the program on the other side.
But it does not close the file handle.
shutdown(0) is like close on a pipe that you are reading
from -- it tells the other side that you will no longer be
reading (which will change how select behaves, for
example). shutdown(1) is like close on a pipe that you
are writing to -- it sends an end-of-file to the reader on
the other side. shutdown(2) says both of these things, but
doesn't close the handle.
The reason for shutdown(0) and shutdown(1) is easy to see
because a socket is two-way and you couldn't use close to
send an end-of-file but still continue to read from the
"perldoc -f shutdown" says that shutdown is "a more
insistent form of close because it also disables the
file descriptor in any forked copies in other processes".
It is saying that just closeing the socket doesn't
prevent any forked processes that also have the same
socket open from deciding to read or write data. But it
doesn't free any file handles or file descriptors, in any
process, including the current one.
So the basic answer is to close after you shutdown.
I had always assumed that the last close on a socket
also did a shutdown(2). However, it now appears that
some TCP/IP stacks don't do this (I consider this a bug
and I'm rather surprised by it, but it is the simplest
explanation I've found for the very high number of incoming
web connections that we see that must time out because
they never appear to close). So, a good network
citizen will shutdown(2) before they close (if the
close is meant to end communication rather than just
turn communication responsibilities over the some other
(but my friends call me "Tye")
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