Re: clone hang prevention / timeout?

[Eric Wong <normalperson@yhbt.net>]

Jason Vas Dias <jason.vas.dias@gmail.com> wrote:
> It appears GIT has no way of specifying a timeout for a clone operation -
> if the server decides not to complete a get request, the clone can
> hang forever -
> is this correct ?

git uses SO_KEEPALIVE for all connections it makes, so whatever
your kernel TCP keepalive knobs are set at.

By default, it's very long (around 2 hours), but you can change them
using the tcp_keepalive_* knobs in /proc/sys/net/ipv4/ under Linux.

I suppose we can do shorter timeouts (at least under Linux) via
setsockopt(.. TCP_KEEP*) knobs, or we can call poll() ourselves
to timeout connections.  However, git packing operations on the
server can take a long time; so it might be bad to timeout
manually unless we know the connection is really dead.

> This appears to be what I am seeing, in a script that is attempting to do many
> successive clone operations, eg. of
> git://anongit.freedesktop.org/xorg/* , the script
> occasionally hangs in a clone - I can see with netstat + strace that the TCP
> connection is open and GIT is trying to read .
> Is there any option I can specify to get the clone to timeout, or do I manually
> have to strace the git process and send it a signal after a hang is detected?

I added git:// support for SO_KEEPALIVE in commit e47a8583a202
("enable SO_KEEPALIVE for connected TCP sockets")
back in 2011 (v1.7.10),
and http:// support later in 2013 (v1.8.5) with
commit a15d069a1986 ("http: enable keepalive on TCP sockets")