Re: clone hang prevention / timeout?

From: Eric Wong <normalperson@yhbt.net>
Date: Apr 12, 2016, 08:01 UTC
Message-ID: <20160412080149.GA9087@dcvr.yhbt.net>
In-Reply-To: <CALyZvKwxE4T8-FmEYgPMgAFKLmeAY5f-y-mDL8S9twTb0umRaA@mail.gmail.com>

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.

Show 7 quoted lines

> 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")