Re: git diff looping?

From: Jeff King <peff@peff.net>
Date: Jun 16, 2009, 11:47 UTC
Message-ID: <20090616114726.GA4343@coredump.intra.peff.net>
In-Reply-To: <3ae83b000906151837r186221f2q1f8a670f13841877@mail.gmail.com>

On Mon, Jun 15, 2009 at 06:37:21PM -0700, John Bito wrote:

> Running Git 1.6.1 on Solaris 10, git diff seems to go into a loop -
> consuming CPU and producing no output after a little bit.  While the
> repository isn't small, it's not huge (it's
> http://repo.or.cz/w/egit.git). I've tried the following:

I can reproduce the problem on Solaris 8 using git v1.6.3. It seems to be caused by a horribly slow system regex implementation; it really chokes on the regex we use to find the "funcname" line for java files. I tried running "git diff v0.4.0" and it still hadn't finished after 90 seconds. Then I did:

  git config diff.java.xfuncname foo ;# some garbage regex
  git diff v0.4.0

and it completed in about 2.5 seconds.

Can you try that and see if it works around the problem for you?

If anybody wants to look further into the problem, I think it is specifically triggered by this file (and the built-in xfuncname for java files):

  $ git clone git://repo.or.cz/egit.git
  $ git diff v0.4.0 -- \
    org.spearce.egit.core.test/src/org/spearce/egit/core/op/T0001_ConnectProviderOperationTest.java

which isn't even all that big a file, but it is either causing some horrible algorithmic behavior in the regex library, or is outright sending it into an infinite loop.

I tried building against the code in compat/regex; it completes in a reasonable amount of time, though it is still noticeably slow. With system regex, the diff given above doesn't complete in less than 90 seconds (at which I get bored and kill it). With compat/regex, it completes in about 2.2 seconds. Disabling the xfuncname, it completes in 0.14 seconds.

So I think it is a viable solution to recommend building against compat/regex on Solaris, but I think there is still room for improvement in what we ship in compat/.

-Peff