Re: gitk management of git diff-tree processes

[David Holmer <dholmer@persistentsystems.com>]

On Tue, 2009-09-22 at 11:10 -0400, David Holmer wrote: 
> I find that if I am in gitk browsing through commits, gitk seems to be
> spawning a git diff-tree process in order to display the changes and
> patch file list in the bottom panes.
> 
> I have a certain commit that adds a very large amount of data to my
> repository (1.2 GB). Understandably, the git diff-tree process that
> tries to display the changes in this commit takes a VERY long time to
> run (e.g. churns indefinitely).
> 
> The issue is that I find that if I simply browse past this commit (e.g.
> using up/down arrows), gitk starts up a git diff-tree process and leaves
> it running. As many times as I pass the commit (e.g. while looking at
> changes before and after this commit), I end up with multiple processes
> all running and my CPUs quickly go to 100%. Furthermore, even if I exit
> gitk, all the git diff-tree processes keep running unless I manually
> kill them.
> 
> Perhaps gitk could kill the git diff-tree process it spawns if its
> output is no longer needed (e.g. user browses to a different commit, or
> gitk exits).
> 
> Thank you,
> David
> 
> $ ps -aF
> UID        PID  PPID  C    SZ   RSS PSR STIME TTY          TIME CMD
> david    23635     1 18 88365 102892  0 10:49 pts/1    00:01:11 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23640     1 18 88368 102908  1 10:49 pts/1    00:01:10 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23644     1 16 88368 102904  0 10:49 pts/1    00:01:04 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23646     1 16 88367 102916  0 10:49 pts/1    00:01:04 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23652     1 17 88365 102892  1 10:49 pts/1    00:01:07 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23656     1 17 88368 102920  1 10:49 pts/1    00:01:06 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23660     1 16 88369 102932  0 10:49 pts/1    00:01:03 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23664     1 16 88368 102908  0 10:49 pts/1    00:01:03 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23670     1 16 88368 102904  1 10:49 pts/1    00:01:03 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23680     1 17 88365 102896  1 10:49 pts/1    00:01:05 git diff-tree -r -p --textconv -C --cc --no-commit-id -U3 8df50645c4cadf26dc951540e0c713b0826247b8
> david    23851 10444  0   692  1032   0 10:56 pts/1    00:00:00 ps -aF
> 
> $ git version
> git version 1.6.4.4
> 

Looking at the code of gitk, I believe the git diff-tree process is
spawned by proc getblobdiffs (gitk-git/gitk:7322). It sets up a command
that matches all the arguments I see in the above ps -aF listing
(gitk-git/gitk:7335):

set cmd [diffcmd $ids "-p $textconv -C --cc --no-commit-id -U
$diffcontext"]

It then seems to setup this command to be run and the output processed
via proc filerun (gitk-git/gitk:7352):

filerun $bdf [list getblobdiffline $bdf $diffids]

I am not very familiar with TCL. Is there a standard/correct way to
pre-maturely halt this filerun processing? It seems to use the fileevent
to know when there is more data to process.

A Google search turned up a way to get the PID from $bfd and said that
on unix systems you could run a kill, but that TCL had no built in kill
mechanism. This seems a bit hackish/non-cross platform. Is there a
better mechanism? Would something like closing the file descriptor cause
the filerun processing to finish and the git diff-tree to terminate with
a broken pipe?

Thank you,
David

-- 
David G. Holmer, Ph.D.
dholmer@persistentsystems.com
CTO and Co-Founder
Persistent Systems, LLC
www.persistentsystems.com
Office: 212-561-5895
Mobile: 650-533-4964
Fax: 212-202-3625