Work Configuration

Inspired by Nicholas Nethercote’s description of how he sets up his tracemonkey work environment, I thought I’d describe my work configuration and how it differs from njn’s.

Like Nick, I work almost entirely off of the tracemonkey tree these days, and mostly within js/src. I don’t use the js shell all that much compared to the full browser, though, so I tend to do things with the whole tree.

working repositories

Similar to Nick, I have a ~/src/ directory populated with clones of the tracemonkey repo. I have one, “TM-upstream/”, that follows the upstream tracemonkey repository. In fact, I use cron to pull updates hourly. The rest are created as clones of TM-upstream, or sometimes of each other. I vary in how I create these. Some are created via ‘hg clone TM-upstream TM-whatever’, although for whatever reason I usually do ‘cp -rlp TM-upstream TM-whatever’ and then edit TM-whatever/.hg/hgrc to change the ‘default’ path to TM-upstream. The ‘cp’ method is faster, but the end result is pretty much the same. Sometimes I copy the mq subdirectory (.hg/patches) from the repo I’m cloning, sometimes I create a new one from scratch. And sometimes I don’t use one at all.

Oh, and with emacs I had to do

  (setq vc-make-backup-files t)

to make it break hardlinks when modifying files. Breaking hardlinks is normally the default, but it seems like vc mode has a different default that is really really bad if you’re using ‘cp -rlp’ to clone your repos.

All of my (tracemonkey-based) repos start with “TM-“, probably because I use my src/ subdirectory for checkouts of various other projects (bugzilla-tweaks, archer-mozilla, archer, firebug, addon-sdk, etc.). Not all of those are hg-based; I have several git repos and even an svn checkout or two. For the Mozilla tree, I tend to only actively use one or two repos at a time; the rest are for dormant unfinished work.

I made a shell function ‘pullup’ that does ‘(cd $(hg path default) && hg pull)’, which goes to the default upstream repo (probably TM-upstream, unless this is a clone of a clone) and updates its objects. (Note the lack of a -u; I don’t want to update the working directory for the upstream repo without a good reason.) To update my working repo, I’ll ‘hg qpush -a’ to apply as many patches as I can, then probably ‘hg qpop’ to pop off the last one because it failed. (I tend to have a small pile of heavily bitrotted patches lurking around at the end of my series file.) Then I’ll do ‘pullup’ to update the upstream repo and ‘hg pull –rebase’ to merge the changes into my patch queue. My ~/.hgrc sets my merge tool to kdiff3, so any conflicts will pop up the visual merge editor.

I push changes directly from my working repo by using

  hg qpop
  hg show | head
  hg qref -e # if needed

to fix up the commit messages, then qpush everything back on that I’m committing. (I tend to break up my commits into at least 2 pieces, so I usually push more than one change at a time.) Then I do ‘hg qfinish -a’, do my last round of testing, and ‘hg push tracemonkey’ (tracemonkey is set in the [paths] section of my ~/.hgrc).

I don’t bother to run ‘hg outgoing’, because I only commit patches that I’m about to push. I suppose if I were collaborating with someone else, I might get some extra crud that I’d need to worry about, but so far I’ve always done that through patches imported into my patch queue.

object directories

I place my object directories underneath the source directory, so that I can use hg commands while my working directory is underneath the object directory. I mostly use plain ‘~/src/TM-whatever/obj’, which is almost always a debug build. If I need an opt build, it’ll be ‘obj-opt’ in place of ‘obj’. Rarely, I’ll make ‘obj-somethingelse’ for special purposes.

Prefixing things with ‘obj’ helps when moving stuff between machines, because I can do

  rsync -av --exclude='/obj*' TM-whatever desthost:/some/where


When underneath obj/js/src, I’ll just run ‘make’ or ‘make -j16’ or whatever to rebuild (even when testing with the browser, because my mozconfig always has ‘ac_add_options –enable-shared-js’ so rebuilding here is enough. In fact, I tend to forget to remove it when making opt builds for performance testing.)

I also tend to modify things in js/jsd and js/src/xpconnect/src, so I have a special makefile that does a minimal rebuild for those:

ROOT := $(shell hg root)

 $(MAKE) -C $(ROOT)/obj/js/src
 $(MAKE) -C $(ROOT)/obj/js/jsd
 $(MAKE) -C $(ROOT)/obj/js/src/xpconnect/src
 $(MAKE) -C $(ROOT)/obj/layout/build
 $(MAKE) -C $(ROOT)/obj/toolkit/library

I have that saved as ~/mf, and I have a shell alias ‘mk’ that does ‘make -f ~/mf’. So I’ll make my changes, then run ‘mk -k -j12’ or whatever. (I don’t know why I bother to give numbers to my -j options, since I use distcc’s hosts syntax for limiting concurrent jobs anyway.)

Even lazier, I have my emacs set up to pick the right make command depending on what directory I’m in (please excuse my weak elisp-fu):

; Customizations based on the current buffer's path

(defun get-hg-dir (path)
 (if (equal path "/")
 (if (file-exists-p (expand-file-name ".hg" path))
 (expand-file-name ".hg" path)
 (get-hg-dir (directory-file-name (file-name-directory path))))))

; For Mozilla source:
;  - if within an hg-controlled directory, set the compile-command to
;      make -f ~/mf...
;    which will do a fairly minimal rebuild of the whole tree
;  - unless we're also underneath js/src, in which case, just do a make
;    within the JS area
(defun custom-compile-hook ()
 (let ((path (buffer-file-name))
 (dir (directory-file-name (file-name-directory (buffer-file-name)))))
 (if (not (null (get-hg-dir path)))
 (if (string-match "js/src" dir)
 (set (make-local-variable 'compile-command)
 (concat "make -C " (expand-file-name (concat dir "/../../obj/js/src")) " -k"))
 (set (make-local-variable 'compile-command)
 (concat "make -f ~/mf -k -j12"))))))

(add-hook 'find-file-hook 'custom-compile-hook)

I have my F12 key bound to ‘compile, so I just hit F12, check that the command is right, then press enter to build. One problem I have is that our build output is much too verbose, so I don’t notice warnings very well. I keep meaning to shut it up (probably by only printing the file being compiled unless there are errors/warnings), but I haven’t gotten around to it.

compiling: distcc and ccache

I rely heavily on distcc for my builds. I do almost all of my Mozilla work on a single laptop machine, though occasionally I’ll reboot it into Windows to suffer through something there, or use one of my two desktops (one home, one work). My work desktop is quite beefy. My home desktop is less so, but still good enough to speed up builds dramatically. I run a cron job on my laptop to autodetect where I am and switch my ~/.distcc/hosts symlink to the appropriate hosts file, which contains “localhost finkdesk/12” at work and “localhost” at home. The /12 and /7 are the max number of concurrent jobs distcc will trigger; I set it lower on my home machine to keep from bogging it down with contending jobs, though honestly I haven’t benchmarked to see what the right numbers are.

About half the time, I’ll have distccmon-gnome running to monitor where the jobs are going to. It’s a quick way to spot when I’m sending things to the wrong place (eg when I’m VPNed into the work network and finkdesk is reachable; if I accidentally send things there, distcc will slow everything down because the network time way outweighs the compilation speedups.) Or, more often, that something’s messed up and all builds are going to localhost. Or that I’m only getting a single job at a time because I forgot to use -j again.

I also use ccache at all times, but I don’t do anything nonstandard with it. Just be sure to set CCACHE_PREFIX=distcc and allow it to get big with ‘ccache -M’.

linking: gold

When I’m working outside of js/src proper, I also like to use the gold linker in place of the default binutils bfd linker. I’m on Fedora 14, so to switch to gold I do

  cd /etc/alternatives
  rm ld
  ln -s /usr/bin/ ld

(and to switch back, link to ld.bfd). gold takes my minimal links from 30 seconds to about 10 seconds, which is really nice. Unfortunately, I frequently have to switch back to ld.bfd due to incompatibilities. elfhack and valgrind are the usual offenders. Update: According to jseward, valgrind >= 3.6.0 should work fine. Yay! (I currently have 3.5.0).

patch queue

While they’re in my mq, all of my patches are labeled with the bug number and a brief description. When I’m reshuffling changes between my various patches, I create temporary patches whose names are prefixed with “M-” (for Merge) to indicate that I’m planning on qfolding them into some other existing patch. I also use “T-” for temporary patches (debugging printouts or whatnot). It helps to see the state of everything with a glance at my ‘hg qseries -v’ output (which, due to aliases and defaults, I actually spell ‘hg series’).

Very recently, I’ve started using ‘hg qcrecord’ to split up and reorganize patches, and I’m loving it. It’s the same basic story, though — I use it to create temporary to-be-merged patches that I qfold later. I tend to do

  hg qref -X '*'
  hg qcrecord

quite a bit to move stuff out of the current patch (well, the current patch + the current changes on top of it).

disk space

Finally, I also try to occasionally go through all my TM-* directories and run ‘hg relink’ to rediscover what can be hardlinked. It takes a while, so I really ought to cron it. It tends to recover surprisingly large amounts of disk space.

Complete and total tangent:

My underinformed, overopininated take on this is that hg’s disk structures are wrong. As I understand it, the wasted space comes from: (1) you clone a repo, which creates a bunch of hardlinks, using very little space; (2) you periodically update the base repo, breaking many of the hardlinks; then (3) you update the derived repo with those changes. hg doesn’t figure out that it can re-link the object files — which is understandable, since it would need to know for a given file that not only are the latest versions identical, but also that the complete set of revisions between the two repos is identical.

It doesn’t seem that hard for it to figure this out. But even if it did, any local change in the derived repository is going to prevent sharing anyway. That’s what bugs me. Conceptually, hg’s object store is a big pile of byte strings, one for every revision of every file, and each tagged with (and looked up by) its checksum. There’s an optimization that all the revs of a single file can be stored compactly as a set of deltas rather than storing a full (compressed) copy of every rev, but that really ought to be an optimization, not a fundamental data structure. If you ditched the optimization entirely and kept a full copy of every rev, you could trivially share a repo across all of your checkouts. (You could even share a repo with completely unrelated projects, though that’d be more likely to hurt than help.) I would find this much nicer.

Actually, it’s not just that all the versions of a file need to be stored within one filesystem file. hg seems to want the set of versions within a filesystem file to mean something. I would rather have that information (the set of known revisions) stored within a checkout, so that extra revs would be harmless. Then you don’t need to lose the optimization; you can still stuff all revisions into one file, even revisions from completely unrelated branches. You’d even have flexibility to use multiple filesystem files for a single source file, if it has a bunch of revisions that you want rapid access to. (So file1 contains revA + a few deltas, file2 has revB only, file3 has revC + a few deltas, etc. Think images.)

I think I’m probably describing git’s data structures here. If so, it seems like git has it right. Checkouts should have their own state, history, etc., but feed off of a chaotic assortment of checksummed data wads that are optimized for whatever you want to optimize for. It gives much more flexibility.

You shouldn’t even really need to have all revisions stored locally, if you know of a place on the network where you can find old/unrelated revisions when you want them. If you ever ask to jump back 3 years, then sure, it’d take a while to pull down the needed data, but most of the time you’d save lots of disk space for stuff you’re never going to ask for anyway. (And if it bothers you, you can always pull it all down.)

Or maybe I’m wrong about how hg does things.


Ok, that was long. Thanks for making it this far.  Let me know what I got wrong or what I’m doing stupidly. Preferably with a description of your vastly better way of doing it!

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  1. I also pull updates regularly into an “upstream” repo. However I also pull those regularly into my other repos (but without updating of course) and then relink them. In fact I use a changegroup hook to automatically relink after a pull (this from an old version, so not using hg relink).

    changegroup.relink = [ $HG_URL == ${HG_URL#file:} ] || python ~/hg/hg-relink ${HG_URL#file:} .

    I always clone using hg clone; this doesn’t link the working directory, which is better for me because I need to be able to hardlink from my working directory to my objdir, and I don’t want to break those links if I can avoid it.

    I always used to use hg pull -R but thanks to you I can simplify that to hg pull -R `hg path default` 🙂

    I have one clone that I use to push; I set the default-push path in that clone.

    Putting the objdir under the srcdir is bad for me because I use comm-central which pulls in several other repos. If my working directory is in one of the repos then I need to use -R to refer to another repo, but if it’s in an unrelated folder I can just specify the full path to the file in question.

  2. Valgrind 3.6.0 and later should work with and/or be linkable with gold
    — not sure what problem you’re referring to. If it doesn’t, please