Leak Debugging Screencasts
L. David Baron (dbaron@dbaron.org)
I was asked to record some screencasts showing how I debug memory
leaks so that other people could understand better how I use our memory leak
debugging tools. So I've been recording (and talking) while I'm
debugging memory leaks.
These are listed in the order I made them. Many of them probably
aren't particularly interesting at all. First, I'd recommend reading
the overview of
our memory leak tools. Then:
- For debugging of small sets of reference-counted objects with the
refcount balancer, watch session 6 and then session 7.
- For debugging using trace-malloc [need screencasts]
- For debugging using leaksoup [need screencasts]
- For debugging using diffbloatdump [need screencasts]
- For debugging using DEBUG_CC (which you should use for leaked
global window objects), look at session 3 for now, although it leaves a
bit to be desired (see below). And maybe session 4-5, although it's one
of the most confusing leaks I've debugged in the past few years.
- For running the current tinderbox leak tests, see sessions 1 and
2
The screencasts
- Leak Debugging Session 1
(10 MiB, 6m24s, recorded 2007-08-29T22:03-07:00)
- An attempt to debug the
RLk being nonzero on the Mac
tinderbox. Demonstrates basic use of XPCOM_MEM_LEAK_LOG
and running the tinderbox leak test. I couldn't reproduce the
leak.
- Leak Debugging Session 2
(13 MiB, 8m17s, recorded 2007-08-30T12:00-07:00)
- Another attempt to debug the
RLk being nonzero on the
Mac tinderbox. Demonstrates basic use of
XPCOM_MEM_LEAK_LOG and running the tinderbox leak test.
Again, I couldn't reproduce the leak.
- Leak Debugging Session 3
(89 MiB, 1h00m40s, recorded 2007-08-30T17:44-07:00)
- An attempt to debug bug
393898. But I made a mistake a few minutes in, as
described here, and ended up debugging something that wasn't
actually leaking in the case I was debugging. However, it was leaking
in another important case, and I found that by code inspection, so I
ended up fixing bug
342600 as a result. This shows a bit about how to look at
DEBUG_CC output and quite a bit about how to poke at
JavaScript objects in the debugger to figure out where they were
created.
- Leak Debugging Session 4
(21 MiB, 14m31s, recorded 2007-08-31T14:22-07:00)
- Leak Debugging Session 5
(63 MiB, 45m49s, recorded 2007-08-31T14:43-07:00)
- [Two screencasts that should have been one.] As a followup
to bug
342600 comment 10, and perhaps also related to the real bug
393898, I debugged why DOM Windows didn't go away when closing the
addons window. I eventually filed bug
394514 with my findings, although it's pretty closely related to the
existing bug
387491. This one is probably the most confusing so far; I spent
most of the time I was recording it being confused; the underlying
problem is in some sense a deficiency of the cycle collector.
- Leak Debugging Session 6
(43 MiB, 27m05s, recorded 2007-08-31T17:37-07:00)
- This is a pretty clean demonstration of how to debug a simple leak
using the refcount balancer. It involves only XPCOM_MEM_REFCNT_LOG and
not XPCOM_MEM_COMPTR_LOG, though. And the leak itself is potentially a
little bit confusing due to XPCOM aggregation. But it's
probably a good first screencast to watch. The leak is bug
394528.
- Leak Debugging Session 7
(50 MiB, 35m56s, recorded 2007-08-31T21:29-07:00)
- A bunch more use of the refcount balancer. I moved more quickly
through things, and used the refcount balancer in rapid succession on
about 6 different objects. Probably a reasonably followup to the
previous session. The leak is bug
394542.
How I made these
I installed pyvnc2swf
on my Fedora 7 machine. I also needed to install pygame and tkinter
RPMs for this to work. I also installed audacity (from Fedora) and
lame-libs (from Livna).
Then I made the screencasts in four steps:
- Connected with vncviewer to the machine I was debugging on (in this
case, an ssh tunnel from localhost:5900)
- /usr/local/pyvnc2swf-0.9.3/pyvnc2swf/vnc2swf.py -o leak6-raw.swf -S
"arecord -r 22050 leak6-raw.wav" localhost:0
- Use audacity to convert the WAV to MP3 (File → Open; File
→ Export As → MP3)
- /usr/local/pyvnc2swf-0.9.3/pyvnc2swf/edit.py -a leak6-raw.mp3 -l -K
500 -S 1.0s -o leak6.swf leak6-raw.swf