Older blog entries for ensonic (starting at number 111)

GObject reference counting

Last month I made good progress on the undo/redo. I am now running the undo/redo in sync with the object lifecycle. The downside of this is that undo/redo fails when you have ref-count leaks. This now makes them more apparent. When trying to debug them I noticed that refdbg is not working anymore since quite a while. I was googling what other people use for such problems. Well, apparently everybody hates ref-count issues. Also most of the info you find is how to get traces for refcount activity. That is what refdbg does also. As this did not work for me anymore I've tried systemtap. Unfortunately right now its not useful for user-space work on most distros (except fedora) - bugs filed. Next step: gdb scripting. I managed to get a gdb script running. Now even for simple cases you quickly end up with a log of 150 backtraces. That is a lot to manually review. I went one step further and wrote a script to filter the traces. Over time I got the trace-log down to 20 entries. This is practical. Unfortunately the gdb script only work for tracing the lifecycle of one particular object. If I extend it to work for all refcounting activity I hit a gdb limitation to not allow nested commands :/. Back to refdbg :) I finally figured why it does not work and have started to fix it up. Lets see how far I get next month.


Naturally this used most of my hacking time. Still I managed to make some progress there as well. The buzztard irc channel was much more active this month. People reported small things here and there and most of it got fixed right away. The manual got some more love too to help people to get started and improve the description of several concepts. Finally all the refcount-debugging leads to a lot of code reviews. I found several areas with lots of needless refcount activity - fixes are in the repository.

81 files changed, 2682 insertions(+), 817 deletions(-)

gstreamer projects

In October I had not much time for buzztard. I went to the GStreamer conference and the CELF Europe. There I gave a talk about the "MeeGo multimedia stack". I also hacked on two GStreamer tool projects; gst-tracelib and gst-mediainfo. In tracelib I worked on a UI to monitor gstreamer pipelines on the fly. My approach to use libgvc (graphviz) for the layout seems to challenge it a bit though - I get very mysterious failures. At some point realloc is failing to e.g. allocate 96 bytes and the lib calls abort(). mallinfo() from libc is telling that the process uses 200 mb and valgind has nothing serious to complain about. That's weired as I was suspecting a corrupted memory list. I have to put that aside for a while until I get some new ideas for tackling it.

gst-mediainfo is the UI for the new discoverer API in GStreamer. I'll make a first release when the current gstreamer core and base is out as it depends on them.

In buzztard I mostly worked a bit on the crash recovery and did some bug fixing. Hopefully will have more time in November.

14 files changed, 325 insertions(+), 166 deletions(-)


After all the initial work for journaling of edit events in the editor, I wanted to get a first proof of concept that everything fits together. And that I just got. The pattern editor implements a change-logger interfaces. It grabs the changelog singleton instance and logs all changes together with the undo action. The redo-action gets serialized and written to the changelog. The ui can undo/redo activities by using the change-logger interface. Upon startup the ui checks for leftover change logs, auto-cleans a few of them and offers a dialog for deleting/replaying them. I can now load a song, make changes in the pattern editor, ctrl-c/kill the app and replay the log when starting it again. There are a couple of details that need to be cleanup and some things need a bit more thinking: Next I will implement this in larger scale also.

As a continuation from last month I changed the whole editor UI to use G_DEFINE_TYPE and co. Boring work, but good to have it done now.

I had some strange crashes in the test suite - all pointing to gconf and only happening with the commandline client. After adding lots of extra logging there I still could see nothing wrong. Then I remember the hack I added to get a eventloop into the app - I run it as a new thread. By doing that I was doing gconf bits from different threads too and it does not seem to like it. I have now done the mainloop stuff more properly and get no more crashers. While looking into this problem, I cleaned the settings classes and the gconf backend a bit. It now does more stuff only as needed, improving the startup time of buzztard app a little further.

In GStreamer next core release will have extra metadata on element factories. This mechanism allows me to kill the one-property help interface. I rewrote all the code to use that conditionally and will remove it in a year or so.

As a last bigger task I migrated from deprecated HAL to GUdev. I have still conditional support for both, but will kill the HAL code once everything works nicely. I was using hal to discover input devices (joysticks, wiimotes,..) and midi-devices that can be used to control effects. Most of the conversion was straight forward. I spent a bit more time on getting nice names of the found devices for the UI and to classify midi-devices. For the midi-device classification I copied the matching rules from HAL - after all they seemed to do the trick there. For the ui names HAL was actually grepping through various files (e.g. /proc/asound/cards) for soundcard names. That I did not really wanted to copy. I got some great help from the udev people and learned that udev devices have properties like ID_VENDOR. One just needs to walk the device tree to get to the root device and grab the names there.

119 files changed, 3377 insertions(+), 1953 deletions(-)

tracking down udev hangs

I still face some problems on my new computer system. One of them iswas that udev was hanging in 8/10 cases at bootup. Thanks to great support from the udev folks I learned how to track it down. I previously tried to add options to /etc/udev/udev.conf (e.g. to raise the log level), but one can actually just add them to the kernel options. This has the great advantage that they don't persist. Things you want to add to debug are:

udev.log-priority=info udev.children-max=1 udev.exec-delay=1

This logs a lot of things (the boot can go from 30 second to minutes, so be patient). The option children-max is turning parallel event execution off and exec-delay is delaying run actions. With those I saw that the system hangs when loading the cdrom.ko kernel module. As I had some problems with the drive as well I swapped it and now bootup is fine.

working on multimedia for MeeGo at Nokia

If you like to work on free software and like snow - we're having a few open positions:

Ping me on irc (ensonic @ freenode/gimpnet) if you have questions.

After some more work bt-dec starts to works better. I can now play buzztard songs in totem, banshee and co. I still see some issues with seeking though.

I have be going through my pending gtk bugs and patches. I can see a lot of activity in gtk+ these days. People have been helpful reviewing and commenting the changes. I could close two of my bugs with patches to code and docs committed. At the same time I also understand a few things better and reworked the focus handling on the tabs. Instead of listening to focus notifies and then grabbing the primary widget on the page, I am now overriding the focus vmethod and grab there. The disadvantage of the previous method was that the widget has to be realized and mapped, but when you receive the notify for the tab switch, it is not necessarily the case yet.

There were some changes on the logging in gstreamer. I had to adjust some parts of my tests that where intercepting log messages.

I've started to migrate all modules to use G_DEFINE_TYPE, G_DEFINE_INTERFACE and GST_BOILERPLATE macros to shorten the code. I hope I can finish it next month. At the same time I have cleaned-up my gobject use:

  • remove dummy vmethod implementations (empty property setters/getter)
  • no need to check for dispose/finalize in parent class (just chain up, they always exist)

I improved the error handling in the commandline client and also in the ui (when rendering to disk). It catches and handles missing element messages now. Before the processing could hang if that happened :/

While doing more work on the changelog I noticed that I could also use that to show last save date when warning about unsaved changes. The change log uses UTC timestamps, so I had to convert them. I haven't found any nice API for this (like give a date and tell what tz it is and ask to convert to local or any other tz). The startup check for old change logs does now some auto cleanup and sanity checks. Next I'll add some ui for picking one for recovery.

I recently upgraded on machine to suse 11.3. After that all machine icons where in the wrong size. After some digging I noticed that the gnome/index.theme misses all the 'scalable' entries and that seems to break my svg icons. I have added a workaround, but with that I get 48x48 png scaled up. Readding the missing entries works. I filed a bug, but nobody feels responsible so far :/

Bored from all the refactoring and bug fixing I hacked a bit on the spectrum analyser. Its now using cairo (no more gdk_draw_*) and thus is ready for gtk3 and looks much nicer. In addition is can do log plots and one can increase the resolution.

While playing with orc for gstreamer and googling for simd information, I can across some info about the gcc autovectorizer. One can ask for quite verbose reports of gcc attempting to use simd for loops. I could improve the performance in a few place based on the reports. Unfortunately the only places where the vectorization finally succeeded where those where I just should have used memset() :/

78 files changed, 4300 insertions(+), 1832 deletions(-)

Lintian complained about missing man-pages for buzztard binaries. I also had a pending bug for gtk-doc to clarify how one can do man-pages. Last month I wrong some docs about how to document binaries in docbook as well, so that the information is in the api-docs, but one can also generate man pages from the same source. The new guides are not yet on library.gnome.org, but it can be found in git.

I continued with more undo/redo hacking. I have again more tests that all pass and working undo/redo in pattern editor for trivial operations. Need to do edit-groups next and work more on the journal replay part. The testing work resulted in some local check improvements - the BT_CHECKS env-var supports globbing to select tests. Also patched that for gstreamers GST_CHECKS env-var.

While showing buzztard to a colleague I noticed that the audio settings where not used for the sample players. Fixed in svn.

In the early days I made some mistakes in the xml design of the song format. Some tags had different attributes depending on their parent. This makes it impossible to do xsd schema validation. I have changed the song xml slightly (with backwards compatibility of old songs) and now xsd validation works.

Finally I have started buzztard-bin. This is supposed to be a gstreamer plugin that plugs a whole buzztard song, so that one can play that in e.g. totem. The basics are there, should be working quite soon.

83 files changed, 2452 insertions(+), 624 deletions(-)


The packaging continued - I found a Gentoo overlay that has buzztard packages, as well as packages for Arch Linux. The later brought up some issues as arch Linux uses --as-needed when linking. An article in the Gentoo documentation suggests that its not a good idea to use this by default. To cut the long story short - normally (without that option) the order of libraries in the linker invocation did not really matter. When using --as-needed only libraries that are actually used are linked in. To make that work one has to put needed libraries behind libraries that need them. If you want to try this on your own software: LDFLAGS="-Wl,--as-needed" ./autoregen.sh

The Debian packages that have been made recently are nice too. All packages undergo various checks, among a spell-checker of strings in binaries.

As planned I worked a bit more on undo/redo. I have it now implemented and in use for some case in the pattern editor. I also added unit tests to verify the stack logic.

I also managed to finished some work I had started at the Linux Audio Conference - copy and paste of machine parameters between patterns and the machine property window.

54 files changed, 2174 insertions(+), 699 deletions(-)


It is nice to see that more and more distros have buzztard packages. Many thanks to Sebastian Dröge for submitting packages to Debian and Ubuntu.

Latest GStreamer releases (gst-plugins-base-0.10.28) have my adder fixes. With those trick playback in buzztard works much better. Scrubbing is not locking up any more and we can play the score forward and backward at different speeds. There seems to be still an issue in more complex songs though. Every time the playback accelerates, the sink is waiting for something and thus there is a pause.

One major feature I'd like to have for 0.6 is undo/redo and journaling. The latter is important to minimize the loss of data in case the application or the system crashes. I have been thinking for quite a while how to implement it and came to the conclusion that it can be made so that journaling means having a serializable redo stack. I have now started to write the code for it. Hopefully more news on how it went soon.

48 files changed, 2240 insertions(+), 351 deletions(-)


I will give a talk about "Writing audio applications using gstreamer" at the Linux Audio Conference 2010. Naturally quite some time went for writing the article. Now that it has been accepted, I need to start working on the slides and demos.

In buzztard I've tried to make the life of people that use jack or pulse a bit easier. The problem here is that the player is only visible in jack/pulse when it is actually playing. I have now some code that keeps the sink alive (in GST_STATE_READY). This allows e.g. changing the volume in pulse or routing the output in QJackCtrl even if the app is not playing. Unfortunately it only works after the sink was in playing once. I need to confirm my theory of what wrong still.

I recently brought a netbook (MSI L1300) and thus wanted to try buzztard on this machine. I have installed moblin 2.1 on it to play with moblin. As usual, installing own software on a new linux distro/machine always brings up something. After a few rounds of configure maintenance and dependency trimming I am set and having it running. Performance seems to be okay even for complex songs. Yay!

Besides that, I fixed a few more bugs and wrote more tests.

gtk-doc, xslt and profiling

As part of the endless journey of getting gtk-doc to spit out the docs faster I managed to get xsltproc from libxslt to output full callgraphs. The output is compatibe with oprofile and thus the same tools to rendering can be used (e.g. gprof2dot). Bit sadly me profiles hit a python assertion in the above code which I have to disable to run it, buug filed but dormant since 1 month. Same for the xsltproc patch, the patch and an example image is here but no reviews so far.

Now the way to make gtk-doc faster would be to make the xslt faster and as I can see from the profile, this could be done, by preprocessing the xsl with some variables set. Right now I have not too high hopes on this as libxslt seems quite dormant and this is not so straight forward :/

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