Tablet Python #4 - Sources of Memory Leaks

Marius Gedminas blogged an interesting article about memory leaks in Python. On the tablet you don't have much memory available, so memory leaks will annoy the users very quickly.

Python is a garbage-collected language (like Java or C#), so memory leaking is normally not an issue, but there are situations where you should be careful.

Bindings to C libraries

Many modules are bindings to C or C++ libraries, and memory leaking is unfortunately quite common in those languages, esp. in complex libraries. A hot candidate for memory leaking on the maemo platform are the GdkPixbuf operations.

GdkPixbufs get not automatically garbage collected by Python. Always use del on a GdkPixbuf explicitly when you don't need it any longer.


The __del__ destructor method

Classes can have some sort of destructor method in Python.

  def __del__(self):
  
      ...

This is called when you use del on the last reference you are holding. But be very careful! Classes overriding this destructor method are not eligible for breaking reference cycles by the garbage collector anymore! They have to be released manually. It's normally not necessary to override the __del__ method, so you better stay away from it.

Always take special care when dealing with classes overriding the __del__ method. Cyclic references involving such classes cannot be resolved by the garbage collector automatically.

Syndicated 2008-06-12 14:32:00 (Updated 2008-06-12 16:21:29) from Martin Grimme

MediaBox 0.95 released

The new version 0.95 of the MediaBox Media Center is finally available. Thanks to all users who reported bugs and made suggestions for new features. Thanks to lot of feedback, many things have improved since the last release.



With the new MediaBox you can finally compose playlists and rearrange them on the fly. If your internet tablet has a keyboard connected, you can also search for tracks in long playlists or albums by just typing a few letters of the title.



The new version has an improved easy and finger-friendly user interface and reduces memory consumption, especially when dealing with large collections of media.



You can view the release notes at http://mediabox.garage.maemo.org/data/release-notes.

MediaBox 0.95 is available in the Maemo Extras repository. Click the arrow below for quick install.



Have fun!

Syndicated 2008-05-09 19:06:00 (Updated 2008-05-09 19:15:03) from Martin Grimme

MediaBox Walkthrough: Search as You Type

Today I'm showing you another new feature of the upcoming version 0.95 of the MediaBox Media Center. Search-as-You-Type works on any internet tablet with a keyboard, either built-in or connected via Bluetooth or USB.

Find a track
If you have many tracks in an album or the playlist and want to quickly scroll to a particular track, just type some letters from its title.

While typing, MediaBox searches your tracks for a match and scrolls the list to bring the track into view. You can see your search term displayed in the title bar while typing.



You don't have to type the full title as it's sufficient to type just a few subsequent letters from anywhere in the title.

Make a new search
The search text field clears automatically after a few seconds.

In order to make a new search, wait for the search text to disappear in the title bar, and enter your new search term.

Syndicated 2008-05-02 20:10:00 (Updated 2008-05-02 20:15:22) from Martin Grimme

Mediabox Walkthrough: Playlist Editing

In a few days the new version 0.95 of the MediaBox Media Center will be released for the Nokia internet tablets. Let me introduce a few of the new features until then. Today I'm showing you a bit about the new playlist feature.

Enter the music viewer

You can edit the playlist in the music viewer. To get there, press on the tiny arrow button in the bottom left corner once.

The screen will slide up to reveal the viewer menu where you can switch between the different viewers of MediaBox.

Tap on the music viewer icon to select it. You're in the music viewer now.

Choose an album

On the left-hand side of the screen you can see a strip of images representing your album folders which MediaBox has found on your device.

You can drag the strip with your thumb to scroll through it.

When you've found the album you're looking for, press on the little arrow button on the album image to open it.

Add tracks to the playlist
After opening an album, you can see all its tracks on the screen. Again, you can use your thumb to scroll through this list.

The top item of this list represents the album itself and shows you the album cover (if available) and the number of tracks in the album. The other items represent the tracks in the album.

On each track there is a menu button to the right. Tap on it to reveal the track menu, where you can choose between [play] and [add to playlist]. The album item does not (yet) have a menu button. Instead it has the [add to playlist] button there.

That way you can either add particular tracks or complete albums at once to the playlist.

Switch to the playlist view

There is a button in the toolbar where you can switch between album view and playlist view. Press it once to get to the playlist view.

The playlist view shows all your playlist items in a list. Use your thumb to scroll through this list.

The album cover on the left side of each playlist item shows you where this particular track comes from.

Play or remove tracks

Each playlist item has a menu item on the right-hand side.
Press it once to reveal the item menu, where you will find buttons for [play], [remove from playlist], [remove succeeding], and [remove preceeding].

The [remove succeeding] and [remove preceeding] buttons are special because they do not only remove the selected item, but also all items preceeding or succeeding it.
That way you can quickly clean up large portions of the playlist.

Reorder the playlist

You can use your thumb to drag playlist items in order to reorder them.

Use the tiny dragging area at the left of an item to drag it around.

Syndicated 2008-05-01 16:07:00 (Updated 2008-05-01 16:27:26) from Martin Grimme

Laptop, External Monitor, and xrandr to the Rescue

I have just upgraded to Ubuntu Gutsy (I know I'm very very late) on my laptop. The installation went fine but when I connected an external monitor with a higher resolution than my laptop has, gdm and GNOME were not able to detect this, and instead displayed the picture in the upper left corner of the screen.

This was especially funny with GNOME, because the desktop actually used the full resolution, and I could move windows over the whole screen. Only the panels were stuck in the middle of the screen.

Apparently I'm not the only one with this problem, so let me tell you what I found out and how to fix this.

Everything was fine with Ubuntu Feisty. When I connected an external monitor, the laptop screen switched off and the higher resolution was used. But now when I connect an external monitor, the laptop screen doesn't switch off automatically.

Because the laptop screen is still on, the system now has two screens and GNOME will automatically adapt to the screen with the lower resolution.

The moment I manually switched off the laptop screen with the tool xrandr

$ xrandr --output LVDS --off

the GNOME panels jumped to their correct position. So let's investigate this xrandr a bit more.

xrandr is a powerful tool for managing multiple video outputs, rotating the screen, and setting up multihead displays.

You can get a list of what the graphics driver thinks it has connected by invoking

$ xrandr -q

This will give you something like this:

Screen 0: minimum 320 x 200, current 1680 x 1050, maximum 1680 x 1200
VGA-0 connected 1680x1050+0+0 (normal left inverted right) 433mm x 271mm
   1680x1050      60.0*+   60.0  
   1280x1024      75.0     59.9  
   1440x900       75.0     59.9  
   1280x960       59.9  
   1152x864       74.8  
   1280x720       59.9  
   1024x768       75.1     60.0  
   800x600        75.0     60.3  
   640x480        75.0     60.0  
   720x400        70.1  
LVDS connected (normal left inverted right)
   1024x768       60.0 +   60.0  
   800x600        60.3  
   640x480        59.9  
S-video disconnected (normal left inverted right)

The interesting entries are LVDS (the laptop screen) and VGA-0 (the external monitor). Both are connected. VGA-0 might be called VGA or similar on your system, as this name is driver-dependent.

If I wanted to check if an external monitor was connected, I'd just run

$ xrandr -q | grep "^VGA.* connected"
  
VGA-0 connected 1280x1024+0+0 (normal left inverted right) 338mm x 270mm

I want the system to switch off the laptop screen whenever an external monitor is connected, so that GNOME will use the higher resolution. This easily can be done by adding the following lines to /etc/gdm/Init/Default just before the

exit 0

line:

xrandr -q | grep "^VGA.* connected" >/dev/null
RC=$?
if [ $RC = 0 ]; then
  xrandr --output LVDS --off
fi

It will also make gdm use the full resolution.

Syndicated 2008-03-26 09:14:00 (Updated 2008-03-26 09:21:24) from Martin Grimme