pynotify corrupted double-linked list?

[Antoine Martin]

I have seen this sort of crash before (usually on shutdown with control-C), but this seems to happen during runtime which is more problematic...
The ​original bug (was on the wrong tracker) says this happens on clicking "Apply" in the options window (I assume the main 'Configuration' dialog - not the server options?).

I first thought that this was due to pybonjour, but the backtrace also seems to point to pynotify (and gio/dbus) - maybe we need an idle_add call on the notify path?

[Antoine Martin]

crash report

[Antoine Martin]

gdb backtrace

[Antoine Martin]

Please try the attached patch and let me know if that fixes it.

I think pynotify may be broken when used from within the gtk main loop - no idea why.
Using dbus directly (which is the underlying mechanism) seems to fix this problem.

[Antoine Martin]

use dbus for notification ahead of pynotify

[pmarek]

I can reproduce that with debian testing/unstable.

ii  winswitch  0.12.6-1        Tool to start and control remote sessions,
ii  xpra       0.0.7.30+dfsg-1 tool to detach/reattach running X programs

# uname -a
Linux cacao 3.1.0-1-amd64 #1 SMP Thu Nov 3 19:35:59 UTC 2011 x86_64 GNU/Linux

[Antoine Martin]

Does the patch fix the problem? (you will need dbus-glib and dbus-python installed, probably are already)

[pmarek]

After applying the patch I still get a crash.

[pmarek]

GDB report after patching

[pmarek]

last lines after patching

[pmarek]

Data above is after patching, when going into the configuration and unchecking the "start local server" flag => apply.

[Antoine Martin]

Hah, this latest stacktrace now points to pybonjour and not py-notify..
Until I find a way to fix this, you should be able to workaround this particular crash by completely disabling mdns:

mdns_listener=False

in .winswitch/client/client.conf
and:

mDNS_publish=False

in .winswitch/server/server.conf

I would be very interested to hear if you still get the crash with/without the winswitch-dbus-notifications.patch patch above as this would give me a clear indication as to whether this is going in the right direction or not.

[pmarek]

Without the patch I get this:

*** glibc detected *** /usr/bin/python: malloc(): smallbin double linked list corrupted: 0x000000000376da70 ***

When disabling mnds, it works, and the patch makes no difference.

[Antoine Martin]

The dbus notification patch was accidentally applied as part of r4479 (oops)... Will test this further on all the platforms that use pynotify/dbus. Not reverting since I think it is worth having already as it reduces the glibc corruptions I have seen on shutdown.

The next part is to replace ​pybonjour (which is unmaintained...) with a dbus approach, at least for *nix platforms that have avahi/dbus.
Basically going back to the approach that existed in versions up to ~ 0.8.x: use avahi if present and fallback to pybonjour if not (osx, win32, ..)
Some pointers:

• r1626 removed the old avahi code, may re-instate some of those classes..
• ​twisted + dbus ticket with sample code
• ​python + avahi/dbus example code
• ​more example code

[Antoine Martin]

r4481 re-instates the avahi bindings and seems to get rid of the double linked list corrupted issue here (although I was only seeing it on control-C shutdown - not during normal use)

Please let me know if that fixes it for you so I can make a new release with this fairly important crash fix.

Still TODO:

• detect mdns_remove in avahi code (resolve_error?)
• tell dbus we are no longer listening when shutting down
• add python-avahi to deb/rpm dependency list

[pmarek]

$ apt-get remove winswitch
$ svn info
...
Revision: 4481
$ sudo python setup.py build
$ sudo python setup.py install
...
byte-compiling /usr/local/lib/python2.7/dist-packages/winswitch/ui/notification_util.py to notification_util.pyc
/usr/local/lib/python2.7/dist-packages/winswitch/ui/notification_util.py:148:
  SyntaxWarning: name 'haspynotify' is used prior to global declaration
  global haspynotify
byte-compiling /usr/local/lib/python2.7/dist-packages/winswitch/ui/quick_connect.py to quick_connect.pyc

winswitch_applet does now run without the check mark at "start local server", even if MDNS is activated again. And: it starts much faster!

Thanks a lot.

[Antoine Martin]

Thanks for testing!
I will make a new release shortly with this fix.