Thread problem causing some calls to hang for 25

[Thiago Macieira]

Em Terça-feira 18 Maio 2010, às 19:47:29, Thiago Macieira escreveu:
> Em Terça-feira 18 Maio 2010, às 17:00:51, Thiago Macieira escreveu:
> > QTBUG-7475 is still not fixed. I'm investigating a bit more with
> > helgrind.
> 
> That bug is a different issue.
> 
> It's a very basic race condition in protected_change_timeout (dbus-
> connection.c). The code there unlocks the connection in order to call out
> to binding code. However, the moment that it unlocks, another connection
> may acquire the lock. When it reaches the same function, timeouts is NULL,
> so it will immediately fail.
> 
> That causes dbus_connection_send_with_reply (and and_block) to fail.
> 
> I see two solutions, neither of which pleasant:
> 
> 1) loop inside protected_change_timeout until the "timeouts" structure
> reappears, by unlocking and relocking the connection (with a yield or sleep
> in-between).
> 
> 2) don't drop the lock, but call out to binding code with the locks held in
> place. We can document that these callback functions need to be
> deadlock-safe.

Turns out Havoc had already prepared a patch for case #2 and even documented.

See https://bugs.freedesktop.org/show_bug.cgi?id=17754 and 
http://lists.freedesktop.org/archives/dbus/2008-January/009100.html

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
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