Re: XWin crash after the launch of startkde on a remote Red Hat 5 machine

[Jon TURNEY <jon.turney@dronecode.org.uk>]

On 18/09/2010 19:44, michel hummel wrote:
> I have checked the code of the clipboard thread and the race condition
> you talk about should not be a problem.
> Before to start a new clipboard thread, the code waits for the end of
> the first thread (pthread_join) then fixe the variable
> g_fClipboardLaunched = FALSE;
> g_fClipboardStarted = FALSE;
>
> So the new thread will never be launched before the old one has terminated.
>
> I have a proposition of modification to make the clipboard thread more robust.
>
> 1/ Adding a cleanup function which will be automaticaly called at the
> end of the thread.
> I purpose the use of the macro pthread_cleanup_push() pthread_cleanup_pop()
>
> 2/ You said that having a long-lived thread will be a good solution to
> simplify the code.
> I have an other proposition which needs less modification and can
> simplify the code :
> By using also here the macro pthread_cleanup_push() we can
> automaticaly restart the thread on every unexpected exit.
> We just have to delete this restart when the exit is expected (ie.
> End of the function)
> With this solution we don't have to take care about the thread
> being killed by anyone, it will be restarted.

You will need to have some kind of back-off mechanism (i.e. a delay before 
retrying to connect) so that that this doesn't constantly try to connect if 
the server gets into a state where it can't accept the connection or the 
connection is constantly getting closed.

> 3/ An other thing I saw is that when the Xwindow part of the clipboard
> is killed by an other application, the thread will still be alive but
> the clipboard doesn't work anymore.
> A solution can be :
> when an winClipboardErrorHandler() is catched, check for
> this Xwindow window and whenever this window doesn't exist anymore,
> create a new one.

Would it not be simpler to restart the clipboard thread in this situation as 
well, rather than having code to recrate the window?

> What do you think about my suggestions ?
>
> I tested them and they seem to work as expected.
> For example, I skipped the wrapper of XQueryTree (actualy needed for
> xdmcp) and the clipboard is now working with xdmcp/gdm, etc.
>
> If you don't like something in my propositions, please tell me what
> and I will try to adapt it.
>
> If you are interested in a patch doing this, I will be happy to give
> it after a quick review and a clean

That would be great, thank you.

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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