[Okular-devel] TextDocument Multithreading

[Albert Astals Cid]

El Dimecres, 25 de setembre de 2013, a les 23:19:11, Jaydeep Solanki va 
escriure:
> On Wed, Sep 25, 2013 at 11:01 PM, Jaydeep Solanki <jaydp17 at gmail.com> wrote:
> > Running it under helgrind, gives
> > this<https://www.dropbox.com/s/5v3bh1v6le8adkr/helg.txt>output.
> > 
> > It shows a warning near the region where we get a crash saying "*conflicts
> > with a previous write of size 4 by thread #4*", L117 in helgrind output
> > file
> > 
> > Also, can you please throw some light on what the warning is trying to
> > say. What is a 'conflict on previous write' ?
> 
> I read the documentation and understood what it is, but it doesn't give any
> insight about what's going wrong.
> 
> BTW, I tried a few times with helgrind & it didn't crash.

Yeah, it may go so slow that it doesn't really race/crash itself.

I am betting on saying "this is a bug in Qt" but let's prove it first ;-)

My suggestion, do this: Write a simple program that spawns two threads, in 
each thread you create a QTextDocument, add some text to it and then simply 
loop its rendering to a QImage forever.

Let's see if that crashes or not. If not, we can build up from there trying to 
make it more like what Okular does until it crashes.

You up to it?

Cheers,
  Albert

> 
> > On Mon, Sep 23, 2013 at 1:40 PM, Jaydeep Solanki <jaydp17 at gmail.com>wrote:
> >> On Mon, Sep 23, 2013 at 3:17 AM, Albert Astals Cid <aacid at kde.org> wrote:
> >>> El Dilluns, 23 de setembre de 2013, a les 02:05:23, Jaydeep Solanki va
> >>> 
> >>> escriure:
> >>> > On Sun, Sep 22, 2013 at 9:21 PM, Albert Astals Cid <aacid at kde.org>
> >>> 
> >>> wrote:
> >>> > > El Dissabte, 21 de setembre de 2013, a les 23:16:56, Jaydeep Solanki
> >>> 
> >>> va
> >>> 
> >>> > > escriure:
> >>> > > > On Sat, Sep 21, 2013 at 9:25 PM, Albert Astals Cid <aacid at kde.org>
> >>> > > 
> >>> > > wrote:
> >>> > > > > El Dissabte, 21 de setembre de 2013, a les 14:50:50, Jaydeep
> >>> 
> >>> Solanki
> >>> 
> >>> > > > > va
> >>> > > > > 
> >>> > > > > escriure:
> >>> > > > > > Hi,
> >>> > > > > 
> >>> > > > > Hi
> >>> > > > > 
> >>> > > > > > @Albert,
> >>> > > > > > Welcome back :)
> >>> > > > > 
> >>> > > > > Thanks :-)
> >>> > > > > 
> >>> > > > > > As you might be aware GSoC is coming to an end, I want to wrap
> >>> > > > > > things
> >>> > > > > > up.
> >>> > > > > > 
> >>> > > > > > I have a few days, and I want to finish multi-threading
> >>> 
> >>> support for
> >>> 
> >>> > > > > > ePubs
> >>> > > > > > before GSoC ends. I have created a patch, but it crashes
> >>> 
> >>> sometimes,
> >>> 
> >>> > > I'm
> >>> > > 
> >>> > > > > > unable to find a reason to that.
> >>> > > > > 
> >>> > > > > Where's the patch?
> >>> > > > 
> >>> > > > Diff attached
> >>> > > > 
> >>> > > > File to test on :
> >>> > > > link<
> >>> 
> >>> https://www.dropbox.com/s/x63kkjf8q4h4fdy/Getting%20Gold%20by%20J_C_F_J
> >>> 
> >>> > > > ohnson.epub>
> >>> > > > 
> >>> > > > > Do you have a backtrace of the crash?
> >>> > > > 
> >>> > > > I have got two different backtraces, using the same ePub
> >>> > > > 
> >>> > > > Backtrace 1 : http://paste.kde.org/p0b9a1e1e/
> >>> > > > 
> >>> > > > Backtrace 2 : http://paste.kde.org/pa4e31b12/
> >>> > > 
> >>> > > Any reason you have not installed debug symbols for Qt to get a
> >>> 
> >>> better
> >>> 
> >>> > > bracktrace (less ??)?
> >>> > 
> >>> > Installed it.
> >>> > still I'm not able to make any sense out of it.
> >>> > 
> >>> > Updated backtrace :  http://paste.kde.org/pa8f27933/
> >>> 
> >>> How are you getting the backtrace?
> >> 
> >> I use Qt Creator, when it crashes I use create full backtrace option to
> >> get this backtrace.
> >> Further more using gdb + terminal I get
> >> this<http://paste.kde.org/p11fad1cf/>backtrace.
> >> 
> >> Can you mark in which thread the crash is
> >> 
> >>> happening?
> >> 
> >> I get an ABORT signal when TextDocumentGeneratorPrivate::createTextPage(.
> >> . .) is called inside core/textdocumentgenerator.cpp. Now inside that 99%
> >> of the times I get a crash on L81 (my branch).
> >> 
> >>> Cheers,
> >>> 
> >>>   Albert
> >>>   
> >>> > > Cheers,
> >>> > > 
> >>> > >   Albert
> >>> > >   
> >>> > > > > What has changed
> >>> > > > > since last time we tried to do this?
> >>> > > > 
> >>> > > > I have noticed that it only crashes when the epub has an adequate
> >>> 
> >>> amount
> >>> 
> >>> > > of
> >>> > > 
> >>> > > > images. Epubs with no images or 1 or 2 images are less likely to
> >>> 
> >>> crash.
> >>> 
> >>> > > The
> >>> > > 
> >>> > > > more the images the more likely it is to crash.
> >>> > > > 
> >>> > > > Now we don't have to guess if it will crash on this file or not.
> >>> > > > Considering all this, I have given you an ePub that is most likely
> >>> 
> >>> to
> >>> 
> >>> > > crash
> >>> > > 
> >>> > > > atleast once before completing a round trip (top to bottom &
> >>> 
> >>> bottom to
> >>> 
> >>> > > > top).
> >>> > > > 
> >>> > > > > Cheers,
> >>> > > > > 
> >>> > > > >   Albert
> >>> > > > >   
> >>> > > > > > So, can we please help, me get this done.
> >>> > > > > > It's the same bug that we once tried to fix on IRC.
> >>> > > > > > 
> >>> > > > > > I'll be available on #okular, same time as usual.
> >>> > > > > > 
> >>> > > > > > Cheers,
> >>> > > > > > Jaydeep
> >>> > > > > 
> >>> > > > > _______________________________________________
> >>> > > > > Okular-devel mailing list
> >>> > > > > Okular-devel at kde.org
> >>> > > > > https://mail.kde.org/mailman/listinfo/okular-devel
> >>> > > 
> >>> > > _______________________________________________
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> >>> 
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