Sun Jan 20 03:38:15 PST 2013

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Hello again,

Am 20.01.2013 12:23, schrieb Thomas Freitag:
> Am 20.01.2013 10:46, schrieb Adam Reichold: Hello,
> 
> I was just testing this, trying to understand the exact 
> implications for usage of Poppler's qt4 frontend. From looking at 
> it, I can have as many threads in Page::renderToImage as I like as 
> long as I don't change the render hints while doing so. (Leaving 
> overprint aside for the moment.)
> 
> This seems to work fine, but when I search the document parallel to
> that (even using different page objects and only one thread in 
> Page::search), I am getting all sorts of error messages (but no 
> crashes) about the file being malformed. From Thomas' comment on 
> the bug report, I would infer this is a known limitation? Or
> should this work?
>> Yes, Adam, this is a known limitation at the moment. I know,
>> that the bug report with over 140 comments is bad to read, but 
>> somewhere in the middle we decided to make in a first step only 
>> the page rendering thread safe. As I left yesterday as a last 
>> comment to that bug, one of the next steps will be to make the
>> qt library completely thread safe. This is hopefully just a
>> small task, because most of tat I had done that already, so we'll
>> have it probably in the very next future.

Thanks for the fast answer! This fits to what I inferred from the
discussion on the bug report.

About overprint: Is the call to globalParams::setOverprintPreview in
Page::renderToImage a threading problem?

> So my current working assumption is: there can any number of 
> rendering threads, but all rendering has stop before something
> else is to be called.
>> Don't spend too much work waiting on all rendering threads 
>> finished. I.e. in Page::search we hopefully just need to use the 
>> thread safe version of PDFDoc::displayPage in 
>> Page::prepareTextSearch, i.e.
> 
>> parentDoc->doc->displayPage( &td, index + 1, 72, 72, rotation, 
>> false, true, false, null, null, null, null, true);
> 
>> instead of
> 
>> parentDoc->doc->displayPage( &td, index + 1, 72, 72, rotation, 
>> false, true, false );
> 
>> Cheers, Thomas

Actually, if it becomes more difficult than that, I think I could live
with two types of methods in the qt4 frontend (those that are safe to
call concurrently, and those which are not). I just switched to
protecting the Document and its children by a QReadWriteLock instead
of QMutex, i.e. locking for writing by default and for reading when
calling only safe methods (currently just rendering). So it is almost
no work to gradually allow more methods to be called in parallel.
(Code is on qpdfview's Launchpad page if you are interested.)

Thanks again for the large amount of work you put into this, Thomas!

Best regards, Adam.

> Best regards, Adam.
> 
> Am 19.01.2013 17:53, schrieb Albert Astals Cid:
>>>> El Dissabte, 19 de gener de 2013, a les 08:44:34, Albert 
>>>> Astals Cid va escriure:
>>>>> New commits: commit 
>>>>> 8eb489c355d734a72e140ce7e32470d048362499 Author: Thomas 
>>>>> Freitag <Thomas.Freitag at alfa.de> Date:   Sat Jan 19 
>>>>> 17:43:08 2013 +0100
>>>>> 
>>>>> Make rendering thread-safe
>>>>> 
>>>>> Bug #50992
>>>> This is quite a big of a change, we did lots of testing to 
>>>> make sure it did not break things, but more testing is more 
>>>> than welcome.
>>>> 
>>>> Cheers, Albert 
>>>> _______________________________________________ poppler 
>>>> mailing list poppler at lists.freedesktop.org 
>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
>>>> 
>> _______________________________________________ poppler mailing 
>> list poppler at lists.freedesktop.org 
>> http://lists.freedesktop.org/mailman/listinfo/poppler
>> 
>> .
>> 
> 
> 
> _______________________________________________ poppler mailing 
> list poppler at lists.freedesktop.org 
> http://lists.freedesktop.org/mailman/listinfo/poppler
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