Am 20.01.2013 12:38, schrieb Adam Reichold:
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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?
No, not really: overprintPreview is just read by the threads used in
Page::renderImage. So changing the flag during rendering wil cause
probably unpredictable results but nothing else. But probably it would
be clearer to don't do it there but in Document::setRenderHint.
Cheers,
Thomas
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 <[email protected]> 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
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