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Problem with RenderPageToStream
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aderg View Drop Down
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    Posted: 03 Apr 20 at 11:00AM
I use RenderPageToStream in the background thread to create page preview. A separate object TQuickPDF is created in the thread.  But if there are several pictures on the page, sometimes not all pictures are displayed. How can this problem be solved?
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Ingo View Drop Down
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Joined: 29 Oct 05
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Points: 3530 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Ingo Quote  Post ReplyReply Direct Link To This Post Posted: 03 Apr 20 at 11:21AM
Hi,

but both objects points to the same file?
I don't have much experiences regarding issues like this but as far as i know at least in the past QuickPDF wasn't really threadsave?
Perhaps someone other can advice you a bit deeper...

But anyway... Cheers and welcome here for now,
Ingo
Cheers,
Ingo
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aderg View Drop Down
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Points: 11 		Post Options Post Options   Thanks (0) Thanks(0)   Quote aderg Quote  Post ReplyReply Direct Link To This Post Posted: 03 Apr 20 at 11:38AM
Yes, both objects point to the same file. Thanks, I'll try to make a copy of the file
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aderg View Drop Down
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Points: 11 		Post Options Post Options   Thanks (0) Thanks(0)   Quote aderg Quote  Post ReplyReply Direct Link To This Post Posted: 03 Apr 20 at 12:23PM
I tried making a copy of the file using SaveToStream/LoadFromStream - same problem.. ((
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Ingo View Drop Down
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...wasn't really threadsave...
Cheers,
Ingo
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tfrost View Drop Down
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Points: 437 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tfrost Quote  Post ReplyReply Direct Link To This Post Posted: 03 Apr 20 at 5:46PM
I find QPDF to be thread-safe for our purposes (rendering PDFs to bitmap).  It's the optional PDFIUM DLL that is more likely to fail with multiple threads.

If you suspect a threading issue it might be worth running Sysinternals Process Monitor and filtering on some of your image files that fail to show.  It would indicate any failure to open a file and tell you whether the reason was a sharing violation.
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Originally posted by tfrost tfrost wrote:

If you suspect a threading issue it might be worth running Sysinternals Process Monitor and filtering on some of your image files that fail to show.  It would indicate any failure to open a file and tell you whether the reason was a sharing violation.

The problem is not with different files, but with different pages of the same file. And only when using the background thread, if you do in the main thread, it is ok
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aderg View Drop Down
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Points: 11 		Post Options Post Options   Thanks (0) Thanks(0)   Quote aderg Quote  Post ReplyReply Direct Link To This Post Posted: 04 Apr 20 at 12:23AM
"Debenu Quick PDF Library can be used in a multi-threaded environment so long as a separate instance of the library is created by each thread"
 
I developed a test application. In the background stream, previews are created, but some images on the pages are sometimes skipped. Screenshot here http://yadi.sk/i/JdZlZ5-4gd341g

You can look at the source code, maybe you can tell me something
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Ingo View Drop Down
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Points: 3530 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Ingo Quote  Post ReplyReply Direct Link To This Post Posted: 05 Apr 20 at 10:23PM
This won't work:

procedure TfrmMain.btOpenClick(Sender: TObject);
begin
  if OpenDialog1.Execute(Handle) then
  begin
    LoadPDF(OpenDialog1.FileName);
    LoadPDF2(OpenDialog1.FileName);
  end;
end;

Please don't forget that this is a user-forum - not a helping forum from the publishers ;-)
Cheers,
Ingo
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Points: 11 		Post Options Post Options   Thanks (0) Thanks(0)   Quote aderg Quote  Post ReplyReply Direct Link To This Post Posted: 06 Apr 20 at 7:16AM
I solved the problem using DPLR renderer and RenderPageToDC
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