Message-ID: <561052DA.304@yandex.ru>
Date: Sun, 04 Oct 2015 01:12:42 +0300
From: Nikolai Zhubr <n-a-zhubr@yandex.ru>
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To: pgadmin-support@postgresql.org
Subject: Re: Repaint lockup in ctlSQLBox::OnPositionStc
 on windows (Was: SQL-panel causes 100% CPU and lockup on windows)
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Hi all,

ok, it is broken since this commit:

http://git.postgresql.org/gitweb/?p=pgadmin3.git;a=patch;h=b0ecbbca7f77c0f07cff67bba3d2bca28954a1e2

-   EVT_STC_UPDATEUI(-1,  ctlSQLBox::OnPositionStc)
+   EVT_STC_PAINTED(-1,  ctlSQLBox::OnPositionStc)

It appears that in previous version of scintilla, there existed a 
SCN_POSCHANGED event, which then got obsolete and replaced by 
SCN_UPDATEUI, and probably that is why the name 'OnPositionStc' was 
chosen for the handler. So linking OnPositionStc() to STC_UPDATEUI was 
correct and in accordance with scintilla's manual.
However the change from EVT_STC_UPDATEUI to EVT_STC_PAINTED was 
incorrect. These events are not quite equivalent. EVT_STC_PAINTED has a 
somewhat different purpose.

I've checked, reverting back to EVT_STC_UPDATEUI indeed fixed CPU load 
and lockup issues on windows. See also
http://www.scintilla.org/ScintillaDoc.html#SCN_PAINTED
http://www.scintilla.org/ScintillaDoc.html#SCN_UPDATEUI
http://www.scintilla.org/ScintillaHistory.html
http://web.mit.edu/jhawk/mnt/spo/sandbox/punya/anjuta-1.2.3/doc/ScintillaDoc.html 
  (-- this is some older document with a more detailed explanation of 
SCN_UPDATEUI)

Some relevant excerptions:

"SCN_PAINTED: is to update some _other_ widgets based on a change."

"SCN_POSCHANGED: notification is deprecated as it was causing confusion. 
Use SCN_UPDATEUI instead."

"SCN_UPDATEUI, SCN_CHECKBRACE:
Either the text or styling [...] common use is to check whether the 
caret is next to a brace and set highlights on this brace and its 
corresponding matching brace."

So for me this all sounds clear sufficiently. I'll stick with 
EVT_STC_UPDATEUI and I can rebuild it myself if I have to. Whether fix 
git respectively or not is up to maintainers now.


Thank you,
Nikolai


03.10.2015 21:56, I wrote:
> Hi all,
>
> Ok, I've verified that ctlSQLBox::OnPositionStc() is broken.
>
> If I comment the code for highlighting in it (that is, almost all of its
> body), the problem goes away.
>
> I've found quite some problems observed with it and attempted to fix
> previously, like e.g. the one from 2011:
> ---------------
> + // Ensure we don't recurse through any paint handlers
> + Freeze();
> UpdateLineNumber();
> + Thaw();
>
> // Clear all highlighting
> ---------------
> That was most probably only a partial fix, and it was subsequently
> reverted.
>
> I'd like to also note that 'OnPositionStc' name is pretty much
> misleading. If it was named 'OnPaintedStc' it would be more consistent
> and more hinting where the problem is. I'm aware that renaming alone
> don't usually fix bugs, but it might help humans better catch ones.
>
> Ok, anyway, I've got no real fix for now, but I'm going on.
>
>
> Thank you,
> Nikolai
>
>


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