Gnats 5095: Crash loading model when starting in Geospatial View

Gnats 5095: Qt assertion failure loading model when starting in Geospatial View
Phil Weinstein, 9-12-2011, Resolved / See Gnats entry.

INITIAL ANALYSIS -- see resolution

This bug doesn't seem to manifest with trivial or small models. This sequence pretty reliably produces a crash:

Start RiverWare
Switch to the Geospatial View
Load regression test: Sim/crssTest.mdl.gz
... Qt ASSERTION FAILURE in method QGraphicsScenePrivate::_q_processDirtyItems().
- See stack trace ... method detail.
- See purify trace. Note: although the assertion failed, no memory errors were detected. Purify didn't stop execution on the assertion failure, and, in fact, RiverWare seemed to run without any problems.

This is a low-level assertion failure in Qt. Purify doesn't show any memory errors (though it does fail the assertion, but continues to run correctly).

The following September 2010 patch to Qt 4.7 (which I found with Google with "assert calledEmitUpdated") seems to be related, but it's not the whole story. The 4.6.3 code is sufficiently different that this particular fix may not be exaclty what's needed -- but the fact that this is a buggy area in Qt may be relevant. For one thing, the failing assertion in 4.6.3 (i.e. not the Qt version for which the patch is intended) is tested only when an 'updateAll' flag is 'true'. And this patch corrects a bug of incorrectly setting that flag to 'false' (when it needed to stay 'true'). So, that alone wouldn't explain why this patch would avoid the assertion failure. (Note that the number of places in Qt code referring to these two flags is small). It's very possible that Qt 4.6.4 and 4.7 have fixed the problem we are seeing -- that seems likely from the Qt 4.6.3 code I'm seeing here.

"Task" Qt-3674 -- patch info screenshot
"Task" Qt-3674 -- 4.7 patch info on qt.gitorious.org ... see text below.
Qt 4.7.x -- qgraphicsscene.cpp
Qt 4.6.3 -- qgraphicsscene.cpp
... note, there are TWO drawItems() implementations. Both clear the 'updateAll' flag (as noted in the patch). The debugger didn't break in the one which is commented as being "obsolete". It does break in the other one.

Assertion calledEmitUpdated fails in QGraphicsScene. Problem was that the 'updateAll' boolean was reset to 'false' when it really should have been unchanged. This happened when rendering the scene from outside the view's paint event (i.e. from QGraphicsView/ Scene::render). We only want to reset 'updateAll' when triggering drawItems() from QGraphicsView::paintEvent, i.e. when the 'view' pointer != 0.

Broke after commit: dda8a57c.
Task-number: QT-3674

Other notes:

I have been able to produce this assertion failure only in our DEBUG build. (Not RELEASE). It's possible that this particular type of Qt assertion isn't reported (nor is fatal) in release builds.

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