[Octave-bug-tracker] [bug #55225] building doc figures in .eps or .pdf format occasionally silently fails

[Pantxo Diribarne]

Follow-up Comment #58, bug #55225 (project octave):

If this is the first deadlock in a while and it happens in the middle of a
test which creates graphics objects ... then I would be astonished if it was
not provoked by the changes in  cset a379987a74b0. 

Another way to have a deadlock (apart from the one in comment #56) is if we
use a BlockingQueuedConnection to execute a slot in the same thread as the
signal [1].

When initializing the qt_graphics_toolkit (in graphics-init.cc) we use
QObject::moveToThread to force the thread affinity of the qt_graphics_toolkit,
but we don't check it has taken effect at the time we initialize our first
Object.

>From Qt's doc on QObject::moveToThread [1]:

>> A QEvent::ThreadChange event is sent to this object just before the thread
affinity is changed.
 
The attached cset makes sure a deadlock due to wrong thread affinity cannot
happen, but doesn't fix the fact that the qt_graphics_toolkit may not be ready
(attached to the GUI thread) when the first object initialization is
requested.


[1] https://doc.qt.io/qt-5/qt.html#ConnectionType-enum
[2] https://doc.qt.io/qt-5/qobject.html#moveToThread

(file #49222)
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Additional Item Attachment:

File name: bug55225-4.patch               Size:3 KB
    <https://savannah.gnu.org/file/bug55225-4.patch?file_id=49222>



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