[Webkit-unassigned] [Bug 230257] [GTK][a11y] Add implementation of component interface when building with ATSPI

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=230257

--- Comment #8 from Andres Gonzalez <andresg_22 at apple.com> ---
(In reply to Andres Gonzalez from comment #7)
> (In reply to Carlos Garcia Campos from comment #6)
> > (In reply to Andres Gonzalez from comment #5)
> > > (In reply to Carlos Garcia Campos from comment #4)
> > > > (In reply to Andres Gonzalez from comment #3)
> > > > > (In reply to Carlos Garcia Campos from comment #1)
> > > > > > Created attachment 440592 [details]
> > > > > > Patch
> > > > > 
> > > > > --- a/Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.h
> > > > > +++ a/Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.h
> > > > > 
> > > > > +    RefPtr<AXIsolatedObject> nodeForID(AXID) const;
> > > > > 
> > > > > nodeForID belongs to the tree not to the isolated object. I think it is a
> > > > > better design to keep it in AXIsolatedTree. Do you have a reason to move it
> > > > > to AXIsolatedObject?
> > > > 
> > > > Yes, I need it in AccessibilityObjectAtspi::hitTest() only because of WTR
> > > > actually. Since WTR calls accessibility api from the web process main
> > > > thread, I can't use AXIsolatedObject::accessibilityHitTest() because it's
> > > > always expected to be called from the secondary thread (nodeForID only works
> > > > from the a11y thread). I can't use callOnAXthreadAndWait, because first
> > > > thing AXIsolatedObject::accessibilityHitTest() is
> > > > retrieveValueFromMainThread() but main thread is blocked. So, I split it
> > > > adding AccessibilityObjectAtspi::objectAtPoint() that is always called by
> > > > the main thread and does the coordinate conversion + accessibilityHitTest().
> > > > When called from the main thread (WTR only) it's called directly and the
> > > > wrapper object returned. When called from the AX thread I need the
> > > > nodeForID() call to get the wrapper from the isolated object. 
> > > 
> > > Can't you get the wrapper from the isolated object? AXCoreObject::wrapper()
> > > should work in all objects, isolated or live.
> > 
> > hmm, I'm not sure it's ok to get the wrapper from the main thread, I assumed
> > that AXIsolatedObject::accessibilityHitTest() returned the AXID because it's
> > safe to send the id from main to AX thread, but not the wrapper?
> 
> Let's go back for a moment to the origin of the problem. As you said, you
> couldn't use AccessibilityController::executeOnAXThreadAndWait for HitTest
> because HitTest  will dispatch back to the main thread that it would be
> waiting, resulting in deadlock. The way we worked around this was by:
> 
> AccessibilityController::executeOnAXThreadAndWait calls
> AXThread::dispatch that in turn calls
> axThread.wakeUpRunLoop
> 
> On Mac wakeUpRunLoop does
> 
> void AXThread::wakeUpRunLoop()
> {
>     CFRunLoopSourceSignal(m_threadRunLoopSource.get());
>     CFRunLoopWakeUp(m_threadRunLoop.get());
> }
> 
> But it is a no-op in GTK. Could we try something equivalent in GTK?

The issue is not unique to HitTest, but you would have the same problem for any call into the API that needs to dispatch to the main thread. So we need to find a general solution.

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