QMetaObject::invokeMethod with Qt::BlockingQueuedConnection from render thread
I have a
QQuickFramebufferObjectwhere I would like to call an external rendering function (written in Julia). Because Julia is not thread-safe, the rendering function must be called from the main thread. The easiest solution is to just set
basic, but that is easy to forget and sub-optimal for other components in the scene graph.
Looking at the scene graph documentation, I thought it would have been possible to call back into the main thread using
QQuickFramebufferObject::Renderer::render, but this seems to result in a deadlock. Using just a
Qt::QueuedConnectiondoesn't work either, because then the rendering function gets called after the context is invalidated.
It seems that the GUI thread does not continue processing events until
QQuickFramebufferObject::Renderer::renderhas completed, even though the docs state that the GUI thread is unblocked during render? The documentation for
QQuickFramebufferObjecteven states: "Using queued connections or events for communication between item and renderer is also possible".
I have added a stand-alone test case here:
The problem is at line 18 in fborender.cpp:
Is the use of a
Qt::BlockingQueuedConnectionsomehow disallowed here?