Status Bar Show Message

[JimmXinu]

My plugins use self.gui.status_bar.show_message(msg) in a number of places to indicate what's going on without throwing up a dialog. Things like "Fetching email..." and "Get stuff from web page..." and frequently a matching "Finished Fetching whatever" message when it's done, with a timeout of a few seconds.

I know that all worked when I put them in--and I admit that was a long time ago.

I've noticed more recently that the 'Finished' messages appear, but not the 'Fetching' messages.

Experimentation indicates that status_bar.show_message() calls don't update the GUI until my action/function returns back to Qt/Calibre. If I turn on notifications, I do get all the messages there.

So I suspect that Qt is not updating the status_bar widget until the GUI thread gets back to it's control.

I can brute-force it by calling status_bar.repaint() in my code, or adding a repaint call in src/calibre/gui2/init.py:237. (In both cases, the timeout isn't honored anymore.)

Kovid, would you accept a PR add repaint() like that? Is there a better fix?

FYI, I'm using Cal 8.4 on Win10.

[kovidgoyal]

I'm surprised this ever worked. In Qt the "correct" way to update the UI while also busy looping in the GUI thread is to periodically call QApplication.processEvents(ExcludeUserInputEvents)

You can do that after every call to update the status bar. Repainting it directly should also work provided you are careful to ensure no recursion occurs. I wont accept a PR to have show_message() repaint directly because this is dangeroud, if a user of show_message() happens to call it froma paintEvent, it can lead to infinite recursion and a crash.

[JimmXinu]

Originally Posted by kovidgoyal

I'm surprised this ever worked. In Qt the "correct" way to update the UI while also busy looping in the GUI thread is to periodically call QApplication.processEvents(ExcludeUserInputEvents)

You can do that after every call to update the status bar. Repainting it directly should also work provided you are careful to ensure no recursion occurs. I wont accept a PR to have show_message() repaint directly because this is dangeroud, if a user of show_message() happens to call it froma paintEvent, it can lead to infinite recursion and a crash.

Thanks. I figured there was probably a better way, but I didn't know what it was.

For the record, this appears to work from Calibre 2.85.1 forward:

from PyQt5.Qt import (QApplication, QEventLoop)
#...
    self.gui.status_bar.show_message('message')
    QApplication.processEvents(QEventLoop.ProcessEventsFlag.ExcludeUserInputEvents)

timeout param still doesn't work, but since to whole point (for me) is "Doing" ... "Done", that's fine.

BTW, I went back and checked--it definitely worked in 2.85.1.