[tkinter_.py] [Mac] Crashes with message "Segmentation fault: 11"

[cztomczak]

It often crashes with this message. With system Python it crashes about 50% of the time, with Homebrew Python it crashes 100% of the time.

This error occurs randomly during initial app loading. This issue occurs only on Mac. Below logs:

[tkinter_.py] CEF Python 56.0
[tkinter_.py] Python 2.7.5 
[tkinter_.py] Tk 8.5.9
Segmentation fault: 11

There are some issues with Tk <> CEF initializations, they are conflicting each other. Tk must be initialized before CEF otherwise there was an another error described in Issue #306.

I've tried debugging it using gdb/lldb instructions from KB however I couldn't get a meaningful stack trace. On Linux gdb can show Python stack trace with "py-bt", but I have no idea how to debug this on Mac.

[tallforasmurf]

I am walking through this under Wing IDE. It fails consistently on my system. The crash happens after the call to app.mainloop(). The window appears, then the crash, with no opportunity for user interaction. With log level set to DEBUG the following appear in the log prior to cef.Initialize():

[tkinter_.py] CEF Python 57.0
[tkinter_.py] Python 3.5.1 64bit
[tkinter_.py] Tk 8.5.9

Upon cef.Initialize() this appears,

[0725/124614.059902:ERROR:child_thread_impl.cc(762)] Request for unknown Channel-associated interface: ui::mojom::GpuMain

(which I think is a red herring). Upon the app.mainloop() call these appear:

[tkinter_.py] MainFrame.on_root_configure
[tkinter_.py] MainFrame.on_root_configure
[tkinter_.py] MainFrame.on_configure
[tkinter_.py] MainFrame.on_root_configure

then the window appears and the segfault happens.

By setting a lot of breakpoints I have verified that everything works fine up until entry to embed_browser() on line 158. The crash happens during

self.browser = cef.CreateBrowserSync(window_info,
                                         url="https://www.google.com/")

I can't debug-step into this (actually I can, but the debugger next surfaces in re.py).

[tallforasmurf]

Since the hello_world.py example does not crash, the only difference would seem to be the inclusion of "window_info" in the CreateBrowserSync call. Unfortunately window_info is an opaque object from cefWindowInfo() so I can't tell you what's in it.

However, if I delete the window_info argument from the call, the segfault does not occur.

Note that in both hello_world and tkinter_ examples, the resulting window is blank, there is no display of google.com. Is there supposed to be?

Edit: also the qt.py example works, except that it also displays no web page, here is a screen grab:

[cztomczak]

When you remove the window_info parameter then you stop embedding browser inside tkinter window, so it stops being a tkinter example and thus it doesn't crash, because CEF creates the root window itself, just like in the hello world example.

A blank window might appear when your Python does not support GUI applications, see this explanation on KB page: https://github.com/cztomczak/cefpython/blob/master/docs/Knowledge-Base.md#a-blank-window-on-maclinux

[cztomczak]

Thanks for trying to debug this. The only idea I have for this moment would be to play with various tkinter options - global options or window options. Maybe changing some property of the window or some other option would get rid of the error.

[cztomczak]

Or maybe the code that fetches window handle is not right - see Issue #308. You could try hardcoding the window handle value in the script - but first you would have to obtain such handle. On Linux you can do this using "xdotool" program, for Mac you would need to google that.

[tallforasmurf]

My motive in this is to replace QWebEngine in an app based on Python 3.5, PyQt and Qt5.9. The app already works on MacOS, Ubuntu and Windows 7, but the use of QWebEngine prevents bunding it with PyInstaller.

The local Python 3.5 is standard, located in /Library/Frameworks/Python.Framework, as normal when installed from the python.org download. The Mac system Python is at 2.7, located in /System/Library/Frameworks but is not involved in any way.

I haven't touched tkinter in years so hesitate to get into that aspect but will keep poking at this in hopes of learning something useful.