Message loop work hangs in wxPython / Qt examples on Mac. Fixed in examples. Needs further debugging in next releases.

[cztomczak]

These examples freeze during initial loading or later when typing something on a page. Issues occurs in v66.0 on Mac 10.9.

Temporary solution
See Migration Guide doc "v66+ Changes to Mac apps that integrate into existing message loop (Qt, wxPython)":
https://github.com/cztomczak/cefpython/blob/master/docs/Migration-guide.md#v66-changes-to-mac-apps-that-integrate-into-existing-message-loop-qt-wxpython

Reported problem on the CEF Forum in many details:
https://magpcss.org/ceforum/viewtopic.php?f=6&t=16181

I can see ERROR:gpu_process_transport_factory.cc(1017)] Lost UI shared context error message in console, however this message doesn't seem to be the cause, as I also see this message when running hello_world.py example and it works fine.

The Lost UI shared context error can be safely ignored according to:
https://stackoverflow.com/questions/49094399/chromedriver-showing-lost-ui-shared-context

hello_world.py, screenshot.py and tutorial.py examples do work fine on Mac.

I can also see ERROR:command_buffer_proxy_impl.cc(133)] ContextResult::kTransientFailure: Failed to send GpuChannelMsg_CreateCommandBuffer.

Passing disable-gpu and disable-gpu-compositing switches to cef.Initialize does not help. However it seems that the ContextResult::kTransientFailure.. error message disappears after these switches are passed (though more testing needed if it's just luck).

Issue is not related to recent Cython dupate, as I've tested both 0.25.2 and 0.28.4 and the issue occurs in both.

TODO: Compare cefpython/src/subprocess/main_message_loop* files with cef/tests/shared/browser/main_message_loop* files. These files may have been changed after v66 update.

[cztomczak]

Examples qt.py and wxpython.py fixed in rev b20c79b by enabling external message pump. This is just a temporary solution that combines two different approaches of integrating message loop at the same time: 1. Do message loop work in a timer 2. Enable external message pump. A correct approach is to do only one of these and not both at the same time.

[cztomczak]

Migration Guide document was updated.

[cztomczak]

Further debugging of the issue:

• See CefAppProtocol implemented in cefsimple/cefclient:
  https://github.com/chromiumembedded/cef/search?q=cefappprotocol&unscoped_q=cefappprotocol
• See JCEFApplication implementation in java-cef project:
  https://bitbucket.org/chromiumembedded/java-cef/src/master/native/util_mac.mm?fileviewer=file-view-default
• See CefAppProtocol initially implemented by cefpython. There were some issues though, so
  it might be that this wasn't implemented properly.
  Mouse context menu and <select> control crash app on Mac #156 (comment)
• See "util_mac.mm" for CEFPythonApplication implementation:
  https://github.com/cztomczak/cefpython/blob/master/src/client_handler/util_mac.mm#L18
• MacInitialize is called in cef.Initialize:
  

  cefpython/src/cefpython.pyx

  Line 502 in 4e77c93

  # Mac initialization. Need to call NSApplication.sharedApplication()