Debugging Non-Python Mainloops

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The debug process connects to the IDE using a TCP/IP socket which is serviced from the debug tracer. Since Python only calls the tracer when Python byte codes are being executed, the debug process may become unresponsive if it spends long periods of time in non-Python code, such as in a C or C++ event loop. In this case, messages from Wing, such as Pause or changes to breakpoints, will be ignored by the debug process until some Python code is run again.

This is rarely an issue in practice since most code calls Python code periodically, and Wing's debugger contains hooks that entirely avoid the problem in PyQt, Gtk, Tkinter, wxPython, and Zope.

In the rare cases where the problem does occur, simple work-arounds include: (1) Schedule some Python code to run periodically as an idle task or timeout, or (2) just don't try to Pause or change breakpoints while the debug process is busy.

An alternative is to write a plug-in that services the debugger's sockets even when no Python code is being called, as described below.

Writing Non-Python Mainloop Support

Wing provides an API for adding the hooks necessary to ensure that the debugger's network sockets are serviced at all times. In order to use this, you must be able to register the debugger's socket in your environment's mainloop, or cause your mainloop to call select() on the socket periodically and invoke a provided callback when there is activity on the socket.

Mainloop hooks are written as separate modules that are placed into src/debug/tserver in your Wing installation directory (on macOS, this is inside Contents/Resources in Wing's .app folder). This directory contains several examples that can be used as a starting point.

To add your own non-Python mainloop support, you must:

  • Copy one of the source examples, such as, to a file name where xxxx is the name of your non-Python mainloop environment.
  • Determine the names of indicator modules Wing can used to identify that this mainloop environment is being loaded and set kIndicatorModuleName.
  • Implement the _Setup(), RegisterSocket(), and UnregisterSocket() methods. Do not alter any code from the examples except the code within the methods. The name of the classes and constants at the top level of the file must remain the same.
  • Add the name of your module, minus the '.py' to the list kSupportedMainloops in

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