Debugging Multi-threaded Code

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Wing's can debug multi-threaded code, as well as single-threaded code. When a debug process has multiple threads, a thread selector popup is added to the stack selector area at the top of the various debugger tools.

By default, Wing debugs all threads in a debug process, and will stop all threads immediately if a single thread stops. Even though Wing tries to stop all threads, some may continue running if they do not enter any Python code. In that case, the thread selector will list the thread as running. It also indicates which thread was the first one to stop.

When moving among threads in a multi-threaded program, the Show Position icon that is shown in the toolbar during debugging offers a convenient way to return to the original thread and stopping position.

Whenever debugging threaded code, please note that the debugger's actions may alter the order and duration that threads are run. This is a result of the small added overhead, which may influence timing, and the fact that the debugger communicates with the IDE through a TCP/IP connection.

Selecting Threads to Debug

To avoid stopping all threads in the debugger, you must launch the debug process from outside Wing, import wingdbstub to initiate debug, and then use the debugger API's SetDebugThreads() call to specify which threads to debug. All other threads will be entirely ignored. This is documented in Debugging Externally Launched Code and the API is described in Debugger API

Note, however, that specifying a subset of threads to debug may cause problems in some code. For example, if a non-debugged thread starts running and does not return control to any other threads, then the debug process will cease to respond to the IDE. This is unavoidable since there is no way to preemptively force the debug-enabled threads to run again.