Common problems when debugging Deephaven
This guide describes common Deephaven-specific issues you may encounter when debugging.
The examples shown use PyCharm with pip-installed Deephaven, but these problems and solutions apply to all IDEs and installation methods.
Note
These issues are specific to how Deephaven works and are not related to your debugger setup.
Lazy evaluation of some table operations
Some Deephaven table operations like update_view utilize lazy evaluation, where the results of the operation are not computed until they are required by another downstream operation. In the absence of such downstream operations, the debugger may not hit the expected parts of the code since no real work is being done. This is particularly salient when attempting to debug user-defined functions called in lazy table operations. Take this example:
In this case, the breakpoint will not be reached, because update_view does not evaluate udf. To force evaluation for debugging purposes, use select:
Ticking tables and the main thread
Currently, Deephaven only notifies Python debuggers of its main thread. However, ticking Deephaven tables spawn new Java threads where evaluation actually happens. If the main thread is not explicitly kept alive, it will shut down before the debugger can reach operations that happen on the other thread. Again, this is particularly relevant with user-defined functions:
The main thread here shuts down before the UDF is reached. To remedy this, explicitly keep the main thread alive with a call to time.sleep:
