I've been meaning to fix this for over 6 years, and just kept
forgetting.
Previously ILuaContext.executeMainThreadTask worked by running
ILuaContext.issueMainThreadTask, pulling task_complete events, and then
returning the results.
While this makes the implementation simple, it means that the task's
results were converted into Lua values (in order to queue the event) and
then back into Java ones (when the event was pulled), before eventually
being converted into Lua once more.
Not only is this inefficient, as roundtripping isn't lossless, you
couldn't return functions or rich objects from main thread functions
(see https://github.com/dan200/ComputerCraft/issues/125).
We now store the return value on the Java side and then return that when
the receiving the task_complete event - the event no longer carries the
result. Note this does not affect methods using issueMainThreadTask!
e7fe22d4f8