Clarify return value of executor.shutdown

[benclifford]

Some executors returned constant True; some returned None. No use is made of this return value, so set it to None in the base definition.

This will break any outside-of-parsl code which actually relies on a None or True being returned.

Type of change

• Code maintentance/cleanup

[khk-globus]

Meaningless return value. The function either excepted, or it returned True. I haven't delved completely in, but I don't think we're extending any interface that wants this the RV to be a boolean, so I think this change "should be good."

I do note that parsl.executors.base.ParslExecutor.__exit__ returns False:

# parsl/executors/base.py
...
    def __enter__(self) -> Self:
        return self

    def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> Literal[False]:
        self.shutdown()
        return False

... which seems to me of the same order or mindset as this PR.

[benclifford]

I don't think we're extending any interface

originally these were meant to look like executors from the concurrent module - as time has passed they've moved away from that interface enough that it's probably better to refer to them as "inspired by" now.

[benclifford]

I think that False in __exit__ has a purpose:

If an exception is supplied, and the method wishes to suppress the exception (i.e., prevent it from being propagated), it should return a true value. Otherwise, the exception will be processed normally upon exit from this method.

https://docs.python.org/3.9/reference/datamodel.html?highlight=__exit__#object.__exit__

[khk-globus]

I think that False in __exit__ has a purpose:

Right; but it's summarily returned. As I read that then, all exceptions are ignored when in that context manager, no? As in, the return True was ignored from the Executor, and I was thinking that given the co-location to self.shutdown(), the exceptions being summarily ignored might be related in thought-process (or thought-less-process, if you will).

Perhaps a different conversation than I was thinking, and not related to this PR, but I noted it while reading the codes.

[khk-globus]

Aaaaand ... I see it now. Too late and I should go to bed. NVM.