[Python-ideas] fork

[Sven R. Kunze]

Hi everybody,

I finally managed to implement all the tiny little details of fork that were important from my perspective (cf. https://pypi.python.org/pypi/xfork).

An interesting piece of code is the iterative evaluation of OperationFuture using generators to avoid stack overflows.

The only thing I am not satisfied with is exception handling. In spite of preserving the original traceback, when the ResultEvaluationError is thrown is unfortunately up to the evalutor. Maybe, somebody here has a better idea or compromise here.

Co-workers proposed using function scopes as the ultimate evaluation scope. That is when a function returns a ResultProxy, it gets evaluated. However, I have absolutely no idea how to do this as I couldn't find any __returned__ hook or something.

I learned from writing this module and some key insights I would like to share:

1) Pickle not working with decorated functions

2) One 'traceback' is not like another. There are different concepts in Python with the same name.

3) Tracebacks are not really first-class, thus customizing them is hard/impossible.

4) contextlib.contextmanager only creates decorators/context managers with parameters but what if you have none? @decorator() looks weird.

5) Generators can be used for operation evaluation to avoid the stack limit

6) Python is awesome: despite the above obstacles, I managed to hammer out a short and comprehensible implementation for fork.

It would be great if experts here could fix 1) - 4). 1) - 3) have corresponding StackOverflow threads.

@_Andrew_
I am going to address you questions shortly after this.

Best,
Sven

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