IPEP 19: concurrent.futures (PEP 3148) for IPython.parallel

Status	Active
Author	Min RK <benjaminrk@gmail.com>
Created	June 28, 2013
Updated	June 28, 2013

There are two pieces to PEP 3148:

• Executors
• Futures

In IPython, the analogs to these are Views and AsyncResults. We should provide compatibility with these interfaces, as they are quite small, and we already provide most of the functionality.

3148 APIs

Future

• cancel() - we call this abort(), but this adds True/False return values.
• cancelled() - Return True if the call was successfully cancelled.
• running() - Return True if the call is currently being executed and cannot be cancelled.
• done() - We call this ready().
• result(timeout=None) - We call this get.
• exception(timeout=None) - returns Exception object (currently stored inAsyncResult._exception).
• add_done_callback(fn) - add a callback to fire on the Future. This is the only real addition of functionality.

The only real new functionality is callbacks, and the only compatibility issue is that we already have result as a property.

Executor

• submit(f, *args, **kwargs) - we call this apply.
• map(f, *iterables, timeout=None) - we have map, but don't have a mechanism for timeout.
• shutdown(wait=True) - we have shutdown, but not wait.

Implementation(s)

There are two logical choices for making these implementations:

1. Provide these APIs on the View
2. Provide separate Executor / Future classes, which wrap our implementation

Choice 1. has the advantage of not forking our interface, but there may be complications with subclassing, as concurrent.futures is not in the stdlib for Python 2. There would also be redundant method names, as many

Choice 2. may be cleaner, in that it can simply raise if concurrent.futures is not available, and always use simple subclasses. This would probably be provided as:

executor = client.executor(targets=[...])
# or
executor = view.executor

and possibly adding (there may be complications preventing this)

future = asyncresult.as_future()

but choice 2. would probably mean trading the extra metadata / multiplexing APIs for compatibility.