Instantiate error for each future.set_exception

[Artimi]

This fixes #246 . I've found that set_exceptions is used also in MessageBatch.failure() but it is settings an exception that is passed as argument. I would need to change it's interface to pass some function that returns the exception so it can be called for every future in MessageBatch._msg_future. Do you agree or do you have another idea?

[tvoinarovskyi]

Sorry for the long wait on this, still checking if there's a more general way of fixing it.

[Artimi]

@tvoinarovskyi Have you found something? I was trying to find this bug directly in Python but with no success. This issue is a time bomb for us because it can effectively kill one of our service. What if we use copy.deepcopy in MessageBatch?

[Artimi]

@tvoinarovskyi I added the version with copy. Now it could be ready to merge if you agrees.

[tvoinarovskyi]

Seems like copy.copy() is enough to prevent traceback changes. The tracebacks are immutable and linked in a linked list, so copy is enough.
For example:

import copy


def test_raise_many():
    err = ValueError()
    for i in range(100):
        try:
            raise copy.copy(err)
        except Exception:
            pass
    raise err

test_raise_many()

[tvoinarovskyi]

See https://gitter.im/aio-libs/Lobby?at=5a0d094871ad3f8736edbd5b reply on gitter also

[tvoinarovskyi]

Sorry, was away for some time. Please use copy and lets merge it.

[Artimi]

@tvoinarovskyi Done. Thanks for investigation.