[Python-ideas] Concurrent safety?

[Mike Meyer]

On Mon, Oct 31, 2011 at 11:00 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>wrote:

> Mike Meyer wrote:
>
>> The goal here is to move from where we are to a place similar to where
>> handling files is, so that failing to properly deal with the possibility of
>> concurrent access causes an error when it happens, not at a point distant
>> in both time and space.
>>
>
> I don't think what you're suggesting would achieve this,
> though. The locking required for correctness often involves
> more than one object or more than one operation on an
> object. Consider
>
>   new_balance = balance + deposit
>   lock(balance)
>   balance = new_balance
>   unlock(balance)
>
> This wouldn't trigger any of your alarms, but it would
> still be wrong.


You're right - I chose my words poorly. As stated, solving it would involve
solving the halting problem. Replace the word "properly" with "at all".
I.e. - if you don't think about a concurrent access and should have, it'll
cause an error. If you think about it and get it wrong - well, nothing will
prevent all bugs. Partially automated resource allocation doesn't prevent
the programmer from writing bad code, and this is in that category.

    <mike
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