[Cython] Acquisition counted cdef classes

[Robert Bradshaw]

On Mon, Oct 24, 2011 at 2:52 PM, mark florisson
<markflorisson88 at gmail.com> wrote:
> On 24 October 2011 22:03, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
>> mark florisson wrote:
>>>
>>> These will by default not lock for operations to allow
>>> e.g. one thread to iterate over the list and another thread to index
>>> it without lock contention and other general overhead.
>>
>> I don't think that's safe. You can't say "I'm not modifying
>> this, so I don't need to lock it" because there may be another
>> thread that *is* in the midst of modifying it.
>
> I was really thinking of the case where you instantiate it in Cython
> and then do some parallel work, in which case you're the only user.
> But you can't assume that in general.

It could be useful to assert for a chunk of code that a given object
is read-only and will not be mutated for the duration of the context
(programmer error and strange crash/data corruption if it is). E.g.

with nogil, assert_frozen(my_dict):
    a = (<CdefClass>my_dict[key]).c_attribute
    [...]

All references obtained could be borrowed. Perhaps we could even
enforce this for cdef classes (but perhaps not consistently enough,
and perhaps that would make things even more confusing). Just a
thought.

- Robert