[yt-dev] YTSliceBase.reslice broken

[Anthony Scopatz]

I agree with Matt,

I think #4 is the cleanest.

Be Well
Anthony


On Tue, Jul 23, 2013 at 11:36 AM, Matthew Turk <matthewturk at gmail.com>wrote:

> Hi Doug,
>
> My vote is for number four.
>
> Matt
> On Jul 23, 2013 9:17 AM, "Douglas Harvey Rudd" <drudd at uchicago.edu> wrote:
>
>> Hi all,
>>
>> In writing test cases for the slice selector I discovered that the
>> reslice function of YTSliceBase appears to be broken due to caching at
>> several levels.
>>
>> 1) the selector object stores the slice coordinate and was never updated
>> 2) the grid selection is cached
>> 3) the cell mask (created by fill_mask) is only updated when the selector
>> id changes
>>
>> I fixed 1) and 2) by overloading the clear_data function in
>> YTSelectionDataContainer:
>>
>>     def clear_data(self):
>>         """
>>         Clears out all data from the YTSelectionDataContainer instance,
>> freeing memory.
>>         """
>>         self._selector = None
>>         self._current_chunk = None
>>         self.field_data.clear()
>>
>> and replaced the call to self.field_data.clear() in YTSliceBase.reslice
>> with self.clear_data()
>>
>> This forces the selector to be recreated when it is next requested.
>>  Unfortunately the problem persisted, inconsistently, and I tracked it down
>> to 3).  The id of the newly created selector was sometimes identical to the
>> one prior to the reslice command.  In the grid_patch hierarchy, the cell
>> mask is only recreated if the id of the selector object has changed, and so
>> in this case an old mask persisted.
>>
>> I see several options for solving the problem:
>>
>> 1) replace using the python id function with a random identifier or hash
>> of the actual selector data, to ensure it detects when the parameters have
>> changed
>> 2) reach into the hierarchy from the clear_data function and erase the
>> cached cell mask
>> 3) add a check in the hierarchy to detect if the chunking has changed
>> along with the selector (not sure how this could be done, but probably a
>> good idea anyway, for consistency)
>> 4) remove the reslice function and prevent selection data containers from
>> changing after creation
>>
>>
>> Thoughts?
>>
>>
>> Douglas Rudd
>> Scientific Computing Consultant
>> Research Computing Center
>> drudd at uchicago.edu
>>
>>
>>
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>>
>
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