Well, I don't have much to add, I am mostly out of sync with recent
developments.
If the patch works and does not encounter massive performance loss it should be
ok to include it.
In terms of performance is it useful to use PDL methods as part of some cloning
ops, e.g. ->copy?
Christian
On 24/03/2011, at 2:56 AM, Chris Marshall wrote:
> On 3/23/2011 8:59 AM, Chad Davis wrote:
>> This seems to be a bug, but I'm hoping that someone that understand
>> Storable better than I can shed some light on this. I checked the list
>> archives and didn't find any discussions on this specific issue.
>>
>> I use Storable, which is implemented for piddles with
>> PDL::IO::Storable, to serialize to files. I also use Storable::dclone
>> in certain algorithms that need to clone data structures that
>> (sometimes) contain piddles. dclone (deep clone) fails to make a deep
>> clone of piddles, though. This breaks the documented semantics of
>> Storable, that dclone(.) == thaw(freeze(.))
>
>
> I took a look at the Storable documentation and came across
> this:
>
>> Any class may define hooks that will be called during the serialization
>> and deserialization process on objects that are instances of that
>> class. Those hooks can redefine the way serialization is performed
>> (and therefore, how the symmetrical deserialization should be
>> conducted).
>>
>> Since we said earlier:
>>
>> dclone(.) = thaw(freeze(.))
>>
>> everything we say about hooks should also hold for deep cloning.
>> However, hooks get to know whether the operation is a mere
>> serialization, or a cloning.
>>
>> Therefore, when serializing hooks are involved,
>>
>> dclone(.) <> thaw(freeze(.))
>>
>> Well, you could keep them in sync, but there's no guarantee it will
>> always hold on classes somebody else wrote. Besides, there is little
>> to gain in doing so: a serializing hook could keep only one attribute
>> of an object, which is probably not what should happen during a deep
>> cloning of that same object.
>
> so it appears that keeping the identity is not required
> but would seem to obey the principle of lease surprise.
> It seems like applying this patch would be reasonable
> but I'd like to hear any other thoughts (Christian?).
>
> --Chris
>
>> I tested this on the development release just announced
>> (PDL-2.4.7_013), by adding a couple tests to ./t/storable.t (patch
>> attached), like this:
>>
>>
>> # Test that freeze + thaw results in new object
>> $seq1 = sequence(3);
>> $seq1_tf = thaw(freeze($seq1));
>> $seq1->slice('1') .= 9;
>> ok(! all($seq1 == $seq1_tf), 'Initialization from seraialized object') or
>> diag($seq1, $seq1_tf);
>>
>> # Test that dclone results in a new object
>> # i.e. that dclone(.) == thaw(freeze(.))
>> $seq2 = sequence(4);
>> $seq2_dc = Storable::dclone($seq2);
>> $seq2->slice('2') .= 8;
>> ok(! all($seq2 == $seq2_dc), 'Initialization from dclone object') or
>> diag($seq2, $seq2_dc);
>>
>>
>> The first test thaw(freeze(.)) passes, but the dclone(.) test does
>> not. This is because PDL::IO::Storable has a 'return if $cloning' both
>> in STORABLE_freeze() and STORABLE_thaw(). Presumably, this is where
>> I'm looking for some feedback, this is to allow Perl to do it's own
>> (efficient) cloning, rather than serialize and deserialize potentially
>> large objects. This doesn't work for piddles, though. It just results
>> in the Perl data structure being cloned, while the underlying piddle
>> data points to the original memory. I.e. modifying the clone then
>> modifies the original. Since $cloning is not 'true' during a
>> serialization, I removed the 'return if $cloning' from both functions
>> (patch attached). This doesn't, I believe, change standard
>> serialization or deserialization, but it does make cloning via dclone
>> possible. Of course, there are probably more efficient ways of cloning
>> a piddle, but it does now conform to the Storable inferface. I
>> verified that all tests still pass with this patch. (I didn't compile
>> with PDL::FFTW or Proj4 however).
>>
>> I've been using this modified PDL::IO::Storable successfully for quite
>> a while, but wanted to mention it finally, having seen the
>> announcements of the new dev release.
>>
>> Cheers,
>> Chad
--
Christian Soeller PhD Dept. of Physiology +64 9 3737599 x82770
University of Auckland Auckland, New Zealand fax +64 9 3737499
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