avoid creating unneeded homsets when coercing

[sagetrac-mabshoff]

Burcin reported at #4639:

sage: F = GF(13)
sage: get_memory_usage()
708.02734375
sage: for _ in xrange(10000):
....:     t = F.coerce(F(234234))
....:     
sage: get_memory_usage()
728.15234375
sage: for _ in xrange(100000):
    t = F.coerce(F(234234))
....:     
sage: get_memory_usage()
932.3125
sage: for _ in xrange(100000):
    t = F.coerce(F(234234))
....:     
sage: get_memory_usage()
1136.35546875

Since the patch by RobertWB at that ticket fixes the issue Burcin reported, but not the original one I am moving it over to this ticket.

Cheers,

Michael

Apply

attachment: trac4740-cache_coerce_from_self.patch​

Depends on #14519

CC: @burcin @robertwb @simon-king-jena

Component: memleak

Author: Simon King

Reviewer: Mike Hansen

Merged: sage-5.12.beta3

Issue created by migration from https://trac.sagemath.org/ticket/4740

[sagetrac-mabshoff]

Attachment: trac_4740_coerce-leak.patch.gz

Patch by RobertWB, originally from #4639

[sagetrac-mabshoff]

comment:1

Patch by RobertWB, review by William.

Cheers,

Michael

[sagetrac-mabshoff]

comment:2

This patch causes a failure with the pickle jar:

**********************************************************************
File "/scratch/mabshoff/release-cycle/sage-3.2.2.alpha1/devel/sage/sage/structure/sage_object.pyx", line 371, in __main__.example_16
Failed example:
    sage.structure.sage_object.unpickle_all(std)###line 682:_sage_    >>> sage.structure.sage_object.unpickle_all(std)
Expected:
    doctest:...: DeprecationWarning: Your data is stored in an old format. Please use the save() function to store your data in a more recent format.
    Successfully unpickled ... objects.
    Failed to unpickle 0 objects.
Got:
    doctest:1172: DeprecationWarning: Your data is stored in an old format. Please use the save() function to store your data in a more recent format.
    ** failed:  _class__sage_rings_finite_field_morphism_FiniteFieldHomset__.sobj
    Failed:
    _class__sage_rings_finite_field_morphism_FiniteFieldHomset__.sobj
    Successfully unpickled 453 objects.
    Failed to unpickle 1 objects.
**********************************************************************
1 items had failures:
   1 of   7 in __main__.example_16

Cheers,

Michael

[sagetrac-mabshoff]

comment:3

Once the pickling issue is fixed this should go in.

Cheers,

Michael