I have found a little more information here that might be relevant (from
Python forums,
https://discuss.python.org/t/segfault-using-sage-function-with-try-except-alarminterrupt/16983/10),
and I'm hoping this might drum up some interest before I blindly try to
submit a bug report.
It's possible my vanilla Python code is not playing well with Sage - which
is apparently written in Cython. If someone could let me know how to
"cythonize" the follow code block, that would be helpful:
alarm(5)
try:
grpstr = str(G.structure_description())
except ValueError:
if G.simplified().relations() == ():
grpstr = "F" + str(G.simplified().ngens())
else:
grpstr = "--"
ExCases += 1
pass
except AlarmInterrupt:
grpstr = "--"
ExCases += 1
pass
except:
print("Some Unhandled exception!")
grpstr="I broke!"
pass
cancel_alarm()
On Thu, Jun 16, 2022 at 11:40 AM dus...@merrimack.edu
wrote:
> I'm getting multiple exception errors resulting in a segfault when trying
> to control how long SageMath spends on structure_description() of a finite
> group. I'll attach a MWE and traceback, but basically what I'm doing is:
>
> creating a Finite Group with ~10-20 generators and ~half that relations.
>
> Setting an alarm...
> running structure_description() with three possible outcomes of
> try...except:
> * it works, tell me the result
> * it fails, GAP knows why and I take over
> * It fails because of the alarm timeout
>
> Running this code in a loop eventually results in a segfault, probably
> with some conflict between the alarm and GAP exceptions, but the traceback
> suggests it's a problem in the free_group module...anyone have any thoughts?
>
> [running code resulting in crash]
>
> Group Type is: --
> 20 [[9, 6, 2, 8], [8, 8], [10], [7, 2, 14, 4], [8], [14, 2, 6], [2, 10],
> [7, 9, 2], [10, 6, 8, 2], [13, 6, 11, 8], [3], [3]]
> Finitely presented group < x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10,
> x11, x12, x13, x14 | x8*x5*x1*x7, x7^2, x9, x6*x1*x13*x3, x7, x13*x1*x5,
> x1*x9, x6*x8*x1, x9*x5*x7*x1, x12*x5*x10*x7, x2, x2 >
> Some Unhandled exception!
> Group Type is: --
> 21 [[5, 11, 6, 11], [1], [7, 11, 12], [14, 4], [7], [1], [10, 4], [14],
> [8, 11, 10, 1], [10, 10, 4], [10, 12], [12, 10, 14, 10]]
> Traceback (most recent call last):
> File
> "/home/cduston/Downloads/SageMath/local/lib/python3.7/site-packages/sage/groups/free_group.py",
> line 881, in _element_constructor_
> P = x.parent()
> AttributeError: 'list' object has no attribute 'parent'
>
> During handling of the above exception, another exception occurred:
>
> Traceback (most recent call last):
> File "MWE.sage.py", line 39, in
> G=H/[H(Y[i]) for i in range(g*V)]
> File "MWE.sage.py", line 39, in
> G=H/[H(Y[i]) for i in range(g*V)]
> File "sage/structure/parent.pyx", line 900, in
> sage.structure.parent.Parent.__call__
> (build/cythonized/sage/structure/parent.c:9218)
> File "sage/structure/coerce_maps.pyx", line 156, in
> sage.structure.coerce_maps.DefaultConvertMap_unique._call_
> (build/cythonized/sage/structure/coerce_maps.c:4448)
> File
> "/home/cduston/Downloads/SageMath/local/lib/python3.7/site-packages/sage/groups/free_group.py",
> line 883, in _element_constructor_
> return self.element_class(self, x, **kwds)
> File
> "/home/cduston/Downloads/SageMath/local/lib/python3.7/site-packages/sage/groups/free_group.py",
> line 230, in __init__
> AbstractWordTietzeWord = libgap.eval('AbstractWordTietzeWord')
> File "sage/libs/gap/libgap.pyx", line 400, in
> sage.libs.gap.libgap.Gap.eval (build/cythonized/sage/libs/gap/libgap.c:4205)
> File "sage/libs/gap/util.pyx", line 395, in sage.libs.gap.util.gap_eval
> (build/cythonized/sage/libs/gap/util.c:5990)
> cysignals.signals.SignalError: Segmentation fault
>
>
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> .
>
--
Christopher L Duston
Associate Professor of Physics
Director of the Merrimack Observatory
Merrimack College
Palmisano 223
dust...@merrimack.edu
(978) 837 3491
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