I ran into a rather strange problem concerning pari and threading. After
my signature is a small working and a small non-working example giving
context, and here is a minimal non-working example:
sage: import threading
sage: t = threading.Thread(target=pari.version)
sage: t.start()
Exception in thread Thread-1 (version):
Traceback (most recent call last):
File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
sage: self.run()
File "/usr/lib/python3.12/threading.py", line 1010, in run
self._target(*self._args, **self._kwargs)
File "cypari2/pari_instance.pyx", line 759, in
cypari2.pari_instance.Pari.version
File "cypari2/auto_instance.pxi", line 39540, in
cypari2.pari_instance.Pari_auto.version
cysignals.signals.SignalError: Segmentation fault
I found https://github.com/sagemath/sage/issues/28800, which seems to say
that this is an issue, with the caveat that I don't know anything about
threading. I did not write the code responsible for threading in the
application I'm working on (FindStat), but it seems that threading is
somewhat unavoidable, since it uses waitress to serve. So, I have two
questions:
1) is the issue linked above indeed the reason for the segfault I am
observing?
2) is there a workaround?
Concerning 2, in case it helps: all code in FindStat accessing any
"mathematical" functionality is isolated (in fact, because it is
user-contributed). Unfortunately, I don't really understand how the
threads in FindStat are started.
Also concerning 2, ChatGPT suggested to replace waitress using gunicorn.
However, this comes with its own problems, because there is a lot of
dynamic data which must be shared, and access to which must be fast.
Many thanks and best wishes,
Martin
# Example for context
sage: import threading
sage: fun = lambda: print(BinaryTrees(3).cardinality())
sage: t = threading.Thread(target=fun)
sage: t.start()
5
sage: fun = lambda: print(RootedTrees(3).cardinality())
sage: t = threading.Thread(target=fun)
sage: t.start()
sage: Exception in thread Thread-3 (<lambda>):
Traceback (most recent call last):
File "sage/misc/cachefunc.pyx", line 1019, in
sage.misc.cachefunc.CachedFunction.__call__
KeyError: ((3,), ())
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
self.run()
File "/usr/lib/python3.12/threading.py", line 1010, in run
self._target(*self._args, **self._kwargs)
File "<ipython-input-16-3e6183557abd>", line 1, in <lambda>
File "/home/martin/sage/src/sage/combinat/rooted_tree.py", line 737, in
cardinality
return number_of_rooted_trees(self._n)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "sage/misc/cachefunc.pyx", line 1024, in
sage.misc.cachefunc.CachedFunction.__call__
File "/home/martin/sage/src/sage/combinat/rooted_tree.py", line 53, in
number_of_rooted_trees
return sum(sum(d * number_of_rooted_trees(d) for d in k.divisors()) *
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/martin/sage/src/sage/combinat/rooted_tree.py", line 53, in
<genexpr>
return sum(sum(d * number_of_rooted_trees(d) for d in k.divisors()) *
^^^^^^^^^^^^
File "sage/rings/integer.pyx", line 3184, in
sage.rings.integer.Integer.divisors
return pari_divisors_small(self)
File "sage/libs/pari/convert_sage.pyx", line 431, in
sage.libs.pari.convert_sage.pari_divisors_small
File "sage/libs/pari/convert_sage.pyx", line 468, in
sage.libs.pari.convert_sage.pari_divisors_small
cysignals.signals.SignalError: Segmentation fault
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