AlarmInterrupt in divisors doctest in integer.pyx

[gh-mwageringel]

The following doctest for divisors() in integer.pyx raises an AlarmInterrupt on some machines (using CentOS 7.6.1810).

$ ./sage -t --long src/sage/rings/integer.pyx
Running doctests with ID 2019-07-10-22-17-10-03f99627.
Git branch: develop
Using --optional=build,dochtml,memlimit,mpir,python2,sage
Doctesting 1 file.
sage -t --long --warn-long 85.5 src/sage/rings/integer.pyx
**********************************************************************
File "src/sage/rings/integer.pyx", line 3009, in sage.rings.integer.Integer.divisors
Failed example:
    for i in range(20):  # long time
        try:
            alarm(RDF.random_element(1e-3, 0.5))
            _ = n.divisors()
            cancel_alarm()  # we never get here
        except AlarmInterrupt:
            pass
Exception raised:
    Traceback (most recent call last):
      File "/amd/compute/mwagerin/git/sage_compute/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 681, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/amd/compute/mwagerin/git/sage_compute/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 1105, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.rings.integer.Integer.divisors[20]>", line 4, in <module>
        _ = n.divisors()
      File "sage/rings/integer.pyx", line 3079, in sage.rings.integer.Integer.divisors (build/cythonized/sage/rings/integer.c:19781)
        ptr = <unsigned long*>check_allocarray(divisor_count, 3 * sizeof(unsigned long))
      File "memory.pxd", line 87, in cysignals.memory.check_allocarray (build/cythonized/sage/rings/integer.c:47091)
    MemoryError: failed to allocate 33554432 * 24 bytes
    AlarmInterrupt in doctesting framework
**********************************************************************
Tests run before doctest exception:
sage: a = Integer(3) ; b = Integer(4) ## line 11 ##

...

sage: n = -920384; n.__hash__() ## line 3586 ##
**********************************************************************
Traceback (most recent call last):
  File "/amd/compute/mwagerin/git/sage_compute/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 2487, in __call__
    doctests, extras = self._run(runner, options, results)
  File "/amd/compute/mwagerin/git/sage_compute/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 2536, in _run
    result = runner.run(test)
  File "/amd/compute/mwagerin/git/sage_compute/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 879, in run
    return self._run(test, compileflags, out)
  File "/amd/compute/mwagerin/git/sage_compute/local/lib/python2.7/site-packages/sage/doctest/forker.py", line 622, in _run
    print("sage: " + example.source[:-1] + " ## line %s ##"%(test.lineno + example.lineno + 1))
  File "src/cysignals/signals.pyx", line 320, in cysignals.signals.python_check_interrupt
AlarmInterrupt

----------------------------------------------------------------------
sage -t --long --warn-long 85.5 src/sage/rings/integer.pyx  # AlarmInterrupt in doctesting framework
----------------------------------------------------------------------

The second half of the output varies, as sometimes the AlarmInterrupt is observed during one of the subsequent doctests of the file.

[gh-mwageringel]

Ticket #26002 might be related, as the same error is mentioned there. The affected doctest was added in #8573 and is meant to check for memory leaks. Is this actually a memory leak?

[jdemeyer]

The real cause seems to be MemoryError: failed to allocate 33554432 * 24 bytes

Is this a machine with few RAM?

[gh-mwageringel]

Oh, good point. The machine has plenty of RAM, but I had not realized that this is another incarnation of #28106 where the memlimit is hit during doctests. Raising it just a bit from 3300 to 3400 makes the test pass.

This ticket can be closed as duplicate – my bad. Thank you for the help.