locks cannot be interrupted on OpenBSD

[rpointel]

BPO	20564
Nosy	@vstinner
Files	interrupt_lock_acquire.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2014-02-18.08:21:18.749>
created_at = <Date 2014-02-08.18:19:44.602>
labels = ['tests']
title = 'locks cannot be interrupted on OpenBSD'
updated_at = <Date 2014-02-18.08:36:18.166>
user = 'https://bugs.python.org/rpointel'

bugs.python.org fields:

activity = <Date 2014-02-18.08:36:18.166>
actor = 'rpointel'
assignee = 'none'
closed = True
closed_date = <Date 2014-02-18.08:21:18.749>
closer = 'vstinner'
components = ['Tests']
creation = <Date 2014-02-08.18:19:44.602>
creator = 'rpointel'
dependencies = []
files = ['34054']
hgrepos = []
issue_num = 20564
keywords = []
message_count = 15.0
messages = ['210672', '210678', '210682', '210684', '210685', '210995', '210996', '211017', '211051', '211057', '211061', '211462', '211483', '211485', '211490']
nosy_count = 4.0
nosy_names = ['vstinner', 'neologix', 'python-dev', 'rpointel']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue20564'
versions = ['Python 3.3', 'Python 3.4']

[rpointel]

Hi,

I have 2 tests which "failed" on OpenBSD (tested on i386, amd64 and sparc64) in:

• test_threadsignals.py/test_lock_acquire_interruption
• test_threadsignals.py/test_rlock_acquire_interruption

======================================================================
FAIL: test_lock_acquire_interruption (main.ThreadSignals)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "Lib/test/test_threadsignals.py", line 94, in test_lock_acquire_interruption
    self.assertLess(dt, 3.0)
AssertionError: 5.020112991333008 not less than 3.0

======================================================================
FAIL: test_rlock_acquire_interruption (main.ThreadSignals)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "Lib/test/test_threadsignals.py", line 122, in test_rlock_acquire_interruption
    self.assertLess(dt, 3.0)
AssertionError: 5.0101478099823 not less than 3.0

On the 3 machines it took ~ 5sec.
I'm asking why it's 3 seconds by default in the tests? Could we modify the value to 6 instead of 3, is it acceptable?

Thanks for your response,

Remi.

[neologix]

I'm asking why it's 3 seconds by default in the tests?
Could we modify the value to 6 instead of 3, is it acceptable?

No, see this comment:
"""
self.assertRaises(KeyboardInterrupt, lock.acquire, timeout=5)
dt = time.time() - t1
# Checking that KeyboardInterrupt was raised is not sufficient.
# We want to assert that lock.acquire() was interrupted because
# of the signal, not that the signal handler was called immediately
# after timeout return of lock.acquire() (which can fool assertRaises).
"""

5s corresponds exactly to the timeout passed to acquire(), which means that it didn't get interrupted, which is precisely the goal of the test.

[rpointel]

arf, sorry for the noise... I didn't seen this.

[vstinner]

What is your OpenBSD version? Before 5.2, there were many issues with signals.

[rpointel]

I'm in -current (5.5-beta).

[neologix]

So this looks like a bug.

When running the test, is faulthandler enabled (--timeout option)?

[neologix]

So this looks like a bug.

I mean an OpenBSD bug.

[rpointel]

Thanks for your response.

When running the test, is faulthandler enabled (--timeout option)?

It seems yes:

#############################################################################################
$ PYTHONPATH=. ./python Tools/scripts/run_tests.py -j 1 -W --timeout=3600 test_threadsignals
/home/remi/dev/cpython/python -W default -bb -E -R -m test -r -w -u all,-largefile,-audio,-gui -j 1 -W --timeout=3600 test_threadsignals
Using random seed 8501335
[1/1] test_threadsignals
test_interrupted_timed_acquire (test.test_threadsignals.ThreadSignals) ... ok
test_lock_acquire_interruption (test.test_threadsignals.ThreadSignals) ... FAIL
test_lock_acquire_retries_on_intr (test.test_threadsignals.ThreadSignals) ... ok
test_rlock_acquire_interruption (test.test_threadsignals.ThreadSignals) ... FAIL
test_rlock_acquire_retries_on_intr (test.test_threadsignals.ThreadSignals) ... ok
test_signals (test.test_threadsignals.ThreadSignals) ... ok

======================================================================
FAIL: test_lock_acquire_interruption (test.test_threadsignals.ThreadSignals)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/remi/dev/cpython/Lib/test/test_threadsignals.py", line 94, in test_lock_acquire_interruption
    self.assertLess(dt, 3.0)
AssertionError: 5.019763469696045 not less than 3.0

======================================================================
FAIL: test_rlock_acquire_interruption (test.test_threadsignals.ThreadSignals)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/remi/dev/cpython/Lib/test/test_threadsignals.py", line 122, in test_rlock_acquire_interruption
    self.assertLess(dt, 3.0)
AssertionError: 5.020080804824829 not less than 3.0

---

Ran 6 tests in 13.295s

FAILED (failures=2)
test test_threadsignals failed
1 test failed:
test_threadsignals
Re-running failed tests in verbose mode
Re-running test 'test_threadsignals' in verbose mode
test_interrupted_timed_acquire (test.test_threadsignals.ThreadSignals) ... ok
test_lock_acquire_interruption (test.test_threadsignals.ThreadSignals) ... FAIL
test_lock_acquire_retries_on_intr (test.test_threadsignals.ThreadSignals) ... ok
test_rlock_acquire_interruption (test.test_threadsignals.ThreadSignals) ... FAIL
test_rlock_acquire_retries_on_intr (test.test_threadsignals.ThreadSignals) ... ok
test_signals (test.test_threadsignals.ThreadSignals) ... ok

======================================================================
FAIL: test_lock_acquire_interruption (test.test_threadsignals.ThreadSignals)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/remi/dev/cpython/Lib/test/test_threadsignals.py", line 94, in test_lock_acquire_interruption
    self.assertLess(dt, 3.0)
AssertionError: 5.019940614700317 not less than 3.0

======================================================================
FAIL: test_rlock_acquire_interruption (test.test_threadsignals.ThreadSignals)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/remi/dev/cpython/Lib/test/test_threadsignals.py", line 122, in test_rlock_acquire_interruption
    self.assertLess(dt, 3.0)
AssertionError: 5.020142078399658 not less than 3.0

---

Ran 6 tests in 13.293s

FAILED (failures=2)
test test_threadsignals failed

#############################################################################################

Do I miss a thing?

[vstinner]

To make test_lock_acquire_interruption and test_rlock_acquire_interruption more reliable, the test should maybe run a fresh Python process to get a well known number of threads. Some Python modules create C threads like Tkinter. faulthandler creates also an hiding C thread, but it is supposed to ignore all signals (it calls pthread_sigmask).

@remi: Can you please test interrupt_lock_acquire.py? It should be the same than the unit test, but in a fresh Python process.

[rpointel]

Can you please test interrupt_lock_acquire.py? It should be the same than the unit test, but in a fresh Python process.

Thanks for your response, this is what I have:

$ PYTHONPATH=. ./python ./interrupt_lock_acquire.py 
Traceback (most recent call last):
  File "./interrupt_lock_acquire.py", line 30, in <module>
    raise Exception("dt > 3: dt=%s" % dt)
Exception: dt > 3: dt=5.011708974838257

Remi.

[neologix]

Well, then it's definitely an OpenBSD bug, and we can't do anything
more than skip the test.

[vstinner]

So this looks like a bug.

Or a different design choice?

It looks like the kernel restarts the wait if it was interrupted.

"ignore interruptions other than cancelation"
http://ftp.cc.uoc.gr/mirrors/OpenBSD/src/lib/librthread/rthread_sem.c

"test that sem_timedwait() resumes after handling a signal"
http://mirrors.ircam.fr/pub/OpenBSD/src/regress/lib/libpthread/semaphore/sem_timedwait/sem_timedwait.c

POSIX says that "The sem_timedwait() function shall fail if: [EINTR] A signal interrupted this function."
http://pubs.opengroup.org/onlinepubs/009604599/functions/sem_timedwait.html

Right now, the best we can do is to skip the test on OpenBSD (maybe only on OpenBSD <= 5.4 to see if it changes later).

[python-dev]

New changeset a3d54bb04cbb by Victor Stinner in branch 'default':
Issue bpo-20564: Skip tests on lock+signals on OpenBSD
http://hg.python.org/cpython/rev/a3d54bb04cbb

[vstinner]

@remi: You may report the feature request to OpenBSD kernel if you want. Until OpenBSD implements it, the test is now skipped in Python.

[rpointel]

You may report the feature request to OpenBSD kernel if you want. Until OpenBSD implements it, the test is now skipped in Python.

Yes, it's done yet.
However, it's good to skip it until it's implemented.