[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[STINNER Victor]

STINNER Victor added the comment:

Hum, the resolution is already set to Fixed, and I didn't see this bug last 
months on buildbots, so I consider that yes, it's fixed.

Sorry Martin, I lost track of this issue and so I don't know what to do with 
your patch :-/ I will just close the issue.

--
stage: patch review -> resolved
status: open -> closed

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[Martin Panter]

Martin Panter added the comment:

Here is a patch with my suggestion to send the signal only when read() returns, 
and also closing the read end of the pipe before the write end.

--
keywords: +patch
stage:  -> patch review
Added file: http://bugs.python.org/file43147/int-write.patch

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[Martin Panter]

Martin Panter added the comment:

Found the same hang on the 3.6 branch, which was definitely running separate 
processes:

http://buildbot.python.org/all/builders/AMD64%20FreeBSD%209.x%203.x/builds/4210/steps/test/logs/stdio
== CPython 3.6.0a0 (default:ed6345cb08ab, Apr 29 2016, 18:35:36) [GCC 4.2.1 
20070831 patched [FreeBSD]]
Run tests in parallel using 4 child processes

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[Martin Panter]

Martin Panter added the comment:

Thanks, that is a very good point about threads. I remember that testing 
tkinter leaves an internal TK or TCL thread running in the background. And I 
understand Free BSD delivers process signals to arbitrary threads (not 
necessarily the main thread).

But the FreeBSD 3.5 buildbot looks like it ran test_io in a separate process 
(-j4 specified). Anyway it is another possible explanation of the hang (signal 
delivered to wrong thread, so write() call not interrupted).

Perhaps it is better to use signal.pthread_kill() instead of os.kill() in my 
proposal.

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[STINNER Victor]

STINNER Victor added the comment:

I also modified Python 3.6 to run each test file in a fresh process to avoid 
leaking too much things between tests, to isolate them better.

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[STINNER Victor]

STINNER Victor added the comment:

When we talk about signals, we must always be careful of threads. Python unit 
tests are known (at least by me ;-)) to "leak" threads. IMO the first step to 
make the test more reliable is to start it in a fresh process to control 
exactly the number of threads.

A fresh process avoids also to inherit an expected signal and/or signal handler.

I modified test_eintr recently to do something similar.

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[Martin Panter]

Martin Panter added the comment:

This recently hung AMD64 FreeBSD 9.x 3.5. The stack trace was different, and 
there is only one thread:

http://buildbot.python.org/all/builders/AMD64%20FreeBSD%209.x%203.5/builds/828/steps/test/logs/stdio
[398/398] test_io
Timeout (0:15:00)!
Thread 0x000801807400 (most recent call first):
  File 
"/usr/home/buildbot/python/3.5.koobs-freebsd9/build/Lib/unittest/case.py", line 
176 in handle
  File 
"/usr/home/buildbot/python/3.5.koobs-freebsd9/build/Lib/unittest/case.py", line 
727 in assertRaises
  File 
"/usr/home/buildbot/python/3.5.koobs-freebsd9/build/Lib/test/test_io.py", line 
3714 in check_interrupted_write
  File 
"/usr/home/buildbot/python/3.5.koobs-freebsd9/build/Lib/test/test_io.py", line 
3743 in test_interrupted_write_text

Also, x86 Ubuntu Shared 2.7 hung, but the only information I have is it was 
running test_io.

In my Free BSD case, the write() call is stuck, but in Victor’s original case, 
the background read() call is stuck. I could explain both cases as a race 
condition with the alarm signal being delivered:

Victor’s case: SIGALRM delivered somewhere inside assertRaises(), but before 
the write() system call, and Python has a chance to call the Python signal 
handler. No data is ever written, so the background read() hangs.

My case: SIGALRM delivered just before or as write() starts, so Python has no 
chance to interrupt the system call and call its own Python handler.

I wonder if we can change the test to only deliver a signal after first reading 
one byte, i.e. send the signal directly from the background thread. I think 
that should cover 99% of cases, though in theory it is possible for something 
else to interrupt write(), and our signal to be delivered while write() was 
restarting, causing it to hang. But the combination of those two events would 
be so unlikely it may not be worth worrying about.

Also, if you close the read end of the pipe before the write end, it should 
protect against flush() hanging without the EBADF hack by raising EPIPE instead.

I suggest rewriting the background thread like:

def _read():
s = os.read(r, 1)
read_results.append(s)
# The main thread is very likely to be inside the write() syscall now, so 
interrupt it
os.kill(os.getpid(), SIGALRM)

and cleaning up the pipe like:

finally:
os.close(r)
try:
wio.close()
except BrokenPipeError:
pass

--
nosy: +martin.panter
status: closed -> open
versions: +Python 2.7, Python 3.6 -Python 3.4

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[STINNER Victor]

STINNER Victor added the comment:

The test now pass on the buildbot FreeBSD 7.2.

--
resolution:  - fixed
status: open - closed

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[STINNER Victor]

New submission from STINNER Victor:

http://buildbot.python.org/all/builders/x86%20FreeBSD%207.2%203.4/builds/332/steps/test/logs/stdio

Log:
---
[157/389/1] test_io
Timeout (1:00:00)!
Thread 0x2a4f0790 (most recent call first):
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/test_io.py, 
line 3257 in _read
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/threading.py, 
line 869 in run
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/threading.py, 
line 921 in _bootstrap_inner
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/threading.py, 
line 889 in _bootstrap

Thread 0x28401040 (most recent call first):
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/threading.py, 
line 1077 in _wait_for_tstate_lock
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/threading.py, 
line 1061 in join
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/test_io.py, 
line 3278 in check_interrupted_write
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/test_io.py, 
line 3302 in test_interrupted_write_text
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/case.py, line 
577 in run
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/case.py, line 
625 in __call__
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/suite.py, line 
125 in run
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/suite.py, line 
87 in __call__
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/suite.py, line 
125 in run
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/suite.py, line 
87 in __call__
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/suite.py, line 
125 in run
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/suite.py, line 
87 in __call__
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/unittest/runner.py, 
line 168 in run
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/support/__init__.py,
 line 1750 in _run_suite
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/support/__init__.py,
 line 1784 in run_unittest
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/regrtest.py, line 
1279 in test_runner
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/regrtest.py, line 
1280 in runtest_inner
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/regrtest.py, line 
967 in runtest
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/regrtest.py, line 
763 in main
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/regrtest.py, line 
1564 in main_in_temp_cwd
  File 
/usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/test/__main__.py, line 
3 in module
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/runpy.py, line 
85 in _run_code
  File /usr/home/db3l/buildarea/3.4.bolen-freebsd7/build/Lib/runpy.py, line 
170 in _run_module_as_main
---

See also the issue #11859 (fixed).

--
components: Tests
keywords: buildbot
messages: 226326
nosy: haypo
priority: normal
severity: normal
status: open
title: test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2
versions: Python 3.4, Python 3.5

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[issue22331] test_io.test_interrupted_write_text() hangs on the buildbot FreeBSD 7.2

[Roundup Robot]

Roundup Robot added the comment:

New changeset baa372eb731c by Victor Stinner in branch '3.4':
Issue #22331: Skip test_interrupted_write_text() on FreeBSD older than 8.0
http://hg.python.org/cpython/rev/baa372eb731c

New changeset 340d48347295 by Victor Stinner in branch 'default':
(Merge 3.4) Issue #22331: Skip test_interrupted_write_text() on FreeBSD older
http://hg.python.org/cpython/rev/340d48347295

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nosy: +python-dev

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