My contributions to CPython during 2017 Q3: Part 1

My contributions to CPython during 2017 Q3 (july, august, september), Part 1.

Previous report: My contributions to CPython during 2017 Q2 (part1).

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Summary:

  • Statistics
  • Security fixes
  • Enhancement: socket.close() now ignores ECONNRESET
  • Removal of the macOS job of Travis CI
  • New test.pythoninfo utility
  • Revert commits if buildbots are broken
  • Fix the Python test suite

Statistics

# All branches
$ git log --after=2017-06-30 --before=2017-10-01 --reverse --branches='*' --author=Stinner|grep '^commit ' -c
209

# Master branch only
$ git log --after=2017-06-30 --before=2017-10-01 --reverse --author=Stinner origin/master|grep '^commit ' -c
97

Statistics: I pushed 97 commits in the master branch on a total of 209 commits, remaining: 112 commits in the other branches (backports, fixes specific to Python 2.7, security fixes in Python 3.3 and 3.4, etc.)

Security fixes

  • bpo-30947: Update libexpat from 2.2.1 to 2.2.3. Fix applied to master, 3.6, 3.5, 3.4, 3.3 and 2.7 branches! Expat 2.2.2 and 2.2.3 fixed multiple security vulnerabilities. http://python-security.readthedocs.io/vuln/expat_2.2.3.html
  • Fix whichmodule() of _pickle: : _PyUnicode_FromId() can return NULL, replace Py_INCREF() with Py_XINCREF(). Fix coverity report: CID 1417269.
  • bpo-30860: _PyMem_Initialize() contains code which is never executed. Replace the runtime check with a build assertion. Fix Coverity CID 1417587.

See also my python-security website.

Enhancement: socket.close() now ignores ECONNRESET

bpo-30319: socket.close() now ignores ECONNRESET. Previously, many network tests failed randomly with ConnectionResetError on socket.close().

Patching all functions calling socket.close() would require a lot of work, and it was surprising to get a "connection reset" when closing a socket.

Who cares that the peer closed the connection, since we are already closing it!?

Note: socket.close() was modified in Python 3.6 to raise OSError on failure (bpo-26685).

Removal of the macOS job of Travis CI

call_method microbenchmark

While the Linux jobs of Travis CI usually takes 15 minutes, up to 30 minutes in the worst case, the macOS job of Travis CI regulary took longer than 30 minutes, sometimes longer than 1 hour.

While the macOS job was optional, sometimes it gone mad and prevented a PR to be merged. Cancelling the job marked Travis CI as failed on a PR, so it was still not possible to merge the PR, whereas, again, the job is marked as optional ("Allowed Failure").

Moreover, when the macOS job failed, the failure was not reported on the PR, since the job was marked as optional. The only way to notify a failure was to go to Travis CI and wait at least 30 minutes (whereas the Linux jobs already completed and it was already possible merge a PR...).

I sent a first mail in June: [python-committers] macOS Travis CI job became mandatory?

In september, we decided to remove the macOS job during the CPython sprint at Instagram (see my previous New C API article), to not slowdown our development speed (bpo-31355). I sent another email to announce the change: [python-committers] Travis CI: macOS is now blocking -- remove macOS from Travis CI?.

After the sprint, it was decided to not add again the macOS job, since we have 3 macOS buildbots. It's enough to detect regressions specific to macOS.

After the removal of the macOS end, at the end of september, Travis CI published an article about the bad performances of their macOS fleet: Updating Our macOS Open Source Offering. Sadly, the article confirms that the situation is not going to evolve quickly.

New test.pythoninfo utility

To understand the "Segfault when readline history is more then 2 * history size" crash of bpo-29854, I modified test_readline to log libreadline versions. I also added readline._READLINE_LIBRARY_VERSION. My colleague Nir Soffer wrote the final readline fix: skip the test on old readline versions.

As a follow-up of this issue, I added a new test.pythoninfo program to log many information to debug Python tests (bpo-30871). pythoninfo is now run on Travis CI, AppVeyor and buildbots.

Example of output:

$ ./python -m test.pythoninfo
(...)
_decimal.__libmpdec_version__: 2.4.2
expat.EXPAT_VERSION: expat_2.2.4
gdb_version: GNU gdb (GDB) Fedora 8.0.1-26.fc26
locale.encoding: UTF-8
os.cpu_count: 4
(...)
time.timezone: -3600
time.tzname: ('CET', 'CEST')
tkinter.TCL_VERSION: 8.6
tkinter.TK_VERSION: 8.6
tkinter.info_patchlevel: 8.6.6
zlib.ZLIB_RUNTIME_VERSION: 1.2.11
zlib.ZLIB_VERSION: 1.2.11

test.pythoninfo can be easily extended to log more information, without polluting the output of the Python test suite which is already too verbose and very long.

Revert commits if buildbots are broken

Thanks to my work done last months on the Python test suite, the buildbots are now very reliable. When a buildbot fails, it becomes very likely that it's a real regression, and not a random failure caused by a bug in the Python test suite.

I proposed a new rule: revert a change if it breaks builbots and the but cannot be fixed easily:

So I would like to set a new rule: if I'm unable to fix buildbots failures caused by a recent change quickly (say, in less than 2 hours), I propose to revert the change.

It doesn't mean that the commit is bad and must not be merged ever. No. It would just mean that we need time to work on fixing the issue, and it shouldn't impact other pending changes, to keep a sane master branch.

[python-committers] Revert changes which break too many buildbots.

test_datetime

The first revert was an enhancement of test_datetime, bpo-30822:

commit 98b6bc3bf72532b784a1c1fa76eaa6026a663e44
Author: Utkarsh Upadhyay <mail@musicallyut.in>
Date:   Sun Jul 2 14:46:04 2017 +0200

    bpo-30822: Fix testing of datetime module. (#2530)

    Only C implementation was tested.

I wrote an email to announce the revert: [python-committers] Revert changes which break too many buildbots.

It took 15 days to decide how to fix properly the issue (exclude tzdata from test resources). I don't regret my revert, since having broken buildbots for 15 days would be very annoying.

python-gdb.py fix

I also reverted this commit of bpo-30983:

commit 2e0f4db114424a00354eab889ba8f7334a2ab8f0
Author: Bruno "Polaco" Penteado <polaco@gmail.com>
Date:   Mon Aug 14 23:14:17 2017 +0100

    bpo-30983: eval frame rename in pep 0523 broke gdb's python extension (#2803)

    pep 0523 renames PyEval_EvalFrameEx to _PyEval_EvalFrameDefault while the gdb python extension only looks for PyEval_EvalFrameEx to understand if it is dealing with a frame.

    Final effect is that attaching gdb to a python3.6 process doesnt resolve python objects. Eg. py-list and py-bt dont work properly.

    This patch fixes that. Tested locally on python3.6

My comment on the issue:

I chose to revert the change because I don't have the bandwidth right now to investigate why the change broke test_gdb.

I'm surprised that a change affecting python-gdb.py wasn't properly tested manually using test_gdb.py :-( I understand that Travis CI doesn't have gdb and/or that the test pass in some cases?

The revert only gives us more time to design the proper solution.

Hopefully, a new fixed commit was pushed 4 days later and this one didn't break buildbots!

Fix the Python test suite

As usual, I spent a significant part of my time to fix bugs in the Python test suite to make it more reliable and more "usable".

  • bpo-30822: Exclude tzdata from regrtest --all. When running the test suite using --use=all / -u all, exclude tzdata since it makes test_datetime too slow (15-20 min on some buildbots, just this single test file) which then times out on some buildbots. -u tzdata must now be enabled explicitly.

  • bpo-30188, test_nntplib: Catch also ssl.SSLEOFError in NetworkedNNTPTests.setUpClass(), not only EOFError. (Sadly, test_nntplib still fails randomly with EOFError or SSLEOFError...)

  • bpo-31009: Fix support.fd_count() on Windows. Call msvcrt.CrtSetReportMode() to not kill the process nor log any error on stderr on os.dup(fd) if the file descriptor is invalid.

  • bpo-31034: Reliable signal handler for test_asyncio. Don't rely on the current SIGHUP signal handler, make sure that it's set to the "default" signal handler: SIG_DFL. A colleague reported me that the Python test suite hangs on running test_subprocess_send_signal() of test_asyncio. After analysing the issue, it seems like the test hangs because the RPM package builder ignores SIGHUP.

  • bpo-31028: Fix test_pydoc when run directly. Fix get_pydoc_link(): get the absolute path to __file__ to prevent relative directories.

  • bpo-31066: Fix test_httpservers.test_last_modified(). Write the temporary file on disk and then get its modification time.

  • bpo-31173: Rewrite WSTOPSIG test of test_subprocess.

    The current test_child_terminated_in_stopped_state() function test creates a child process which calls ptrace(PTRACE_TRACEME, 0, 0) and then crash (SIGSEGV). The problem is that calling os.waitpid() in the parent process is not enough to close the process: the child process remains alive and so the unit test leaks a child process in a strange state. Closing the child process requires non-trivial code, maybe platform specific.

    Remove the functional test and replaces it with an unit test which mocks os.waitpid() using a new _testcapi.W_STOPCODE() function to test the WIFSTOPPED() path.

  • bpo-31008: Fix asyncio test_wait_for_handle on Windows, tolerate a difference of 50 ms.

  • bpo-31235: Fix ResourceWarning in test_logging: always close all asyncore dispatchers (ignoring errors if any).

  • bpo-30121: Add test_subprocess.test_nonexisting_with_pipes(). Test the Popen failure when Popen was created with pipes. Create also NONEXISTING_CMD variable in test_subprocess.py.

  • bpo-31250, test_asyncio: fix EventLoopTestsMixin.tearDown(). Call doCleanups() to close the loop after calling executor.shutdown(wait=True).

  • test_ssl: Implement timeout in ssl_io_loop(). The timeout parameter was not used.

  • bpo-31448, test_poplib: Call POP3.close(), don't close close directly the sock attribute to fix a ResourceWarning.

  • os.test_utime_current(): tolerate 50 ms delta.

  • bpo-31135: ttk: fix LabeledScale and OptionMenu destroy() method. Call the parent destroy() method even if the used attribute doesn't exist. The LabeledScale.destroy() method now also explicitly clears label and scale attributes to help the garbage collector to destroy all widgets.

  • bpo-31479: Always reset the signal alarm in tests. Use the try: ... finally: signal.signal(0) pattern to make sure that tests don't "leak" a pending fatal signal alarm. Move some signal.alarm() calls into the try block.

Next report: My contributions to CPython during 2017 Q3: Part 2 (dangling threads).

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