pyflakes: undefined names, get_context() and main(), in multiprocessing

[vstinner]

BPO	20990
Nosy	@vstinner, @serhiy-storchaka

^{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 2014-03-25.21:47:19.515>
created_at = <Date 2014-03-20.08:00:03.849>
labels = ['type-bug']
title = 'pyflakes: undefined names, get_context() and main(), in multiprocessing'
updated_at = <Date 2014-03-25.21:47:19.513>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2014-03-25.21:47:19.513>
actor = 'sbt'
assignee = 'sbt'
closed = True
closed_date = <Date 2014-03-25.21:47:19.515>
closer = 'sbt'
components = []
creation = <Date 2014-03-20.08:00:03.849>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 20990
keywords = []
message_count = 8.0
messages = ['214182', '214183', '214190', '214563', '214575', '214626', '214732', '214855']
nosy_count = 5.0
nosy_names = ['vstinner', 'jnoller', 'python-dev', 'sbt', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue20990'
versions = ['Python 3.4', 'Python 3.5']

[vstinner]

Two warnings from pyflakes:

diff -r 72889bf8531d Lib/multiprocessing/spawn.py
--- a/Lib/multiprocessing/spawn.py      Tue Mar 18 13:21:29 2014 +0100
+++ b/Lib/multiprocessing/spawn.py      Wed Mar 19 11:49:24 2014 +0100
@@ -64,6 +64,7 @@ def freeze_support():
     Run code for process object if this in not the main process
     '''
     if is_forking(sys.argv):
+        # FIXME: main() is undefined
         main()
         sys.exit()
 
diff -r 72889bf8531d Lib/multiprocessing/synchronize.py
--- a/Lib/multiprocessing/synchronize.py        Tue Mar 18 13:21:29 2014 +0100
+++ b/Lib/multiprocessing/synchronize.py        Wed Mar 19 11:50:50 2014 +0100
@@ -51,7 +51,6 @@ class SemLock(object):
     _rand = tempfile._RandomNameSequence()
 
     def __init__(self, kind, value, maxvalue, *, ctx):
-        ctx = ctx or get_context()
         ctx = ctx.get_context()
         unlink_now = sys.platform == 'win32' or ctx._name == 'fork'
         for i in range(100):

[vstinner]

Serhiy suggested (msg214136):

"Lib/multiprocessing/synchronize.py:
Add at the start of the file:
from . import get_context"

It looks like multiprocessing.get_context() exists, but I don't see how it is defined.

For main(), it should maybe be replaced with _main()?

[serhiy-storchaka]

It looks like multiprocessing.get_context() exists, but I don't see how it
is defined.

It is defined by:

globals().update((name, getattr(context._default_context, name))
for name in context._default_context.__all__)

For main(), it should maybe be replaced with _main()?

_main() has different signature.

[python-dev]

New changeset 619331c67638 by Richard Oudkerk in branch '3.4':
Issue bpo-20990: Fix issues found by pyflakes for multiprocessing.
http://hg.python.org/cpython/rev/619331c67638

[vstinner]

Would it be possible to write a test?

Le dimanche 23 mars 2014, Roundup Robot <report@bugs.python.org> a écrit :

Roundup Robot added the comment:

New changeset 619331c67638 by Richard Oudkerk in branch '3.4':
Issue bpo-20990: Fix issues found by pyflakes for multiprocessing.
http://hg.python.org/cpython/rev/619331c67638

----------
nosy: +python-dev

---

Python tracker <report@bugs.python.org <javascript:;>>
<http://bugs.python.org/issue20990\>

---

[python-dev]

New changeset bb6377db0a9e by Richard Oudkerk in branch '3.4':
Issue bpo-20990: Correction for 619331c67638.
http://hg.python.org/cpython/rev/bb6377db0a9e

[vstinner]

Can we close this issue? Or Richard wants to write a test?

[sbt]

Testing the is_forking() requires cx_freeze or something similar, so it really cannot go in the test suite.

I have tested it manually (after spending too long trying to get cx_freeze to work with a source build).

It should be noted that on Unix freezing is currently only compatible with the default 'fork' start method.