STINNER Victor added the comment:
About the new optional balanced parameter added downstream to Fedora, the patch
is very small compared to timedlock.patch. It only changes the Python code, not
the C code:
--- /home/haypo/prog/python/2.7/Lib/threading.py 2014-11-05
15:05:11.432003853 +0100
+++ /usr/lib64/python2.7/threading.py 2015-07-05 16:16:00.000000000 +0200
@@ -306,7 +306,7 @@
else:
return True
- def wait(self, timeout=None):
+ def wait(self, timeout=None, balancing=True):
"""Wait until notified or until a timeout occurs.
If the calling thread has not acquired the lock when this method is
@@ -355,7 +355,10 @@
remaining = endtime - _time()
if remaining <= 0:
break
- delay = min(delay * 2, remaining, .05)
+ if balancing:
+ delay = min(delay * 2, remaining, 0.05)
+ else:
+ delay = remaining
_sleep(delay)
if not gotit:
if __debug__:
(with some additional changes to pass balanced parameter)
Compare:
$ diffstat balanced.patch
threading.py | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
$ diffstat timedlock.patch
Doc/library/thread.rst | 31 ++++++++++---
Doc/library/threading.rst | 32 +++++++++++++-
Include/pythread.h | 37 ++++++++++++++++
Lib/dummy_thread.py | 8 +++
Lib/multiprocessing/pool.py | 6 +-
Lib/test/lock_tests.py | 44 +++++++++++++++++--
Lib/threading.py | 25 +++--------
Modules/threadmodule.c | 53 +++++++++++++++++++----
Python/thread_nt.h | 33 +++++++++++---
Python/thread_pthread.h | 98 +++++++++++++++++++++++++++++++++++---------
10 files changed, 296 insertions(+), 71 deletions(-)
Do you know if the balanced parameter is used in the wild? Such code only works
with Python 2 on Fedora/CentOS/RHEL, right?
"For upstream, I think it would be desirable to backport the timeout argument
and simply have it throw RuntimeError if used with any of the backends other
than thread_nt and thread_pthread."
It's not how Python handles portability. There are two choices in Python:
* some functions are only available on some platforms, ex: os.fork()
* the feature is supported by all platforms and Python uses a different
implementation depending on the platform (ex: os.kill)
Raising RuntimeError depending on the platform is not a good practice.
"That way single source Python 2/3 code gains access to the timeout option,
while code relying on one of the no-longer-available-in-Python-3 threading
backends doesn't incur any stability risks."
This issue is about the performance of Condition.wait(). The timeout parameter
already exists on Python 2 in Condition.wait(). So it's already possible to
write a single code base compatible with Python 2 and Python 3.
If you are talking about adding e *new* timeout parameter to threading.Lock,
it's a new feature. Usually, we don't add new features in minor releases. It
makes maintenace more complex: you cannot guarantee anymore that an application
written for Python 2.7.x will work on Python 2.7.y. If you really want this, I
consider that a PEP is required to define exactly the scope of such change.
"However, I don't feel strongly enough about that to argue in favour of it
against opposition - I'm happy enough to confine my argument to changing the
downstream Fedora/RHEL/CentOS patch."
For this specific change (optimizing Condition.wait(timeout) using OS timeout),
it makes sense to have a downstream only patch because the change will be
specific to Linux.
Well, I'm not strongly opposed to optimize Python 2, but since the patch is not
portable, if you really want it, I consider that the topic should be discussed
on python-dev to have a wide audience.
----------
Added file: http://bugs.python.org/file40512/balanced.patch
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<http://bugs.python.org/issue25084>
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