./python Doc/includes/mp_benchmarks.py

       ######## testing Array("i", ..., lock=False)

Traceback (most recent call last):
  File "Doc/includes/mp_benchmarks.py", line 235, in <module>
    test()
  File "Doc/includes/mp_benchmarks.py", line 203, in test
    test_seqspeed(multiprocessing.Array('i', range(10), lock=False))
  File
"/home/heimes/dev/python/release26-maint/Lib/multiprocessing/__init__.py",
line 254, in Array
    return Array(typecode_or_type, size_or_initializer, **kwds)
  File
"/home/heimes/dev/python/release26-maint/Lib/multiprocessing/sharedctypes.py",
line 87, in Array
    assert hasattr(lock, 'acquire')
AssertionError

The assertion error occurs when using Python 2.6 and our backports to
2.4 and 2.5.

The examples in 3.0 didn't work at at all because nobody did a 2to3 run
on them. See r67417: mp_benchmarks, mp_newtypes and mp_distribution are
still broken but the others are working properly. We should include the
examples in our unit test suite ...

The 3.0 doc/example issue is in issue 3256

I plan on fixing all the doc/example issue this/next week.

Are you able to fix the examples before 3.0.0 and 2.6.1 are released?
They are scheduled for Wednesday 3rd of December.

Yes, I have a pending patch. I'll see if I can steal some time today
to check it in.

On Fri, Nov 28, 2008 at 9:36 AM, Christian Heimes
<report@bugs.python.org> wrote:
>
> Christian Heimes <lists@cheimes.de> added the comment:
>
> Are you able to fix the examples before 3.0.0 and 2.6.1 are released?
> They are scheduled for Wednesday 3rd of December.
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue4449>
> _______________________________________
>

I guess you just 2to3'ed the examples

Jesse, please apply so we can close this issue.

This is a documentation bug, not a library bug, right? (unless someone
claims that the documentation is right and the library is wrong)

So: a) this seems to be a duplicate of issue 3256, and b) it's "just" a
documention bug. Not sure why this is marked as release blocker.

This is not a doc bug - in actuality, the mp_benchmarks.py example is 
exposing an assertion error in sharedctypes.py.

The doc-related bugs Christian and I spoke about have been fixed, however 
the main issue for this (the assertion error) is still in the code, and I 
haven't had a chance to trace it down and fix it.

Jesse, does this affect Python 3.0?  If not, then I will lower the
priority and release 2.6.1 without it (there's always 2.6.2 :).

If so, then we need to know if 1) it's really a release blocker; 2) what
the ETA on a fix is.  I would like to tag the 3.0 branch today.

2.6.0 shipped with the assertion error. Unfortunately, I'm tapped out at 
the day job right now, so I won't have a fix prepped and tested in time.

Here is a patch nonetheless. It makes the code match the the documentation:

http://docs.python.org/library/multiprocessing.html#multiprocessing.sharedctypes.Arra
y
"""
- If lock is True (the default) then a new lock object is created to synchronize 
access to the value.
- If lock is a Lock or RLock object then that will be used to synchronize access to 
the value.
- If lock is False then access to the returned object will not be automatically 
protected by a lock, so it will not necessarily be process-safe.
"""

I changed multiprocessing.sharedctypes.Array and multiprocessing. sharedctypes.Array
I had to change some tests: now "lock=None" is an error.
+ some markup fixes in the documentation.

The patch looks fine. However I propose to replace the assert statement
with a proper check that raises a meaningful exception.

if not hasattr(lock, 'acquire'):
    raise AttributeError("'%r' has no method 'acquire'" % lock)

+1 on Amaury's patch, however I wouldn't change the assert right now - Christian's suggestion does make sense to change globally post 3.0

Amaury, do you want to submit it?

I don't much like the

lock is True
lock is False

idioms much, but I don' thave a better suggestion, and it would be nice
to fix this for the releases.

Indeed, it seems that multiprocessing uses assertions in many places to 
handle errors in user code. This could be changed, but it is another 
task.

I can apply the patch, but what about 2.6? it's an incompatible API 
change, unless we choose to process "lock=None" the same way as 
"lock=False".

Does the language guarantee that True and False are singletons (to
support the is-test for identity)?  Does this API port to Jython and
IronPython?  Is it a problem that 1 cannot be substituted for True?

The one I know is pypy: bool(x) always return one of the two prebuilt singletons 
(doubletons?).

The docs explicitly mention "If lock is True...", "If lock is False...":
http://docs.python.org/library/multiprocessing.html#multiprocessing.sharedctypes.Value

I fear that testing the boolean value of the lock variable may have undesired effect; if 
even the main multiprocessing.RLock object has a _is_zero() method (that seems to return 
whether the lock is held or not), it is very possible that other implementations choose 
__nonzero__ for this.

I've changed my mind based on the API change.  This should be discussed
on the mailing list and deferred until 2.6.2 at least.

What about this other patch:
- lock=None has the same semantics as before
- lock=True is the same as lock=None (it failed before)
- lock=False return the object without the "synchronized" wrap (it 
failed before)
- no need to change previous tests

I think Amaury's patch (mp_array_2.patch) is correct. If there is no
objection to its acceptance within the next two days, I think it should
be applied.

I agree with Martin - if no one else gets to this before me, I should be 
able to submit it within the next day.

FYI, there was a small issue in the patch - namely the only way to get 
the 
AttributeError to raise in the Value/Array creation is to not pass in a 
lock, True/None - the latter two get to a lock/RLock while the 
former will have the acquire method. If you pass in False, you 
immediately get the RawValue() object back.

I changed the test to reflect this:

    self.assertRaises(AttributeError, self.Value, 'i', 5, 
lock='navalue')
    self.assertRaises(AttributeError,
                      self.Array, 'i', range(10), lock='notalock')

Checked into trunk in r68708 - I pinged benjamin to see how we're handling 
merges right now as this needs to go into py3k