[Python-3000] Useless methods in Queue module
mike.klaas at gmail.com
Tue Jan 15 03:31:08 CET 2008
On 14-Jan-08, at 5:49 PM, Jeffrey Yasskin wrote:
> On Jan 14, 2008 2:55 PM, Mike Klaas <mike.klaas at gmail.com> wrote:
>> This is a misleading name. The number returned from qsize() [not
>> ()] is perfectly reliable, in the sense that it is the exact size of
>> the queue at some instant in time.
> No, you're wrong. In CPython's implementation, it's likely that qsize
> is implemented by locking the structure and reading a size field,
It isn't likely, it is. It is also implemented as such in all
mainstream python interpreters (ironpython, jython), since they use
CPython's pure-python implementation.
I grant that it is theoretically possible to implement Queue.Queue's
full interface with a data structure in which qsize() is never a
consistent length of the index at a given time, even if such a
structure may not yet exist.
> Furthermore, it's misleading to think of even a locked
> implementation's result as reliable. Ignoring problems with
> simultaneity in the presence of threads, the "true" value could easily
> have changed by the time qsize returns. And if it returns a value
> that's not accurate, that can hardly be described as reliable. It
> really is returning an estimate of the size, suitable only for use in
> performance optimizations where you're prepared to handle it sometimes
> being wildly wrong.
In some usage patterns it is thread-unsafe. Whether this means that
the method itself is "unreliable" is a battle likely not worth
getting in to.
Thanks for the interesting reference,
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