jim at digicool
Jul 22, 1999, 7:47 AM
Post #1 of 1
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Re: I'd like list.pop to accept an optional second argument giving a defaultvalue
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Skip Montanaro wrote:
>
> Jim> I like the list pop method because it provides a way to use lists
> Jim> as thread safe queues and stacks (since append and pop are
> Jim> protected by the global interpreter lock).
>
> The global interpreter lock is a property of the current implementation of
> Python, not of the language itself. At one point in the past Greg Stein
> created a set of patches that eliminated the lock. While it's perhaps
> convenient to use now, it may not always exist. I'm not so sure that it
> should be used as a motivator for changes to libraries in the standard
> distribution.
If the global interpreter lock goes away, then some other locking mechanism
will be used to make built-in object operations atomic. For example, in
Greg's changes, each list was protected by a list lock. The key is that
pop combines checking for an empty list and removing an element
into a single operation. As long as the operations append and pop are atomic,
then lists can be used as thread-safe stacks and queues.
The benefit of the proposal does not really depend on the global interpreter
lock. It only depends on list operations being atomic.
Jim
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