On Apr 28, 2020, at 16:25, Steven D'Aprano <[email protected]> wrote:
>
> On Tue, Apr 28, 2020 at 11:45:49AM -0700, Raymond Hettinger wrote:
>
>> It seems like you would get just about everything you want with one line:
>>
>> once = lru_cache(maxsize=None)
>
> But is it thread-safe?
You can add thread safety the same way as any other function:
@synchronized
@once
def spam():
return 42 in a slow and non-thread-safe and non-idempotent way and also
launch the missiles the second time we’re called
Or wrap a with lock: around the code that calls it, or whatever.
Not all uses of once require thread safety. For the really obvious example,
imagine you’re sharing a singleton between coroutines instead of threads. And
if people are really concerned with the overhead of lru_cache(maxsize=None),
the overhead of locking every time you access the value is probably even less
acceptable when unnecessary.
So, I think it makes sense to leave it up to the user (but to explain the issue
in the docs). Or maybe we could add a threading.once (and asyncio.once?) as
well as functools.once?
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