[Twisted-Python] In memory cache in twisted

[Ilya Skriblovsky]

Hi all,

Here is async in-memory cache that I've implemented for one of my projects:
https://gist.github.com/IlyaSkriblovsky/5aba53b661acd49b65efeb4ce41a8b52

It properly handles problem #2 described by Maarten. But it doesn't
bother with eviction because it wasn't needed at the time of writing
(because key space was limited).

Usage example:

    @defer.inlineCallbacks
    def load_content(url: str):
        # does some long-running async task such as loading url content

    @defer.inlineCallbacks
    def main():
        # DeferredCache receives loader function as an argument
        # Loader function must return Deferred
        cache = DeferredCache(load_content)

        # this will actually download content
        page1 = yield cache.get('http://example.com')
        # this will use cached one (note that this get() also returns
Deferred, but that
        # Deferred will be already-succeeded, so `yield` will return
the content immediately)
        page2 = yield cache.get('http://example.com')

        # illustration of problem #2 described by Maarten
        # note there is no yield here, we are running these to get()s
simultaneously
        deferred_page1 = cache.get('https://www.nasa.gov/')
        deferred_page2 = cache.get('https://www.nasa.gov/')
        # actually waiting for results
        page1, page2 = yield deferred.gatherResults([deferred_page1,
deferred_page2])
        # load_content() will be called only once with
'https://www.nasa.gov/' by this point

-- Ilya

пт, 27 сент. 2019 г. в 06:59, Maarten ter Huurne <maarten at treewalker.org>:
>
> On Friday, 27 September 2019 05:48:35 CEST Waqar Khan wrote:
> > Hi Maarten,
> >    I think you have hit the problem in the head. I do think this is
> > feasible as I have observed that as size of cache increases, things do
> > get better which might support your theory.
> >
> > Is there a simple example you can add on "put a Deferred for the fetch
> > operation ". I am really just getting started with twisted.
> > Thanks for all the help.
>
> Unfortunately I don't think I have any code lying around that implements
> this kind of cache.
>
> Bye,
>                 Maarten
>
>
>
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