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From Caolan McMahon <caolan.mcma...@gmail.com>
Subject Re: CommonJS module updates
Date Tue, 22 Feb 2011 19:12:02 GMT
Thanks for the pointer ;)

https://github.com/caolan/couchdb/commit/439b6a65a4326b90307c5e0e81beacb249461420

I'm starting to think this is the safest option until we've had chance
to more widely discuss the options regarding a more persistent module
cache.



On 22 February 2011 18:14, Paul Davis <paul.joseph.davis@gmail.com> wrote:
> On Tue, Feb 22, 2011 at 1:07 PM, Caolan McMahon
> <caolan.mcmahon@gmail.com> wrote:
>> An alternative, which avoids caching modules between requests:
>> https://github.com/caolan/couchdb/commit/76c4f8ef9ab719b3d5cae22255197d06d1395756
>>
>> I'd prefer if we did cache modules between requests, but this would
>> still solve my problems ;)
>>
>>
>> On 22 February 2011 17:20, Caolan McMahon <caolan.mcmahon@gmail.com> wrote:
>>> I can see the case for not wanting to store state on modules between
>>> requests, as this could break caching rules for those resources. Even
>>> though there is a performance hit. How would you know if the results
>>> for a show or list function had changed?
>>>
>>> It also sounds like this would be unreliable anyway since there are
>>> multiple JS processes. However, I think we must have caching between
>>> require()'s within a single request, as otherwise some modules will
>>> not work and we can't handle circular dependencies.
>>>
>>> The question is, should CouchDB enforce the fact that applications
>>> should not store state between requests (except for caching) and take
>>> the performance hit, or should this be left to commonjs module
>>> developers?
>>>
>>> I assume freezing modules would cancel out the benefits of increased
>>> module compatability...
>>>
>>>
>>> On 22 February 2011 16:57, Paul Davis <paul.joseph.davis@gmail.com> wrote:
>>>> On Tue, Feb 22, 2011 at 11:47 AM, Caolan McMahon
>>>> <caolan.mcmahon@gmail.com> wrote:
>>>>> As some of you may know, I've been working on a couchapp framework
>>>>> which makes heavy use of commonjs modules (http://kansojs.org). While
>>>>> developing this I've run into a number of issues which prevent the use
>>>>> of some modules, and makes writing my own more difficult:
>>>>>
>>>>> 1. Modules are not cached - eval'ing a complex application, consisting
>>>>> of many modules on each request would have an impact on performance.
>>>>> It also means you can't use modules which use the module object to
>>>>> store state. This is commonly used by template libraries to store
>>>>> loaded templates in a cache, or 'memoize' expensive functions.
>>>>>
>>>>> 2. Circular dependencies blow the stack - Its not possible to require
>>>>> module A from module B, if module B also requires module A. This
>>>>> happens more often than you might think, and is handled by other
>>>>> require() implementations by setting the cached module to an empty
>>>>> object before eval'ing it. The fix for this requires a module cache to
>>>>> be in place.
>>>>>
>>>>>
>>>>> Since these are really hindering progress, I've forked on github and
>>>>> committed my proposed patches with associated tests:
>>>>> https://github.com/caolan/couchdb/compare/7f553e82ef...6c66675a23
>>>>>
>>>>> Please, if you have time, review the code and provide me with your feedback.
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Caolan
>>>>>
>>>>
>>>> The circular dependency section looks good.
>>>>
>>>> The bit on caching and testing that things are cached is not good on
>>>> the other hand. The way that JS processes are used you can never be
>>>> sure if it'll be the same os process handling the request. In the test
>>>> suite, its more than likely to be the same OS process because of how
>>>> the server gets restarted often and there's a single serialized
>>>> client.
>>>>
>>>> I'm a bit iffy on whether we should cache modules because that'd be a
>>>> pretty easy place to break view updates and could lead to other weird
>>>> bits in the show/list stuff. Though I also understand the concern for
>>>> avoiding all the recompilation. I wonder, is it possible to freeze the
>>>> module maybe?
>>>>
>>>
>>
>
> Looks good on first pass, though the resetModuleCache() might be
> better off being put into the handler for the reset command.
>

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