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From Caolan McMahon <>
Subject Re: CommonJS module updates
Date Tue, 22 Feb 2011 18:07:25 GMT
An alternative, which avoids caching modules between requests:

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 <> 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 <> wrote:
>> On Tue, Feb 22, 2011 at 11:47 AM, Caolan McMahon
>> <> wrote:
>>> As some of you may know, I've been working on a couchapp framework
>>> which makes heavy use of commonjs modules ( 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:
>>> 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?

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