bug#41242: Port feature/native-comp to Windows - Reduce the number of files probed when finding a lisp file.

[Andrea Corallo]

Nicolas Bértolo <nicolasbertolo@gmail.com> writes:

> Last night I came up with a fresh idea to properly solve the problem with slow
> loads. Considering that it happens when `load-path` contains hundreds of
> directories I thought that a caching mechanism would help.
>
> This "cache" would consist of a mapping of files that would get probed when
> (load "foo") runs. It would be implemented as a hash table. This could get
> stored in `package-user-dir` and package.el would be in charge of updating it
> when installing or removing packages, just like autoloads.
>
> The contents of this hash table could be something like this:
>
> The directory company-20200525.101 could have a file load-cache.el with:
>
> company -> ("company-20200525.101/eln-hash/company.eln"
>             "company-20200525.101/company.el"
>             "company-20200525.101/company.elc")
> [...]
>
> The directory helm-20200517.509 could have a file load-cache.el with:
>
> helm -> ("helm-20200517.509/eln-hash/helm.eln"
>          "helm-20200517.509/helm.el"
>          "helm-20200517.509/helm.elc")
> [...]
>
> When `load-path` changes we could update the in-memory hash table by loading 
> all
> the load-cache.el files.
>
> Then, when (require 'foo) runs, the loading code could look at the hash
> table and only fopen() the files associated with the feature we are loading.
> This would reduce the number of calls to fopen() from thousands to ~3 in the
> worst case.
>
> Of course, this feature would be disabled by default.
>
> What do you think?

Hi Nico,

could you recall me why this is specific to the native-comp branch?
Isn't this a problem that should affect any Emacs on Windows?

Thanks

  Andrea

-- 
akrl@sdf.org