From: "Ludovic Courtès" <ludo@gnu.org>
To: Maxime Devos <maximedevos@telenet.be>
Cc: 50384@debbugs.gnu.org
Subject: [bug#50384] [PATCH] Optimise search-patch (reducing I/O)
Date: Sun, 05 Sep 2021 00:04:25 +0200 [thread overview]
Message-ID: <87tuj0xaja.fsf@gnu.org> (raw)
In-Reply-To: <8900fa8c8eef7f72fc97adc2408be26c88de7803.camel@telenet.be> (Maxime Devos's message of "Sat, 04 Sep 2021 23:17:10 +0200")
Maxime Devos <maximedevos@telenet.be> skribis:
> +(define-syntax search-patch
> + (lambda (s)
> + "Search the patch FILE-NAME and compute its hash at expansion time
> +if possible. Return #f if not found."
> + (syntax-case s ()
> + ((_ file-name)
> + (string? (syntax->datum #'file-name))
> + ;; FILE-NAME is a constant string, so the hash can be computed
> + ;; in advance.
> + (let ((patch (try-search-patch (syntax->datum #'file-name))))
> + (if patch
> + #`(%local-patch-file file-name #,(file-hash* patch #:select? true))
> + (begin
> + (warning (source-properties->location
> + (syntax-source #'file-name))
> + (G_ "~a: patch not found at expansion time")
> + (syntax->datum #'ile-name))
> + #'(%search-patch file-name)))))
> + ;; FILE-NAME is variable, so the hash cannot be pre-computed.
> + ((_ file-name) #'(%search-patch file-name))
> + ;; search-patch is being used used in a construct like
> + ;; (map search-patch ...).
> + (id (identifier? #'id) #'%search-patch))))
It’s clever… but also a bit evil, in that it changes the semantics of
package files in a surprising way. Modifying foo.patch without
recompiling foo.scm would lead you to still use the old foo.patch, which
can be rather off-putting and error-prone IMO.
To address this, ‘local-file’ could store the inode/mtime + computed
store file name (rather than the SHA256). ‘local-file-compiler’ would
check whether the actual file has matching inode/mtime before returning
the computed store file name. Problem is that inode/mtime are
guaranteed to differ once you’ve run “make install”. :-/
Intuitively, I’d have imagined a cache populated at run time; it would
map, say, file name/inode/mtime to a store file name. ‘add-to-store’
(or some wrapper above it) would check the cache and return the store
file name directly, unless ‘valid-path?’ says it no longer exists.
Downside is that this would be a per-user cache and you’d still pay the
cost until it’s warm. Advantage is that you could easily tell whether
it’s stale.
Thoughts?
Ludo’.
next prev parent reply other threads:[~2021-09-04 22:05 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-04 21:17 [bug#50384] [PATCH] Optimise search-patch (reducing I/O) Maxime Devos
2021-09-04 21:47 ` Ludovic Courtès
2021-09-04 22:04 ` Ludovic Courtès [this message]
2021-09-05 19:48 ` [bug#50384] [PATCH v2] " Maxime Devos
2021-09-05 22:40 ` Maxime Devos
2021-09-06 8:39 ` zimoun
2021-09-06 10:06 ` Maxime Devos
2021-09-09 14:51 ` [bug#50384] [PATCH] " Ludovic Courtès
2021-09-21 16:55 ` [bug#50384] [PATCH v4] " Ludovic Courtès
2021-09-23 17:26 ` Maxime Devos
2021-09-27 16:17 ` Ludovic Courtès
2021-10-04 16:46 ` [bug#50384] [PATCH] " zimoun
2021-10-08 7:41 ` Ludovic Courtès
2021-10-11 8:09 ` [bug#39258] bug#50384: " zimoun
2021-09-09 20:25 ` [bug#50384] [PATCH v3] " Maxime Devos
2021-09-10 9:54 ` bug#50384: " Maxime Devos
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