94 lines
2.2 KiB
Racket
94 lines
2.2 KiB
Racket
#lang racket/base
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;; on-disk hashtable cache.
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(require (prefix-in whalesong: "../version.rkt")
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racket/runtime-path
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racket/file
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file/md5)
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(define cache-directory-path
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(build-path (find-system-path 'pref-dir)
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"whalesong"))
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(provide cached? save-in-cache!)
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;; create-cache-directory!: -> void
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(define (create-cache-directory!)
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(unless (directory-exists? cache-directory-path)
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(make-directory* cache-directory-path)))
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;; clear-cache-files!: -> void
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;; Remove all the cache files.
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(define (clear-cache-files!)
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(for ([file (directory-list cache-directory-path)])
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(when (file-exists? (build-path cache-directory-path file))
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(with-handlers ([exn:fail? void])
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(delete-file (build-path cache-directory-path file))))))
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(define whalesong-cache.scm
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(build-path cache-directory-path
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(format "whalesong-cache-~a.scm"
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whalesong:version)))
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(define (ensure-cache-db-structure!)
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(when (not (file-exists? whalesong-cache.scm))
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;; Clear existing cache files: they're obsolete.
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(clear-cache-files!)
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(call-with-output-file whalesong-cache.scm
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(lambda (op)
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(write (make-hash) op)))))
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(define (get-db)
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(hash-copy (call-with-input-file whalesong-cache.scm read)))
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(define (write-db! hash)
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(call-with-output-file whalesong-cache.scm
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(lambda (op) (write hash op))
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#:exists 'replace))
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(create-cache-directory!)
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(ensure-cache-db-structure!)
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(define db (get-db))
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;; cached?: path -> (U false bytes)
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;; Returns a true value, (vector path md5-signature data), if we can
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;; find an appropriate entry in the cache, and false otherwise.
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(define (cached? path)
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(cond
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[(file-exists? path)
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(hash-ref db
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(list (path->string path)
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(call-with-input-file* path md5))
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#f)]
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[else
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#f]))
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;; save-in-cache!: path bytes -> void
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;; Saves a record.
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(define (save-in-cache! path data)
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(cond
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[(file-exists? path)
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(define signature (call-with-input-file* path md5))
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(hash-set! db
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(list (path->string path)
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signature)
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data)
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(write-db! db)]
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[else
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(error 'save-in-cache! "File ~e does not exist" path)])) |