67 lines
2.5 KiB
EmacsLisp
67 lines
2.5 KiB
EmacsLisp
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;;; cache-table.el --- a hash table with expiring entries -*- lexical-binding: t; -*-
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;; This is free and unencumbered software released into the public domain.
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;; Author: Christopher Wellons <mosquitopsu@gmail.com>
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;; Version: 1.0
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;;; Commentary:
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;; See the docstring of `cache-table-create'. There is no
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;; `cache-table-put': use `setf' on `cache-table-get' instead.
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;;; Code:
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(require 'cl-lib)
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(cl-defstruct (cache-table (:constructor cache-table--create))
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"A cache table with expiring entries."
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expire-time table)
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(defun cache-table-create (expire-time &rest keyword-args)
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"Create a new cache-table with entries automatically removed
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from the table after EXPIRE-TIME seconds. This function accepts
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the same keyword arguments as `make-hash-table'. Entries are not
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actually removed from the cache-table until an access is made to
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the cache-table.
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Use `cache-table-get' to get and put (via setf) entries."
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(cache-table--create :expire-time expire-time
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:table (apply #'make-hash-table keyword-args)))
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(defun cache-table-clear-expired (cache-table)
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"Remove all expired entries from CACHE-TABLE."
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(cl-loop with expire-time = (cache-table-expire-time cache-table)
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with table = (cache-table-table cache-table)
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with dead-time = (- (float-time) expire-time)
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for key being the hash-keys of table using (hash-value entry)
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for (time . value) = entry
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when (< time dead-time) do (remhash key table)))
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(defun cache-table-get (key cache-table &optional default)
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"Access the value for KEY in CACHE-TABLE if it has not yet
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expired. Behaves just like `gethash'."
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(cache-table-clear-expired cache-table)
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(cdr (gethash key (cache-table-table cache-table) (cons 0 default))))
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(gv-define-setter cache-table-get (value key cache-table)
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"Put an entry in the hash table, like (setf (gethash key table) value)."
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`(progn
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(cache-table-clear-expired ,cache-table)
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(puthash ,key (cons (float-time) ,value)
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(cache-table-table ,cache-table))))
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(defun cache-table-map (f cache-table)
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"Like `maphash', call F for all non-expired entries in CACHE-TABLE."
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(cache-table-clear-expired cache-table)
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(maphash (lambda (k v) (funcall f k (cdr v)))
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(cache-table-table cache-table)))
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(defun cache-table-count (cache-table)
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"Like `hash-table-count', count the number of non-expired entries."
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(hash-table-count (cache-table-table cache-table)))
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(provide 'cache-table)
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;;; cache-table.el ends here
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