1 Lisp Library Modules, Medley Release 1.0, CASH-FILE 1 Lisp Library Modules, Medley Release 1.0, CASH-FILE CASH-FILE 1 CASH-FILE 1 CASH-FILE 6 Cash-File is a front end to Hash-File which uses a hash table to cache accesses to hash files. This can provide a significant performance improvement in applications which access a small number of keys repeatedly. For example, the Where-Is library module uses this module to achieve acceptable interactive performance. Cash-File(CASH-FILE NIL Cash-File NIL NIL 15) is similar to but not compatible with the LispUsers' module, HASHBUFFER. All of the code for Cash-File is in a package called Cash-File. Througout this document Lisp symbols are printed as though in a package which uses the packages Cash-File, Hash-File, and Lisp. Installation 1 Load CASH-FILE.DFASL and HASH-FILE.DFASL from the library. Functions 1 The functional interface is designed to closely resemble that of Hash-File, which was in turn designed to resemble the Common Lisp hash table facility. (make-cash-file(MAKE-CASH-FILE (Function) make-cash-file NIL NIL 15) file-name size cache-size) [Function] Creates and returns an empty cash file in file-name. Size is passed as the size argument to make-hash-file, while cache-size is passed as the size argument to make-hash-table and determines the maximum number of entries to be cached. (get-cash-file(GET-CASH-FILE (Function) get-cash-file NIL NIL 15) key cash-file &optional default) [Function] Just like get-hash-file and gethash. Retrieves the value stored under key in cash-file or default if there is none. Also returns a second value which is true if a value was found for key. A setf method is also defined for get-cash-file . (open-cash-file file-name cache-size &key direction) [Function] Open the existing hash file in file-name in direction (:input or :io). Cache-size is passed as the size argument to make-hash-table and determines the maximum number of entries which will ever be cached. (rem-cash-file key cash-file) [Function] Like rem-hash-file and remhash. Deletes key from the hash file and the cache. Returns true if and only if there was a value stored under key. (cash-file-p object) [Function] Returns true if and only if object is a cash file. (cash-file-p object)ÿÿ ïrÿ(typep object 'cash-file) (cash-file-hash-file cash-file) [Function] Returns the hash file object to which cash-file is a front end. There are no cash file specific equivalents for close-hash-file, map-hash-file and hash-file-count. For these use the hash file functions on the cash-file-hash-file . Implementation Notes 1 A queue is maintained to enable cache deletion when the cache is full. This queue is implemented as a list. Each time a key is accessed, it is moved to the head of the queue. The last element of the queue is deleted when a new key is accessed and the queue is full. Limitations 1 The cache time is not constant but grows linearly with the size of the cache. For this reason, huge caches are not recommended. 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