Common-Lisp-Persistency-Manager

A File-Based Fully Automatic Lisp Datastructure Serializer / Persistency Manager, Similar to "Pickle" for Python

About

Another piece of Common Lisp legacy software from my quarter century-old Lisp archive :-) It still works flawlessly in 2021 (tested with LispWorks 6.1 on Ubuntu).

This software package allows you to serialize / "persist" arbitary Common Lisp datastructures to disc, and read them back, without having to write a single line of code. It supports CLOS classes and structures, hash tables, arrays, vectors, symbols, numbers, lists, conses, etc.

For example, simple Common Lisp datatypes can be serialized as follows:

(defun test ()

  (make-object-persistent 
     (list 'symbol 123 'test "abcdef" 123.3 4/3 
	   (list 'a 1 2 'b "xyz"))
     "pertest")

  (load-persistent-object "pertest"))

Cyclic data structures are no problem either!

It also serializes vectors, hashtables, and CLOS classes that have been defined with the macros defpersistentclass and defpersistentstruct. For CLOS classes:

(defpersistentclass test ()
  ((a :accessor a :initarg :a)
   (b :accessor b :initarg :b)))

(defpersistentclass test2 (test)
  ((c :accessor c :initarg :c)))

(defun run-test ()

  (setf table 
	(let ((table
	       (make-hash-table :test #'equal
				:size 100
				:rehash-size 100)))
	  (loop as i from 1 to 100 do
	       (setf (gethash (list i i i) table)
		     (loop as j from 1 to (+ i 10) collect 
			  (list (* j j )
				(- (* j j ))))))
	  table))

  (setf x (make-instance 'test
			 :a table))

  (setf y (make-instance 'test
			 :a x 
			 :b (make-array '(10))))

  (setf z (make-instance 'test2
			 :c (list x y
				  (make-array '(3)
					      :initial-contents (list x y x)))))

  (setf orig 
	(vector x y z 
		(list x table (vector x z y) x z)))

  (make-object-persistent orig "test")

  (setf copy (load-persistent-object "test")))

For structures:

(defpersistentstruct stest 
                     (a)
                     (b))

(defpersistentstruct (stest2 (:include stest))
                     (c))


(defun run-stest ()
  (setf table
	(let ((table 
	       (make-hash-table :test #'equal
				:size 100
				:rehash-size 100)))
	  (loop as i from 1 to 100 do
	       (setf (gethash (list i i i) table)
		     (loop as j from 1 to (+ i 10) collect (* j j ))))
	  table))

  (setf x (make-stest
           :a table))

  (setf y (make-stest :a x
                      :b
                      (make-array '(10))))

  (setf z (make-stest2 :c (list x y
                                (make-array '(3)
                                            :initial-contents (list x y x)))))

  (setf orig (vector x y z (list x table (vector x z y) x z)))

  (make-object-persistent orig "test")

  (setf copy (load-persistent-object "test")))

Loading / Usage

Adjust the logical pathname translations in persistence-sysdcl.lisp to match your environment. Then, simply do a (load "persistence:persistence-sysdcl.lisp"). This also runs a few tests. You will need a larger stack size (i.e., in the 500 KB range).

History

There was a time in software development when you had to write your own libraries, even for something as fundamental like a Python pickle that many programmers take for granted nowadays. Well, in 1995, I had to write my own Common Lisp pickle, simply because such a functionality didn't exist!

I started writing complex Common Lisp applications in 1994. For my first complex Common Lisp CLIM application (the graphical editor "GenEd") I still had to write a large number of serializers / deserializers by hand. Given the large number of CLOS classes for its graphical objects, this was a tedious endeavor and not enjoyable. I already knew about the MOP (Metaobject Protocol) and an approach developed by a university colleague, Heiko Kirschke, called "PLOB" (Persistent Lisp Objects), but figured that his solution to the problem was a little bit too sophisticated for my use cases (PLOB required a full-fledged relational database and used the not-so-well supported and not standardized Metaobject Protocol, which made the approach not very portable).

I hence decided to create my own little persistency manager, just good enough for my own purposes, to save me time. I knew enough about macros and garbage collection (and the object graph), so I was able to write defpersistentclass. I figured out how to deal with cyclic references, and to my surprise, it worked out surprisingly well. I could even store whole city maps of a few hundred KBs with my persistency manager! So, for the accompanying program of my dipoma thesis (the Visual Spatial Query Lanaguage "VISCO") I was already using this software.

Later on, my colleague (and later boss) Ralf Möller extended the persistency manager support for more data structures, e.g., packages. This extended persistency manager was then used in the Racer description logic reasoner for its "persistency layer". Racer later became RacerPro, which is available on GitHub as OpenSource as well. RacerPro's racer-persistence.lisp persistency package is this extended version.

Since 1998, I have used this small software package for every Common Lisp / CLIM application that I wrote. You can also find it in my Tangram Solver where it provides the save & load functionality.

The persistency maanger has successfully been used with LispWorks, SBCL, Allegro, MCL, and Common Lisp.

Later, companies such as Franz Inc. (makers of Allegro Common Lisp) were beginning to offer industrial-grade persistency packages, i.e., "AllegroCache". However, none of this was available to me in 1996, and AllegroCache appeared much later. And honestly, I don't need it for what I am developing. Something simpler is doing equally well (if not better).

Also, I remember that Arthur Lemmens gave a presentation about a very similar software package at the European Common Lisp Meeting in my home town, Hamburg, in April 2006. My software package preceeded his presentation by almost 10 years, and I never gave a presentation about it.

For RacerPro, starting in 2005, we have used this sofware for our license checker. Before becoming OpenSource, RacerPro was commercial, until 2013, and required a software license for proper operation that needed to be purchased from Racer Systems. The .lic license file format was actually a serialized license class CLOS object, produced by this persistency manager. The defpersistentclass racer-license object detailed the properties and permissions granted by the license (e.g., unlocked features, expiriation date, type of product, license owner, etc.) We obscured the serialization by using a higher-base number format (I believe it was a base-26 encoding). No customer ever managed to crack or temper with the licenses :-)

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