Christian Thaeter's persistence library
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LGPL/persistence.yap
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309
LGPL/persistence.yap
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/*
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persistence.yap - make assertions and retracts persistent
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Copyright (C) 2006, Christian Thaeter <chth@gmx.net>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License version 2 as
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published by the Free Software Foundation.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, contact me.
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*/
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:- module(persistence,
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[
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persistent_open/3,
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persistent_close/1,
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persistent_assert/1,
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persistent_retract/1
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]).
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:- use_module(library(system),[]).
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:- dynamic(persistent_desc/2).
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/*
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persistent_open(PredDesc, File, Opts).
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declare Module:Functor/Arity (Functor/Arity) to be persistent
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stored in File's (*.db *.log *log.$PID *.lock *.bak)
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Opts are:
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db - use dbfile (flat file containing all persistent predicates)
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log - use logfile (logfile with either +(Term) for asserts and -(Term) for retracts)
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bak - make backupfiles when regenerating the dbfile
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sync - flush data always
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ro - readonly, can load locked files, never changes data on disk
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wo - (planned) writeonly, implies [log], data is only written to the log and not
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asserted into prolog, the database will not be loaded at persistent_open.
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conc - (planned) concurrency, extends the locking for multiple readers/single writer locks
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trans - (planned) support for transactions (begin/commit/abort)
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Guides:
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- if the data mutates a lot, use [db,log].
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- if you mostly append data [log] suffices.
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- if the data is not important (can be regenerated) and mostly readonly then [db] is ok.
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- when using only [db] you must not forget to persistent_close!
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- for extra security against failures add [bak,sync].
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- don't use [bak] if you need to conserve disk space and the database is huge.
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- don't use [sync] if you need very fast writes.
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- turning all on [db,log,bak,sync] is probably the best, if you are undecided.
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- [ro,db] loads only the last saved db file.
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- [ro,log] loads the last saved db file if it exists and replays the log.
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- note that [ro] will fail if the db is not intact (.bak file present).
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(planned features)
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- [wo] is very limited and only useful if you want to log data to a file
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- [wo,db] will replay the log at close
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- [conc] is useful for shareing data between prolog processes, but this is not a
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high performance solution.
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- [trans] can improve performance of concurrent access somewhat
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*/
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persistent_open(PredDesc, File, Opts) :-
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module_goal(PredDesc, Module:Functor/Arity),
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atom(Functor), integer(Arity), atom(File),
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\+ persistent_desc(Module:Functor/Arity,_),
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atom_concat(File,'.db',DBfile),
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assertz(persistent_desc(Module:Functor/Arity,dbfile(DBfile))),
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atom_concat(File,'.bak',Backupfile),
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assertz(persistent_desc(Module:Functor/Arity,backupfile(Backupfile))),
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atom_concat(File,'.log',Logfile),
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assertz(persistent_desc(Module:Functor/Arity,logfile(Logfile))),
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system:pid(Pid),
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assertz(persistent_desc(Module:Functor/Arity,pid(Pid))),
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number_atom(Pid,P),
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atom_concat(Logfile,P,Mylogfile),
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assertz(persistent_desc(Module:Functor/Arity,mylogfile(Mylogfile))),
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atom_concat(File,'.lock',Lockfile),
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assertz(persistent_desc(Module:Functor/Arity,lockfile(Lockfile))),
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persistent_opts_store(Module:Functor/Arity,Opts),
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persistent_load(Module:Functor/Arity),
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( \+ persistent_desc(Module:Functor/Arity, ro), persistent_desc(Module:Functor/Arity, log)
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-> open(Logfile, append, Log),
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assertz(persistent_desc(Module:Functor/Arity,logstream(Log)))
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; true
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).
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/*
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closes the database associated with PredDesc ([Module:]Functor/Arity)
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*/
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persistent_close(PredDesc0) :-
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module_goal(PredDesc0,PredDesc),
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( persistent_desc(PredDesc, logstream(Log))
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-> close(Log)
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; true
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),
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persistent_save(PredDesc),
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persistent_desc(PredDesc, backupfile(Backupfile)),
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(system:delete_file(Backupfile,[ignore]); true),
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persistent_lock_release(PredDesc),
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retractall(persistent_desc(PredDesc,_)).
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/*
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assert data to the database, this is always an assertz, if you need some ordering,
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then store some kind of key within your data.
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rules can be asserted too
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*/
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persistent_assert(Term) :-
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Term = (Head0 :- Body),
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module_goal(Head0, Module:Head),
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functor(Head, Functor, Arity),
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once(persistent_desc(Module:Functor/Arity,_)),!,
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( persistent_desc(Module:Functor/Arity, logstream(Log))
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-> writeq(Log,+(((Module:Head):-Body))), write(Log,'.\n'),
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( persistent_desc(Module:Functor/Arity, sync)
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-> flush_output(Log)
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; true
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)
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; true
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),
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assertz((Module:Head:-Body)).
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persistent_assert(Term0) :-
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module_goal(Term0, Module:Term),
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functor(Term,Functor,Arity),
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once(persistent_desc(Module:Functor/Arity,_)),!,
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( persistent_desc(Module:Functor/Arity,logstream(Log))
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-> writeq(Log,+(Module:Term)), write(Log,'.\n'),
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( persistent_desc(Module:Functor/Arity, sync)
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-> flush_output(Log)
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; true
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)
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; true
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),
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assertz(Module:Term).
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/*
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retract a persistent Term
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*/
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persistent_retract(Term0) :-
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module_goal(Term0, Module:Term),
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functor(Term,Functor,Arity),
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once(persistent_desc(Module:Functor/Arity,_)),!,
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retract(Module:Term),
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( persistent_desc(Module:Functor/Arity, logstream(Log))
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-> writeq(Log,-(Module:Term)), write(Log,'.\n'),
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( persistent_desc(Module:Functor/Arity, sync)
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-> flush_output(Log)
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; true
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)
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; true
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).
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% transaction support for future
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persistent_begin.
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persistent_commit.
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persistent_abort.
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/*
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PRIVATE PREDICATES, DONT USE THESE
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*/
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% save all data to a .db file
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persistent_save(PredDesc) :-
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\+ persistent_desc(PredDesc,ro),
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( persistent_desc(PredDesc,db)
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-> persistent_desc(PredDesc,dbfile(DBfile)),
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(
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persistent_desc(PredDesc,bak)
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-> persistent_desc(PredDesc,backupfile(Backupfile)),
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( system:file_exists(DBfile)
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-> system:rename_file(DBfile,Backupfile)
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; true
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)
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; true
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),
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open(DBfile, write, S),
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persistent_writeall(PredDesc,S),
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close(S),
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persistent_desc(PredDesc,logfile(Logfile)),
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(system:delete_file(Logfile,[ignore]); true)
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; true
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).
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% write all predicates matching Functor/Arity to stream S
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persistent_writeall(PredDesc, S) :-
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module_goal(PredDesc, Module:Functor/Arity),
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functor(Clause, Functor, Arity),
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clause(Module:Clause, Body),
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( Body = true
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-> writeq(S,Module:Clause)
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; writeq(S,(Module:Clause:-Body))
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),
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write(S,'.\n'),
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fail.
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persistent_writeall(_,_).
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% load a database, recover logfile, recreate .db
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persistent_load(PredDesc) :-
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persistent_desc(PredDesc,dbfile(DBfile)),
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persistent_desc(PredDesc,backupfile(Backupfile)),
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persistent_desc(PredDesc,logfile(Logfile)),
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( persistent_desc(PredDesc,ro)
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-> \+ system:file_exists(Backupfile),
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( system:file_exists(DBfile)
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-> persistent_load_file(DBfile)
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; true
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),
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( persistent_desc(PredDesc,log), system:file_exists(Logfile)
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-> persistent_load_file(Logfile)
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; true
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)
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;
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persistent_lock_exclusive(PredDesc),
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( system:file_exists(Backupfile)
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-> system:rename_file(Backupfile, DBfile)
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; true
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),
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( system:file_exists(DBfile)
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-> persistent_load_file(DBfile)
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; true
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),
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( system:file_exists(Logfile)
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-> persistent_load_file(Logfile),
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( persistent_desc(PredDesc, db)
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-> persistent_save(PredDesc)
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; true
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)
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; true
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)
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).
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% load a .db file or replay a .log file
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persistent_load_file(File) :-
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open(File, read, S),
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repeat,
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read(S, TermIn),
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(
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TermIn == end_of_file,
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close(S),
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!
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;
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(
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TermIn = +(Term),
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assertz(Term)
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;
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TermIn = -(Term),
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retract(Term)
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;
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assertz(TermIn)
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),
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fail
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).
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%lock handling, so far only exclusive locks
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persistent_lock_exclusive(PredDesc) :-
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persistent_desc(PredDesc,lockfile(Lockfile)),
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persistent_desc(PredDesc,pid(Pid)),
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open(Lockfile, append, Lockappend),
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write(Lockappend,lock(write,Pid)),write(Lockappend,'.\n'),
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close(Lockappend),
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open(Lockfile, read, Lockread),
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read(Lockread,LPid),
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close(Lockread),
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LPid = lock(_,Pid).
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% recover lock
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persistent_lock_exclusive(PredDesc) :-
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persistent_desc(PredDesc, lockfile(Lockfile)),
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open(Lockfile, read, Lockread),
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read(Lockread,lock(_,LPid)),
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close(Lockread),
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\+ catch(kill(LPid,0),_,fail),
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(system:delete_file(Lockfile,[ignore]); true),
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%system:sleep(1),
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persistent_lock_exclusive(PredDesc).
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persistent_lock_release(PredDesc) :-
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persistent_lock_exclusive(PredDesc),
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persistent_desc(PredDesc,lockfile(Lockfile)),
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(system:delete_file(Lockfile,[ignore]); true).
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persistent_opts_store(_,[]).
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persistent_opts_store(PredDesc,[H|T]) :-
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assertz(persistent_desc(PredDesc,H)),
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persistent_opts_store(PredDesc,T).
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module_goal(Module:Goal,Module:Goal) :-
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callable(Goal), nonvar(Module),!.
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module_goal(Goal,Module:Goal) :-
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callable(Goal), prolog_flag(typein_module,Module).
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