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Simulate IBM's Advanced Job Scheduler in Common Lisp
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README.md

ajsm.lisp --- IBM i Advanced Job Scheduler Simulator

[Note: It's a simulator, not a model. A simulation IMPLEMENTS a model. So, I changed the name of the repository, but haven't changed the file names.]

ajsm.lisp provides a model of a subset of IBM's Advanced Job Scheduler for the IBM i system -- namely, the subset which I actually use. The threshold function is not modeled. It is not modeled because I don't use it. I don't use it because neither I nor IBM knows what it does nor how it works nor what is it is for. Other than that, it seems to work.

Of course, the cardinality of the set which is the intersection of the set of people who use AJS and the set of people who are comfortable using Common Lisp is probably one -- or, in the Queen's English, I'm probably the only one who would ever use this thing. But you never know, so I am putting it online.

Purpose

The purpose is to test job schedules (timing, dependencies, and so forth) in advance of actually implementing them on a live system. It is possible to simulate other job schedulers with it -- in particular the IBM i built in "WRKJOBSCDE" scheduler is easy to model with this system, because it's functionality is basically a subset of AJS's functionality. In fact, you can model WRKJOBSCDE jobs and AJS jobs at the same time. Just add the job definitions and they all run together.

Requirements

ajsm.lisp is pretty simple and should run on any conforming Common Lisp implementation.

If you would like to use the functions that export your graph (the graph of scheduled jobs) to the Graphviz .dot format and render them then naturally you will need Graphviz installed as well. This functionality requires Common Lisp libraries s-dot and trivial-shell. These are loaded right at the top of ajsm.lisp using Quicklisp.

So, to recap, if you have Graphviz and Quicklisp installed, then you are ready to go. If you are missing either of those, then you will want to comment out those two (ql:quickload... lines.

Installation

After seeing the previous section, load the file in your Common Lisp implementation. Ta-da!

Use

Take a look at example-schedule.lisp. It loads ajsm.lisp, so you can just load that file and you will be in the ajsm package and ready to run the simulation.

A set of jobs is a directed graph. The vertices are all Boolean values. They may represent a job which must run, or a job which must run before another job runs; they may represent a time of day which it must be for a job to run, or a day of the week, or a complex calendar which must in effect say, "yes, you can run today." Mind, now -- they are ALL just vertices on the graph.

The simulation simply cycles through all the nodes on the graph, and for each node, checks to see if all the nodes which lead to it are set to a Boolean true value. If so, it sets that node to true. "Setting it to true" is the same thing is "running" the job. Once the job has "run" then it is "true" for the purposes of any and all nodes (jobs) which depend on it. Make sense?

(So as it happens, there is a facility which allows you to actually run arbitrary Lisp code when a "job" (i.e., a vertex) is "run" (i.e., set TRUE). So, using that, you could actually use the model of a job scheduler as a real job scheduler -- but you would have to write some code to hook it into some kind of clock to actually use it for realz.)

So the questions are basically two, then: 1) how do you define a schedule, and 2) how do you run through it.

How to define a job schedule

Well, first, check example-schedule.lisp and take a look at how jobs are defined. Then look at the code in ajsm.lisp because there are some comments, some doc strings, and more importantly, comments above most of the functions and macros which have examples of the syntax. Personally I find that helpful.

How to run the simulation

Well, first, check example-schedule.lisp and run function `example-do-december-2012' and you will see a run.

Export to Graphviz format

You can export your graph to Graphviz' .dot format and from there render it as a .pdf or .tiff file or whatever you like to visualize it. Now that's sort of fun, isn't it?

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