January 2006


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Sean Luke <[log in to unmask]>
Reply To:
ECJ Evolutionary Computation Toolkit <[log in to unmask]>
Fri, 20 Jan 2006 01:22:39 -0500
text/plain (168 lines)
So some explanation.

ECJ's new code (which I personally wrote a few months  
back :-) has the additional wrinkle of a jobs facility because so  
many people asked for one.  The problem is how to start up from  
checkpoint and continue right at the job number you had done before.   
That's where it's a little complicated, but not too bad.

A simpler, job-free main, would go something like this (I'm doing  
this at 12:30 PM so pardon me if I screw up somewhere!)

	state = possiblyRestoreFromCheckpoint(args);
	if (state!=null)  // meaning we loaded from checkpoint;
		parameters = loadParameterDatabase(args);
		state = initialize(parameters, 0);  // no job offset
		startFresh(state, null);  // no job prefix

All the job stuff proceeds from there.

The way we're doing jobs is that ECJ maintains an Object[array] in called "job".  You can use this array for  
whatever you want if you're writing your own main().  Or you can, in  
the example above, not use it at all.  The purpose of the array is to  
enable you to store your job information and have it survive  
checkpoints and restores.  There is another variable in  
EvolutionState also called "runtimeArguments", which is the array of  
strings passed in as args[] originally to main().  Because jobs might  
need that info to survive too.

The basic main() we have is very simple -- it just increments a  
single job number, starting at 0.  We store the number as an Integer  
in jobs[0].  So here's some explanation of the code.  Keep in mind  
this is the DEFAULT main().  ECJ has been carefully arranged so that  
you can do your own main loop in any way you like.

1. We first try to load the state from a checkpoint if there was  
one.  If so, we finish that run.

         state = possiblyRestoreFromCheckpoint(args);
         if (state!=null)

2. Okay, that job is finished if it existed.  Now, we make the job  
number 0 if we're starting from the very beginning (not from  
checkpoint), but if we had loaded from checkpoint, we want to set the  
new job number to the old job number (stored away in job[0]) plus 1.

         int jobCurrent = 0;
         if (state != null)
                 if (state.runtimeArguments == null)
                 args = state.runtimeArguments;
                 jobCurrent = ((Integer)(state.job[0])).intValue() + 1;
             catch (Exception e)

3.  Now we load the parameter database.  Here's where the confusion  
comes in.  We're loading the parameter database every job in our  
simple main().  Why do we do this?  Mostly because parameter  
databases can get modified at runtime by the experimenter.  Otherwise  
there's not much reason I think.  The ParameterDatabase has a File  
called "directory" which might be problematic if it's restored from  
checkpoint, and a Vector called listeners, but I don't think either  
is probably a problem in most cases.  So sure, you could try just  
loading the parameter database only if we're starting fresh, and  
reusing the database in other cases.  I was throwing away the old  
database and reloading it because it was cleaner and less likely to  
generate experimenter-tickled bugs.

         parameters = loadParameterDatabase(args);
         int numJobs = parameters.getIntWithDefault(new Parameter 
("jobs"), null, 1);
         if (numJobs < 1)

4. Now we just loop through the jobs. Each time we reload the  
parameter database if necessary, then initialize the EvolutionState  
from the database (this calls all the setup() methods, and the random  
number generators, more or less.  The RNG's seeds are incremented  
using the job# perhaps).  Then we stash away the job number in the  
EvolutionState in case it's going to get checkpointed out.  We also  
figure out the prefix that the job should use to make filenames  
specific to that job so jobs don't write on each other's output  
files.  If only one job, we don't use a prefix (for backwards  
compatibility).  And then we start the run with startFresh!  Then  
trash the parameters:

         for(int job = jobCurrent ; job < numJobs; job++)
             if (parameters == null)
                 parameters = loadParameterDatabase(args);

             state = initialize(parameters, job);
             state.output.systemMessage("Job: " + job);
             state.job = new Object[1];
             state.job[0] = new Integer(job);
             state.runtimeArguments = args;

             String jobFilePrefix = null;
             if (numJobs > 1)
                 jobFilePrefix = "job." + job + ".";

             startFresh(state, jobFilePrefix);
             parameters = null;

5. And then we quit.


In truth, you don't have to follow this scheme at all; you can setup  
and pulse EvolutionState any way you like.  Here's the general  

A. If starting up from checkpoint, call  
	which does a bunch of stuff for you.
B. Else you need to make a parameter database and set up various things:
	1. The Output and logs for stdout, stderr, etc.
	2. The random number generators
	3. The evolutionState, and set some variables in it
	[All this is done by Evolve.initialize if you want to use that instead]
	4. if (jobFilePrefix != null)
	5. state.startFresh()
C. Now you have a functioning EvolutionState.  Repeatedly call
	result = state.evolve();
	... until result = EvolutionState.R_NOTDONE
D. state.finish(result)
E. state.output.flush()
F. print out the used parameters etc. if you wish (See  
Evolve.startFresh(...) for code)
G. If you're all done, flush various streams and close the Output,  
and exit(0)

And you don't even have to load a parameter database from a file --  
you can construct one by hand if you like.

But in explaining this on this email I see an ugliness I didn't clean  
up.  I use to finish out the checkpointed run, but I  
use startFresh(...) to do a noncheckpointed run.  startFresh(...)  
does a bunch of items, including the same basic code as 
(...).  But they're [1] not orthogonal and [2] startFresh cleans up  
afterwards and dumps parameters but it looks like my main(...) code  
does *not* do that if restoring from checkpoint.  Not a big bug, but  
I should make that prettier.  Thanks guys, even if inadvertently!