/*
  Copyright 2006 by Sean Luke
  Licensed under the Academic Free License version 3.0
  See the file "LICENSE" for more information
*/


package ec;

/* 
 * Exchanger.java
 * 
 * Created: Tue Aug 10 21:59:17 1999
 * By: Sean Luke
 */

/**
 * The Exchanger is a singleton object whose job is to (optionally)
 * perform individual exchanges between subpopulations in the run,
 * or exchange individuals with other concurrent evolutionary run processes,
 * using sockets or whatever.  Keep in mind that other processes may go down,
 * or be started up from checkpoints, etc.
 *
 * @author Sean Luke
 * @version 1.0 
 */

public abstract class Exchanger implements Singleton
    {
    private static final long serialVersionUID = 1;

    /** Initializes contacts with other processes, if that's what you're doing. Called at the beginning of an evolutionary run, before a population is set up. */
    public void initializeContacts(EvolutionState state) { }

    /** Initializes contacts with other processes, if that's what you're doing.  Called after restarting from a checkpoint. */
    public void reinitializeContacts(EvolutionState state) { }

    /** Performs exchanges after the population has been evaluated but before it has been bred,
        once every generation (or pseudogeneration). */
    public abstract Population preBreedingExchangePopulation(EvolutionState state);

    /** Performs exchanges after the population has been bred but before it has been evaluated,
        once every generation (or pseudogeneration). */
    public abstract Population postBreedingExchangePopulation(EvolutionState state);

    /** Typically called by preBreedingExchangePopulation prior to migrating an individual.
        Override this method to process the migrant, or provide a different Individual to migrate.
        The default simply returns the individual.  "island" refers to the island id of the
        destination island for this individual, or null if there is no island (as is the case
        in InterPopulationExchange).  "subpop" refers the expected subpopulation of the individual
        in the destination island, or the subpopulation the indivdiual is migrating to in InterPopulationExchange.
        Hint: if you are using IslandExchange and your island has access to the server exchange parameters 
        ("exch.num-islands" and all parameters starting with "exch.island."), you can can call
        IslandExchange.getIslandIndex(state, island) to retrieve the island number in the parameters,
        from which you can then determine additional useful information about the destination island. */
    protected Individual process(EvolutionState state, int thread, String island, int subpop, Individual ind)
        {
        return ind;
        }

    /** Called after preBreedingExchangePopulation(...) to evaluate whether or not
        the exchanger wishes the run to shut down (with ec.EvolutionState.R_FAILURE) --
        returns a String (which will be printed out as a message) if the exchanger
        wants to shut down, else returns null if the exchanger does NOT want to shut down.
        Why would you want to shut down?
        This would happen for two reasons.  First, another process might have found
        an ideal individual and the global run is now over.  Second, some network
        or operating system error may have occurred and the system needs to be shut
        down gracefully.  Note that if the exchanger wants to shut down, the system
        will shut down REGARDLESS of whether or not the user stated 
        ec.EvolutionState.quitOnRunComplete. */
    public abstract String runComplete(EvolutionState state);

    /** Closes contacts with other processes, if that's what you're doing.  Called at the end of an evolutionary run. result is either ec.EvolutionState.R_SUCCESS or ec.EvolutionState.R_FAILURE, indicating whether or not an ideal individual was found. */
    public void closeContacts(EvolutionState state, int result) { }
    }
