Documentation of 'ec.exchange.IslandExchange' Java class
IslandExchange
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ec.exchange

Class IslandExchange

  • All Implemented Interfaces:
    Setup, Singleton, java.io.Serializable

    public class IslandExchange
extends Exchanger
    IslandExchange is an Exchanger which implements a simple but quite functional asynchronous island model for doing massive parallel distribution of evolution across beowulf clusters. One of its really nice features is that because everything is in Java, your cluster can have mixed platforms in it (MacOS, Unix, Windoze, whatever you like). You can also have multiple processes running on the same machine, as long as they're given different client ports. IslandExchange operates over TCP/IP with Java sockets, and is compatible with checkpointing.

    IslandExchange uses an arbitrary graph topology for migrating individuals from island (EC process) to island over the network. There are a few restrictions for simplicity, however:

    • Every island must have the same kind of subpopulations and species.
    • Every subpopulation will send the same number of migrants as any other subpopulation.
    • Migrants from a subpopulation will go to the same subpopulation.

    Every island is a client. Additionally one island is designated a server. Note that, just like in the Hair Club for Men, the server is also a client. The purpose of the server is to synchronize the clients so that they all get set up properly and hook up to each other, then to send them small signal messages (like informing them that another client has discovered the ideal individual), and help them gracefully shut down. Other than these few signals which are routed through the server to the clients, all other information -- namely the migrants themselves -- are sent directly from client to client in a peer-to-peer fashion.

    The topology of the network is stored solely in the server's parameter database. When the clients fire up, they first set up "Mailboxes" (where immigrants from other clients will appear), then they go to the server and ask it who they should connect to to send migrants. The server tells them, and then they then hook up. When a client has finished hooking up, it reports this to the server. After everyone has hooked up, the server tells the clients to begin evolution, and they're off and running.

    Islands send immigrants to other islands by copying good individuals (selected with a SelectionMethod) and sending the good individuals to the mailboxes of receiving clients. Once an individual has been received, it is considered to be unevaluated by the receiving island, even though it had been previously evaluated by the sending island.

    The IslandExchange model is typically asynchronous because migrants may appear in your mailbox at any time; islands do not wait for each other to complete the next generation. This is a more efficient usage of network bandwidth. When an island completes its breeding, it looks inside its mailbox for new migrants. It then replaces some of its newly-bred individuals (chosen entirely at random) with the migrants (we could have increased the population size so we didn't waste that breeding time, but we were lazy). It then flushes the mailbox, which patiently sits waiting for more individuals.

    Clients may also be given different start times and modulos for migrating. For example, client A might be told that he begins sending immigrants only after generation 6, and then sends immigrants on every 4 generations beyond that. The purpose for the start times and modulos is so that not every client sends immigrants at the same time; this also makes better use of network bandwidth.

    When a client goes down, the other clients deal with it gracefully; they simply stop trying to send to it. But if the server goes down, the clients do not continue operation; they will shut themselves down. This means that in general you can shut down an entire island model network just by killing the server process. However, if the server quits because it runs out of generations, it will wait for the clients to all quit before it finally stops.

    IslandExchange works correctly with checkpointing. If you restart from a checkpoint, the IslandExchange will start up the clients and servers again and reconnect. Processes can start from different checkpoints, of course. However, realize that if you restart from a checkpoint, some migrants may have been lost in transit from island to island. That's the nature of networking without heavy-duty transaction management! This means that we cannot guarantee that restarting from checkpoint will yield the same results as the first run yielded.

    Islands are not described in the topology parameters by their IP addresses; instead, they are described by "ids", strings which uniquely identify each island. For example, "gilligans-island" might be an id. :-) This allows you to move your topology to different IP addresses without having to change all your parameter files! You can even move your topology to totally different machines, and restart from previous checkpoints, and everything should still work correctly.

    There are times, especially to experiment with dynamics, that you need a synchronous island model. If you specify synchronicity, the server's stated modulo and offset override any modulii or offsets specified by clients. Everyone will use the server's modulo and offset. This means that everyone will trade individuals on the same generation. Additionally, clients will wait until everyone else has traded, before they are permitted to continue evolving. This has the effect of locking all the clients together generation-wise; no clients can run faster than any other clients.

    One last item: normally in this model, the server is also a client. But if for some reason you need the server to be a process all by itself, without creating a client as well, you can do that. You spawn such a server differently than the main execution of ECJ. To spawn a server on a given server params file (let's say it's server.params) but NOT spawn a client, you do: 

     java ec.exchange.IslandExchange -file server.params

    ...this sets up a special process which just spawns a server, and doesn't do all the setup of an evolutionary run. Of course as usual, for each of the clients, you'll run java ec.Evolve ... instead.

    Parameters

    Note: some of these parameters are only necessary for creating clients. Others are necessary for creating the server.

    base.chatty
    boolean, default = true    		 Should we be verbose or silent about our exchanges?
    base.select
    classname, inherits and != ec.SelectionMethod    		 client: The selection method used for picking migrants to emigrate to other islands
    base.select-to-die
    classname, inherits and != ec.SelectionMethod, default is ec.select.RandomSelection    		 client: The selection method used for picking individuals to be replaced by incoming migrants. IMPORTANT Note. This selection method must not pick an individual based on fitness. The selection method will be called just after breeding but before evaluation; many individuals will not have had a fitness assigned at that point. You might want to design a SelectionMethod other than RandomSelection, however, to do things like not picking elites to die.
    base.server-addr
    String    		 client: The IP address of the server
    base.server-port
    int >= 1    		 client: The port number of the server
    base.client-port
    int >= 1    		 client: The port number of the client (where it will receive migrants) -- this should be different from the server port.
    base.id
    String    		 client: The "name" the client is giving itself. Each client should have a unique name. For example, "gilligans-island".
    base.compressed
    bool = true (default) or false    		 client: Whether the communication with other islands should be compressed or not. Compressing uses more CPU, but it may also significantly reduce communication.
    base.i-am-server
    bool = true or false (default)    		 client: Is this client also the server? If so, it'll read the server parameters and set up a server as well.
    base.sync
    bool = true or false (default)    		 server: Are we doing a synchronous island model? If so, the server's modulo and offset override any client's stated modulo and offset.
    base.num-islands
    int >= 1    		 server: The number of islands in the topology.
    base.island.n.id
    String    		 server: The ID of island #n in the topology.
    base.island.n.num-mig
    int >= 1    		 server: The number of islands that island #n sends immigrants to.
    base.island.n.mig.m
    int >= 1    		 server: The ID of island #m that island #n sends immigrants to.
    base.island.n.size
    int >= 1    		 server: The number of immigrants (per subpopulation) that island #n sends to other islands. If not set, uses the default parameter below.
    base.size
    int >= 1    		 server: Default parameter: number of immigrants (per subpopulation) that a given island sends to other islands.
    base.island.n.start
    int >= 0    		 server: The generation when island #n begins sending immigrants. If not set, uses the default parameter below.
    base.start
    bool = true or false (default)    		 server: Default parameter: the generation when an island begins sending immigrants.
    base.island.n.mod
    int >= 1    		 server: The number of generations that island #n waits between sending immigrants. If not set, uses the default parameter below.
    base.mod
    bool = true or false (default)    		 server: Default parameter: The number of generations an island waits between sending immigrants.
    base.island.n.mailbox-capacity
    int >= 1    		 server: The maximum size (per subpopulation) of the mailbox for island #n. If not set, uses the default parameter below.
    base.mailbox-capacity
    int >= 1    		 server: Default parameter: the maximum size (per subpopulation) of the mailbox for a given island.

    Parameter bases

    base.select selection method for the client's migrants
    See Also:
    Serialized Form

    • Field Detail

      • P_SERVER_ADDRESS

        public static final java.lang.String P_SERVER_ADDRESS
        The server address
        See Also:
        Constant Field Values

      • P_SERVER_PORT

        public static final java.lang.String P_SERVER_PORT
        The server port
        See Also:
        Constant Field Values

      • P_CLIENT_PORT

        public static final java.lang.String P_CLIENT_PORT
        The client port
        See Also:
        Constant Field Values

      • P_IS_SERVER

        public static final java.lang.String P_IS_SERVER
        Whether the server is also on this island
        See Also:
        Constant Field Values

      • P_OWN_ID

        public static final java.lang.String P_OWN_ID
        The id of the island
        See Also:
        Constant Field Values

      • P_COMPRESSED_COMMUNICATION

        public static final java.lang.String P_COMPRESSED_COMMUNICATION
        Whether the communication is compressed or not
        See Also:
        Constant Field Values

      • P_SELECT_METHOD

        public static final java.lang.String P_SELECT_METHOD
        The selection method for sending individuals to other islands
        See Also:
        Constant Field Values

      • P_SELECT_TO_DIE_METHOD

        public static final java.lang.String P_SELECT_TO_DIE_METHOD
        The selection method for deciding individuals to be replaced by immigrants
        See Also:
        Constant Field Values

      • SLEEP_TIME

        public static final int SLEEP_TIME
        How long we sleep in between attempts to connect or look for signals
        See Also:
        Constant Field Values

      • FOUND_TIMEOUT

        public static final int FOUND_TIMEOUT
        How long we sleep between checking for FOUND messages
        See Also:
        Constant Field Values

      • P_CHATTY

        public static final java.lang.String P_CHATTY
        Whether or not we're chatty
        See Also:
        Constant Field Values

      • serverThread

        public java.lang.Thread serverThread
        The thread of the server (is different than null only for the island with the server)

      • base

        public Parameter base
        My parameter base -- I need to keep this in order to help the server reinitialize contacts

      • serverAddress

        public java.lang.String serverAddress
        The address of the server

      • serverPort

        public int serverPort
        The port of the server

      • clientPort

        public int clientPort
        The port of the client mailbox

      • iAmServer

        public boolean iAmServer
        whether the server should be running on the current island or not

      • ownId

        public java.lang.String ownId
        the id of the current island

      • compressedCommunication

        public boolean compressedCommunication
        whether the communication is compressed or not

      • immigrantsSelectionMethod

        public SelectionMethod immigrantsSelectionMethod
        the selection method for immigrants

      • indsToDieSelectionMethod

        public SelectionMethod indsToDieSelectionMethod
        the selection method for individuals to be replaced by immigrants

      • synchronous

        public boolean synchronous
        synchronous or asynchronous communication

      • modulo

        public int modulo
        how often to send individuals

      • offset

        public int offset
        after how many generations to start sending individuals

      • size

        public int size
        how many individuals to send each time

      • outgoingIds

        public java.lang.String[] outgoingIds

    • Constructor Detail

      • IslandExchange

        public IslandExchange()

    • Method Detail

      • main

        public static void main(java.lang.String[] args)
                 throws java.lang.InterruptedException
        Throws:
        java.lang.InterruptedException

      • setup

        public void setup(EvolutionState state,
                  Parameter _base)
        Description copied from interface: Setup
        Sets up the object by reading it from the parameters stored in state, built off of the parameter base base. If an ancestor implements this method, be sure to call super.setup(state,base); before you do anything else.

      • initializeContacts

        public void initializeContacts(EvolutionState state)
        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.
        Overrides:
        initializeContacts in class Exchanger

      • reinitializeContacts

        public void reinitializeContacts(EvolutionState state)
        Initializes contacts with other processes, if that's what you're doing. Called after restarting from a checkpoint.
        Overrides:
        reinitializeContacts in class Exchanger

      • runComplete

        public java.lang.String runComplete(EvolutionState state)
        Called after preBreedingExchangePopulation(...) to evaluate whether or not the exchanger wishes the run to shut down (with ec.EvolutionState.R_FAILURE). 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. This function does not return a String as soon as it wants to exit (another island found the perfect individual, or couldn't connect to the server). Instead, it sets a flag, called message, to remember next time to exit. This is due to a need for a graceful shutdown, where checkpoints are working properly and save all needed information.
        Specified by:
        runComplete in class Exchanger

      • closeContacts

        public void closeContacts(EvolutionState state,
                          int result)
        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.
        Overrides:
        closeContacts in class Exchanger

      • finish

        public void finish(int result)

      • startFromCheckpoint

        public void startFromCheckpoint()

      • startFresh

        public void startFresh()

      • evolve

        public int evolve()
           throws java.lang.InternalError
        Throws:
        java.lang.InternalError
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