ec.exchange
Class IslandExchange

java.lang.Object
  extended by ec.Exchanger
      extended by ec.exchange.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 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 emigrants 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 emigrants only after generation 6, and then sends emigrants on every 4 generations beyond that. The purpose for the start times and modulos is so that not every client sends emigrants 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.start
bool = true or false (default)
server: (Only if island model is synchronous) The generation when islands begin sending emigrants.
base.mod
bool = true or false (default)
server: (Only if island model is synchronous) The number of generations islands wait between sending emigrants.
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 emigrants to.
base.island.n.mig.m
int >= 1
server: The ID of island #m that island #n sends emigrants to.
base.island.n.size
int >= 1
server: The number of emigrants (per subpopulation) that island #n sends to other islands.
base.island.n.start
int >= 0
server: The generation when island #n begins sending emigrants.
base.island.n.mod
int >= 1
server: The number of generations that island #n waits between sending emigrants.
base.island.n.mailbox-capacity
int >= 1
server: The maximum size (per subpopulation) of the mailbox for island #n.

Parameter bases

base.select selection method for the client's migrants

Version:
2.0
Author:
Liviu Panait & Sean Luke
See Also:
Serialized Form

Field Summary
 Parameter base
          My parameter base -- I need to keep this in order to help the server reinitialize contacts
 int clientPort
          The port of the client mailbox
 boolean compressedCommunication
          whether the communication is compressed or not
static java.lang.String FOUND
          Found signal
static int FOUND_TIMEOUT
          How long we sleep between checking for FOUND messages
 boolean iAmServer
          whether the server should be running on the current island or not
 SelectionMethod immigrantsSelectionMethod
          the selection method for emigrants
 SelectionMethod indsToDieSelectionMethod
          the selection method for individuals to be replaced by immigrants
 int modulo
          how often to send individuals
 int offset
          after how many generations to start sending individuals
static java.lang.String OKAY
          Okay signal
 java.lang.String ownId
          the id of the current island
static java.lang.String P_CHATTY
          Whether or not we're chatty
static java.lang.String P_CLIENT_PORT
          The client port
static java.lang.String P_COMPRESSED_COMMUNICATION
          Whether the communication is compressed or not
static java.lang.String P_IS_SERVER
          Whether the server is also on this island
static java.lang.String P_OWN_ID
          The id of the island
static java.lang.String P_SELECT_METHOD
          The selection method for sending individuals to other islands
static java.lang.String P_SELECT_TO_DIE_METHOD
          The selection method for deciding individuals to be replaced by immigrants
static java.lang.String P_SERVER_ADDRESS
          The server address
static java.lang.String P_SERVER_PORT
          The server port
 java.lang.String serverAddress
          The address of the server
 int serverPort
          The port of the server
 java.lang.Thread serverThread
          The thread of the server (is different than null only for the island with the server)
 int size
          how many individuals to send each time
static int SLEEP_TIME
          How long we sleep in between attempts to connect or look for signals
static java.lang.String SYNC
          Synchronize signal
 boolean synchronous
          synchronous or asynchronous communication
 
Constructor Summary
IslandExchange()
           
 
Method Summary
 void closeContacts(EvolutionState state, int result)
          Closes contacts with other processes, if that's what you're doing.
 int evolve()
           
 void finish(int result)
           
 void fireUpServer(EvolutionState state, Parameter serverBase)
          Fires up the server.
 void initializeContacts(EvolutionState state)
          Initializes contacts with other processes, if that's what you're doing.
static void main(java.lang.String[] args)
           
 Population postBreedingExchangePopulation(EvolutionState state)
          Performs exchanges after the population has been bred but before it has been evaluated, once every generation (or pseudogeneration).
 Population preBreedingExchangePopulation(EvolutionState state)
          Performs exchanges after the population has been evaluated but before it has been bred, once every generation (or pseudogeneration).
 void reinitializeContacts(EvolutionState state)
          Initializes contacts with other processes, if that's what you're doing.
 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).
 void setup(EvolutionState state, Parameter _base)
          Sets up the object by reading it from the parameters stored in state, built off of the parameter base base.
 void startFresh()
           
 void startFromCheckpoint()
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

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

OKAY

public static final java.lang.String OKAY
Okay signal

See Also:
Constant Field Values

SYNC

public static final java.lang.String SYNC
Synchronize signal

See Also:
Constant Field Values

FOUND

public static final java.lang.String FOUND
Found signal

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 emigrants


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

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.


fireUpServer

public void fireUpServer(EvolutionState state,
                         Parameter serverBase)
Fires up the server.


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.

Specified by:
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.

Specified by:
reinitializeContacts in class Exchanger

preBreedingExchangePopulation

public Population preBreedingExchangePopulation(EvolutionState state)
Description copied from class: Exchanger
Performs exchanges after the population has been evaluated but before it has been bred, once every generation (or pseudogeneration).

Specified by:
preBreedingExchangePopulation in class Exchanger

postBreedingExchangePopulation

public Population postBreedingExchangePopulation(EvolutionState state)
Description copied from class: Exchanger
Performs exchanges after the population has been bred but before it has been evaluated, once every generation (or pseudogeneration).

Specified by:
postBreedingExchangePopulation 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.

Specified by:
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