org.jgroups.blocks

Class DistributedHashtable

public class DistributedHashtable extends Hashtable implements MessageListener, MembershipListener

Provides the abstraction of a java.util.Hashtable that is replicated at several locations. Any change to the hashtable (clear, put, remove etc) will transparently be propagated to all replicas in the group. All read-only methods will always access the local replica.

Both keys and values added to the hashtable must be serializable, the reason being that they will be sent across the network to all replicas of the group. Having said this, it is now for example possible to add RMI remote objects to the hashtable as they are derived from java.rmi.server.RemoteObject which in turn is serializable. This allows to lookup shared distributed objects by their name and invoke methods on them, regardless of one's onw location. A DistributedHashtable thus allows to implement a distributed naming service in just a couple of lines.

An instance of this class will contact an existing member of the group to fetch its initial state (using the state exchange funclet StateExchangeFunclet.

Version: $Id: DistributedHashtable.java,v 1.20 2005/11/10 20:54:01 belaban Exp $

Author: Bela Ban Alfonso Olias-Sanz

Nested Class Summary
interfaceDistributedHashtable.Notification
Field Summary
protected RpcDispatcherdisp
protected Loglog
protected Promisestate_promise
Constructor Summary
DistributedHashtable(String groupname, ChannelFactory factory, String properties, long state_timeout)
Creates a DistributedHashtable
DistributedHashtable(String groupname, ChannelFactory factory, String properties, boolean persistent, long state_timeout)
Creates a DisttributedHashtable.
DistributedHashtable(JChannel channel, long state_timeout)
DistributedHashtable(JChannel channel, boolean persistent, long state_timeout)
DistributedHashtable(PullPushAdapter adapter, Serializable id, long state_timeout)
Uses a user-provided PullPushAdapter to create the dispatcher rather than a Channel.
DistributedHashtable(PullPushAdapter adapter, Serializable id)
Method Summary
voidaddNotifier(DistributedHashtable.Notification n)
voidblock()
Block sending and receiving of messages until ViewAccepted is called
voidclear()
Clears this hashtable so that it contains no keys
ChannelgetChannel()
StringgetGroupName()
AddressgetLocalAddress()
booleangetPersistent()
byte[]getState()
protected voidinit(long state_timeout)
static voidmain(String[] args)
Objectput(Object key, Object value)
Maps the specified key to the specified value in the hashtable.
voidputAll(Map m)
Copies all of the mappings from the specified Map to this Hashtable These mappings will replace any mappings that this Hashtable had for any of the keys currently in the specified Map.
voidreceive(Message msg)
Objectremove(Object key)
Removes the key (and its corresponding value) from the Hashtable.
voidremoveNotifier(DistributedHashtable.Notification n)
voidsetPersistent(boolean p)
voidsetState(byte[] new_state)
voidstart(long state_timeout)
Fetches the state
voidstop()
voidsuspect(Address suspected_mbr)
Called when a member is suspected
voidviewAccepted(View new_view)
void_clear()
Object_put(Object key, Object value)
void_putAll(Map m)
Object_remove(Object key)

Field Detail

disp

protected transient RpcDispatcher disp

log

protected final Log log

state_promise

protected final transient Promise state_promise

Constructor Detail

DistributedHashtable

public DistributedHashtable(String groupname, ChannelFactory factory, String properties, long state_timeout)
Creates a DistributedHashtable

Parameters: groupname The name of the group to join factory The ChannelFactory which will be used to create a channel properties The property string to be used to define the channel state_timeout The time to wait until state is retrieved in milliseconds. A value of 0 means wait forever.

DistributedHashtable

public DistributedHashtable(String groupname, ChannelFactory factory, String properties, boolean persistent, long state_timeout)
Creates a DisttributedHashtable. Optionally the contents can be saved to persistemt storage using the PersistenceManager.

Parameters: groupname Name of the group to join factory Instance of a ChannelFactory to create the channel properties Protocol stack properties persistent Whether the contents should be persisted state_timeout Max number of milliseconds to wait until state is retrieved

DistributedHashtable

public DistributedHashtable(JChannel channel, long state_timeout)

DistributedHashtable

public DistributedHashtable(JChannel channel, boolean persistent, long state_timeout)

DistributedHashtable

public DistributedHashtable(PullPushAdapter adapter, Serializable id, long state_timeout)
Uses a user-provided PullPushAdapter to create the dispatcher rather than a Channel. If id is non-null, it will be used to register under that id. This is typically used when another building block is already using PullPushAdapter, and we want to add this building block in addition. The id is the used to discriminate between messages for the various blocks on top of PullPushAdapter. If null, we will assume we are the first block created on PullPushAdapter.

Parameters: adapter The PullPushAdapter which to use as underlying transport id A serializable object (e.g. an Integer) used to discriminate (multiplex/demultiplex) between requests/responses for different building blocks on top of PullPushAdapter. state_timeout Max number of milliseconds to wait until state is retrieved

DistributedHashtable

public DistributedHashtable(PullPushAdapter adapter, Serializable id)

Method Detail

addNotifier

public void addNotifier(DistributedHashtable.Notification n)

block

public void block()
Block sending and receiving of messages until ViewAccepted is called

clear

public void clear()
Clears this hashtable so that it contains no keys

getChannel

public Channel getChannel()

getGroupName

public String getGroupName()

getLocalAddress

public Address getLocalAddress()

getPersistent

public boolean getPersistent()

getState

public byte[] getState()

init

protected void init(long state_timeout)

main

public static void main(String[] args)

put

public Object put(Object key, Object value)
Maps the specified key to the specified value in the hashtable. Neither of both parameters can be null

Parameters: key - the hashtable key value - the value

Returns: the previous value of the specified key in this hashtable, or null if it did not have one

putAll

public void putAll(Map m)
Copies all of the mappings from the specified Map to this Hashtable These mappings will replace any mappings that this Hashtable had for any of the keys currently in the specified Map.

Parameters: m - Mappings to be stored in this map

receive

public void receive(Message msg)

remove

public Object remove(Object key)
Removes the key (and its corresponding value) from the Hashtable.

Parameters: key - the key to be removed.

Returns: the value to which the key had been mapped in this hashtable, or null if the key did not have a mapping.

removeNotifier

public void removeNotifier(DistributedHashtable.Notification n)

setPersistent

public void setPersistent(boolean p)

setState

public void setState(byte[] new_state)

start

public void start(long state_timeout)
Fetches the state

Parameters: state_timeout

Throws: ChannelClosedException ChannelNotConnectedException

stop

public void stop()

suspect

public void suspect(Address suspected_mbr)
Called when a member is suspected

viewAccepted

public void viewAccepted(View new_view)

_clear

public void _clear()

_put

public Object _put(Object key, Object value)

_putAll

public void _putAll(Map m)

See Also: java.util.Map#putAll(java.util.Map)

_remove

public Object _remove(Object key)
Copyright ? 1998-2005 Bela Ban. All Rights Reserved.