org.jgroups.blocks

Class DistributedHashtable

java.lang.Object

java.util.Dictionary

java.util.Hashtable

org.jgroups.blocks.DistributedHashtable

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.util.Map, MembershipListener, MessageListener

public class DistributedHashtable
extends java.util.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 1.26.2.2 2007/04/26 16:43:00 vlada Exp $

Author:

Bela Ban, Alfonso Olias-Sanz

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	DistributedHashtable.Notification

Field Summary

Fields

Modifier and Type	Field and Description
protected RpcDispatcher	disp
protected org.apache.commons.logging.Log	log
protected Promise	state_promise

Constructor Summary

Constructors

Constructor and Description
DistributedHashtable(Channel channel, boolean persistent, long state_timeout)
DistributedHashtable(Channel channel, long state_timeout)
DistributedHashtable(PullPushAdapter adapter, java.io.Serializable id)
DistributedHashtable(PullPushAdapter adapter, java.io.Serializable id, long state_timeout) Uses a user-provided PullPushAdapter to create the dispatcher rather than a Channel.
DistributedHashtable(java.lang.String groupname, ChannelFactory factory, java.lang.String properties, boolean persistent, long state_timeout) Creates a DisttributedHashtable.
DistributedHashtable(java.lang.String groupname, ChannelFactory factory, java.lang.String properties, long state_timeout) Creates a DistributedHashtable

Method Summary

Methods

Modifier and Type	Method and Description
void	_clear()
java.lang.Object	_put(java.lang.Object key, java.lang.Object value)
void	_putAll(java.util.Map m)
java.lang.Object	_remove(java.lang.Object key)
void	addNotifier(DistributedHashtable.Notification n)
void	block() Block sending and receiving of messages until ViewAccepted is called
void	clear() Clears this hashtable so that it contains no keys
Channel	getChannel()
java.lang.String	getGroupName()
Address	getLocalAddress()
boolean	getPersistent()
byte[]	getState() Answers the group state; e.g., when joining.
protected void	init(long state_timeout)
static void	main(java.lang.String[] args)
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Maps the specified key to the specified value in the hashtable.
void	putAll(java.util.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.
void	receive(Message msg) Called when a message is received.
java.lang.Object	remove(java.lang.Object key) Removes the key (and its corresponding value) from the Hashtable.
void	removeNotifier(DistributedHashtable.Notification n)
void	setDeadlockDetection(boolean flag)
void	setPersistent(boolean p)
void	setState(byte[] new_state) Sets the group state; e.g., when joining.
void	start(long state_timeout) Fetches the state
void	stop()
void	suspect(Address suspected_mbr) Called when a member is suspected
void	viewAccepted(View new_view) Called when a change in membership has occurred.

Methods inherited from class java.util.Hashtable

clone, contains, containsKey, containsValue, elements, entrySet, equals, get, hashCode, isEmpty, keys, keySet, rehash, size, toString, values

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

disp

protected transient RpcDispatcher disp

state_promise

protected final transient Promise state_promise

log

protected final org.apache.commons.logging.Log log

Constructor Detail

DistributedHashtable

public DistributedHashtable(java.lang.String groupname,
                    ChannelFactory factory,
                    java.lang.String properties,
                    long state_timeout)
                     throws ChannelException

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. This will override the properties of the factory. If null, then the factory properties will be used

state_timeout - The time to wait until state is retrieved in milliseconds. A value of 0 means wait forever.

Throws:

ChannelException

DistributedHashtable

public DistributedHashtable(java.lang.String groupname,
                    ChannelFactory factory,
                    java.lang.String properties,
                    boolean persistent,
                    long state_timeout)
                     throws ChannelException

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. This will override the properties of the factory. If null, then the factory properties will be used

persistent - Whether the contents should be persisted

state_timeout - Max number of milliseconds to wait until state is retrieved

Throws:

ChannelException

DistributedHashtable

public DistributedHashtable(Channel channel,
                    long state_timeout)

DistributedHashtable

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

DistributedHashtable

public DistributedHashtable(PullPushAdapter adapter,
                    java.io.Serializable id,
                    long state_timeout)
                     throws ChannelNotConnectedException,
                            ChannelClosedException

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

Throws:

ChannelNotConnectedException

ChannelClosedException

DistributedHashtable

public DistributedHashtable(PullPushAdapter adapter,
                    java.io.Serializable id)

Method Detail

init

protected final void init(long state_timeout)

start

public final void start(long state_timeout)
                 throws ChannelClosedException,
                        ChannelNotConnectedException

Fetches the state

Parameters:

state_timeout -

Throws:

ChannelClosedException

ChannelNotConnectedException

getLocalAddress

public Address getLocalAddress()

getGroupName

public java.lang.String getGroupName()

getChannel

public Channel getChannel()

getPersistent

public boolean getPersistent()

setPersistent

public void setPersistent(boolean p)

setDeadlockDetection

public void setDeadlockDetection(boolean flag)

addNotifier

public void addNotifier(DistributedHashtable.Notification n)

removeNotifier

public void removeNotifier(DistributedHashtable.Notification n)

stop

public void stop()

put

public java.lang.Object put(java.lang.Object key,
                   java.lang.Object value)

Maps the specified key to the specified value in the hashtable. Neither of both parameters can be null

Specified by:

put in interface java.util.Map

Overrides:

put in class java.util.Hashtable

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(java.util.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.

Specified by:

putAll in interface java.util.Map

Overrides:

putAll in class java.util.Hashtable

Parameters:

m - - Mappings to be stored in this map

clear

public void clear()

Clears this hashtable so that it contains no keys

Specified by:

clear in interface java.util.Map

Overrides:

clear in class java.util.Hashtable

remove

public java.lang.Object remove(java.lang.Object key)

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

Specified by:

remove in interface java.util.Map

Overrides:

remove in class java.util.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.

_put

public java.lang.Object _put(java.lang.Object key,
                    java.lang.Object value)

_putAll

public void _putAll(java.util.Map m)

See Also:

Map.putAll(java.util.Map)

_clear

public void _clear()

_remove

public java.lang.Object _remove(java.lang.Object key)

receive

public void receive(Message msg)

Description copied from interface: MessageListener

Called when a message is received.

Specified by:

receive in interface MessageListener

getState

public byte[] getState()

Description copied from interface: MessageListener

Answers the group state; e.g., when joining.

Specified by:

getState in interface MessageListener

Returns:

byte[]

setState

public void setState(byte[] new_state)

Description copied from interface: MessageListener

Sets the group state; e.g., when joining.

Specified by:

setState in interface MessageListener

viewAccepted

public void viewAccepted(View new_view)

Description copied from interface: MembershipListener

Called when a change in membership has occurred. No long running actions should be done in this callback. If some long running action needs to be performed, it should be done in a separate thread.

Specified by:

viewAccepted in interface MembershipListener

suspect

public void suspect(Address suspected_mbr)

Called when a member is suspected

Specified by:

suspect in interface MembershipListener

block

public void block()

Block sending and receiving of messages until ViewAccepted is called

Specified by:

block in interface MembershipListener

main

public static void main(java.lang.String[] args)