de.zib.scalaris
Class DefaultConnectionPolicy

java.lang.Object
  de.zib.scalaris.ConnectionPolicy
      de.zib.scalaris.DefaultConnectionPolicy

Direct Known Subclasses:

RoundRobinConnectionPolicy

public class DefaultConnectionPolicy
extends ConnectionPolicy

Implements a ConnectionPolicy by choosing nodes randomly. Sorts nodes into two lists:

• good nodes
• bad nodes

Nodes that failed during a connection or in an attempt to connect will be transferred to the bad nodes list badNodes. When a connection attempt to a node is successful, it will be removed from this list and put into the good nodes list goodNodes and the node's connection failure statistics will be reset using PeerNode.resetFailureCount(). Whenever a node is being selected for a new connection (or reconnect), it will select one randomly from the goodNodes list. If this list is empty, it will select the least recently failed node from badNodes. At most maxRetries retries are attempted per operation (see Connection.connect(), Connection.doRPC(String, String, com.ericsson.otp.erlang.OtpErlangList) and Connection.doRPC(String, String, com.ericsson.otp.erlang.OtpErlangObject[]) ) - the number of the current attempt will not be cached in this class. Set the maximal number of retries using setMaxRetries(int). Attention: All member's functions are synchronised as there can be a single connection policy object used by many threads and the access to the goodNodes and badNodes members are logically linked together and operations on both need to be performed atomically. Additionally access to PeerNode objects are synchronised on themselves. It is therefore important not to use any of this classes methods in blocks that synchronise on any node object. Otherwise deadlocks might occur!!

Since:

2.3

Version:

2.3

Author:

Nico Kruber, kruber@zib.de

Constructor Summary

DefaultConnectionPolicy(List<PeerNode> availableRemoteNodes)
Creates a new connection policy with the given remote nodes.

DefaultConnectionPolicy(PeerNode remoteNode)
Creates a new connection policy working with the given remote node.

Method Summary

void	availableNodeAdded(PeerNode newNode) Adds the given node to the goodNodes list if it has no failures, otherwise it will be added to badNodes.
void	availableNodeRemoved(PeerNode removedNode) Removes the node from the goodNodes and badNodes lists.
void	availableNodesReset() Resets the goodNodes and badNodes members as the list of available nodes has been reset.
List<PeerNode>	getBadNodes() Gets a copy of the list of good nodes (contains references to the PeerNode objects).
List<PeerNode>	getGoodNodes() Gets a copy of the list of good nodes (contains references to the PeerNode objects).
int	getMaxRetries() Sets the maximal number of automatic connection retries.
void	nodeConnectSuccess(PeerNode node) Sets the node's last successful connect time stamp, resets its failure statistics and moves it to the goodNodes list.
void	nodeFailed(PeerNode node) Sets the given node's last failed connect time stamp and moves it to the badNodes list.
void	nodeFailReset(PeerNode node) Acts upon a failure reset of the given node.
<E extends Exception> PeerNode	selectNode(int retry, PeerNode failedNode, E e) Selects the node to (re-)connect with until the maximal number of maxRetries has been reached.
void	setMaxRetries(int maxRetries) Gets the maximal number of automatic connection retries.

Methods inherited from class de.zib.scalaris.ConnectionPolicy

selectNode

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DefaultConnectionPolicy

public DefaultConnectionPolicy(PeerNode remoteNode)

Creates a new connection policy working with the given remote node. Provided for convenience. Attention: This method also synchronises on the node.

Parameters:

remoteNode - the (only) available remote node

DefaultConnectionPolicy

public DefaultConnectionPolicy(List<PeerNode> availableRemoteNodes)

Creates a new connection policy with the given remote nodes. Attention: This method synchronises on availableRemoteNodes. Any time this list is changed, the according methods in this class should be called, i.e. availableNodeAdded(PeerNode), availableNodeRemoved(PeerNode), availableNodesReset() to update the good and bad nodes lists.

Parameters:

availableRemoteNodes - the remote nodes available for connections

Method Detail

availableNodeAdded

public void availableNodeAdded(PeerNode newNode)

Adds the given node to the goodNodes list if it has no failures, otherwise it will be added to badNodes. Attention: This method also synchronises on the node.

Overrides:

availableNodeAdded in class ConnectionPolicy

Parameters:

newNode - the new node

availableNodeRemoved

public void availableNodeRemoved(PeerNode removedNode)

Removes the node from the goodNodes and badNodes lists.

Overrides:

availableNodeRemoved in class ConnectionPolicy

Parameters:

removedNode - the removed node

availableNodesReset

public void availableNodesReset()

Resets the goodNodes and badNodes members as the list of available nodes has been reset.

Overrides:

availableNodesReset in class ConnectionPolicy

nodeFailed

public void nodeFailed(PeerNode node)

Sets the given node's last failed connect time stamp and moves it to the badNodes list. Attention: This method also synchronises on the node.

Overrides:

nodeFailed in class ConnectionPolicy

Parameters:

node - the failed node

nodeFailReset

public void nodeFailReset(PeerNode node)

Acts upon a failure reset of the given node. Resets the node's last failure state.

Overrides:

nodeFailReset in class ConnectionPolicy

Parameters:

node - the node

nodeConnectSuccess

public void nodeConnectSuccess(PeerNode node)

Sets the node's last successful connect time stamp, resets its failure statistics and moves it to the goodNodes list. Attention: This method also synchronises on the node.

Overrides:

nodeConnectSuccess in class ConnectionPolicy

Parameters:

node - the node

selectNode

public <E extends Exception> PeerNode selectNode(int retry,
                                                 PeerNode failedNode,
                                                 E e)
                    throws E extends Exception

Selects the node to (re-)connect with until the maximal number of maxRetries has been reached. Throws an exception if retry > maxRetries and thus stops further node connection attempts. Otherwise chooses a random good node or (if there are no good nodes) the least recently failed bad node.

Specified by:

selectNode in class ConnectionPolicy

Type Parameters:

E - the type of the exception that came from the failed connection and may be re-thrown

Parameters:

retry - the n'th retry (initial connect = 0, 1st reconnect = 1,...)

failedNode - the node from the previous connection attempt or null

e - the exception that came back from the previous connection attempt or null

Returns:

the new node to connect with

Throws:

E - if thrown, automatic re-connection attempts will stop

UnsupportedOperationException - is thrown if the operation can not be performed, e.g. the list is empty

E extends Exception

See Also:

Connection.connect(), Connection.doRPC(String, String, com.ericsson.otp.erlang.OtpErlangList), Connection.doRPC(String, String, com.ericsson.otp.erlang.OtpErlangObject[])

getMaxRetries

public int getMaxRetries()

Sets the maximal number of automatic connection retries.

Returns:

the maxRetries

setMaxRetries

public void setMaxRetries(int maxRetries)

Gets the maximal number of automatic connection retries.

Parameters:

maxRetries - the maxRetries to set (>= 0)

getGoodNodes

public List<PeerNode> getGoodNodes()

Gets a copy of the list of good nodes (contains references to the PeerNode objects).

Returns:

the list of good nodes

getBadNodes

public List<PeerNode> getBadNodes()

Gets a copy of the list of good nodes (contains references to the PeerNode objects).

Returns:

the list of good nodes