rice.p2p.scribe
Interface ScribePolicy

All Known Implementing Classes:

ScribePolicy.DefaultScribePolicy, ScribePolicy.LimitedScribePolicy, ScribeRegrTest.TestScribePolicy, SplitStreamScribePolicy

public interface ScribePolicy

Version:

$Id: ScribePolicy.java 4098 2008-02-13 09:36:33Z jeffh $

Author:

Alan Mislove

Nested Class Summary

static class	ScribePolicy.DefaultScribePolicy The default policy for Scribe, which always allows new children to join and adds children in the order in which they are provided, implicitly providing a depth-first search.
static class	ScribePolicy.LimitedScribePolicy An optional policy for Scribe, which allows up to a specified number of children per topic.

Method Summary

java.util.List<Topic>	allowSubscribe(Scribe scribe, NodeHandle source, java.util.List<Topic> topics, ScribeContent content) This method is called when the newChild is about to become our child, and the policy should return whether or not the child should be allowed to become our child.
void	childAdded(Topic topic, NodeHandle child) Informs this policy that a child was added to a topic - the topic is free to ignore this upcall if it doesn't care.
void	childRemoved(Topic topic, NodeHandle child) Informs this policy that a child was removed from a topic - the topic is free to ignore this upcall if it doesn't care.
void	directAnycast(AnycastMessage message, NodeHandle parent, java.util.Collection<NodeHandle> children) This method is called when an anycast is received which is not satisfied at the local node.
ScribeContent	divideContent(java.util.List<Topic> theTopics, ScribeContent content) This method is called when the ScribeImpl splits a SubscribeMessage into multiple parts.
void	intermediateNode(ScribeMessage message) This is invoked whenever this message arrives on any overlay node, this gives the ScribeClient's power to tap into some datastructures they might wanna edit
void	recvAnycastFail(Topic topic, NodeHandle failedAtNode, ScribeContent content) This notifies us when we receive a failure for a anycast

Method Detail

allowSubscribe

java.util.List<Topic> allowSubscribe(Scribe scribe,
                                     NodeHandle source,
                                     java.util.List<Topic> topics,
                                     ScribeContent content)

This method is called when the newChild is about to become our child, and the policy should return whether or not the child should be allowed to become our child. If the length of children and clients is both 0, allowing the child to join will have the effect of implicitly subscribing this node the the given topic. For each Topic that you are willing to accept, call message.accept(Topic); Here is some example code:

 Iterator i = topics.iterator();
 while (i.hasNext()) {
   Topic topic = i.next();
   if (!accept(topic)) { // your decision on what to do for the topic
     i.remove();
   }
 }
 return topics;
 

Or, to accept all:

 return topics;
 

Some calls that are likely useful are:

• scribe.getChildren(topic)
• scribe.getClients(topic)

If only some of the topics are accepted, the content may need to be modified. This method is allowed to modify the content.

Parameters:

scribe - the Scribe that is making the request

source - the subscriber

topics - the topics that are requested

content - the content that came with the message

return - the list that is accepted

directAnycast

void directAnycast(AnycastMessage message,
                   NodeHandle parent,
                   java.util.Collection<NodeHandle> children)

This method is called when an anycast is received which is not satisfied at the local node. This method should add both the parent and child nodes to the anycast's to-search list, but this method allows different policies concerning the order of the adding as well as selectively adding nodes.

Parameters:

message - The anycast message in question

parent - Our current parent for this message's topic

children - Our current children for this message's topic

childAdded

void childAdded(Topic topic,
                NodeHandle child)

Informs this policy that a child was added to a topic - the topic is free to ignore this upcall if it doesn't care.

Parameters:

topic - The topic to unsubscribe from

child - The child that was added

childRemoved

void childRemoved(Topic topic,
                  NodeHandle child)

Informs this policy that a child was removed from a topic - the topic is free to ignore this upcall if it doesn't care.

Parameters:

topic - The topic to unsubscribe from

child - The child that was removed

recvAnycastFail

void recvAnycastFail(Topic topic,
                     NodeHandle failedAtNode,
                     ScribeContent content)

This notifies us when we receive a failure for a anycast

intermediateNode

void intermediateNode(ScribeMessage message)

This is invoked whenever this message arrives on any overlay node, this gives the ScribeClient's power to tap into some datastructures they might wanna edit

divideContent

ScribeContent divideContent(java.util.List<Topic> theTopics,
                            ScribeContent content)

This method is called when the ScribeImpl splits a SubscribeMessage into multiple parts. If you modify the content, you must make a copy, as the same content will be passed in for the other divisions of the SubscribeMessage. ScribeContent's are not naturally copyable, so Scribe cannot make a copy apriori.

Parameters:

theTopics - topics going to a particular location

content - the content that may need to be divided

Returns:

the content if not changed, a new ScribeContent if changed