JavaGroups.JavaStack
Class MessageProtocol

java.lang.Object
  |
  +--JavaGroups.JavaStack.Protocol
        |
        +--JavaGroups.JavaStack.MessageProtocol

Direct Known Subclasses:

MessageProtocolEXAMPLE, RpcProtocol

public abstract class MessageProtocol

extends Protocol

implements RequestHandler

Based on Protocol, but incorporates RequestCorrelator and GroupRequest: the latter can be used to mcast messages to all members and receive their reponses.

A protocol based on this template can send messages to all members and receive all, a single, n, or none responses. Requests directed towards the protocol can be handled by overriding method Handle.

Requests and responses are in the form of Messages, which would typically need to contain information pertaining to the request/response, e.g. in the form of objects contained in the message. To use remote method calls, use RpcProtocol instead.

Typical use of of a MessageProtocol would be when a protocol needs to interact with its peer protocols at each of the members' protocol stacks. A simple protocol like fragmentation, which does not need to interact with other instances of fragmentation, may simply subclass Protocol instead.

Constructor Summary

MessageProtocol()

Method Summary

RspList	CastMessage(java.util.Vector dests, Message msg, int mode, long timeout) Cast a message to all members, and wait for mode responses.
void	Down(Event evt) This message is not originated by this layer, therefore we can just pass it down without having to go through the request correlator.
java.lang.Object	Handle(Message req) Processes a request destined for this layer.
java.lang.Object	SendMessage(Message msg, int mode, long timeout) Sends a message to a single member (destination = msg.dest) and returns the response.
void	Up(Event evt) An event was received from the layer below.

Methods inherited from class JavaGroups.JavaStack.Protocol

GetDownProtocol, GetName, GetProperties, GetUpProtocol, PassDown, PassUp, ProvidedDownServices, ProvidedUpServices, RequiredDownServices, RequiredUpServices, Reset, SetDownProtocol, SetProperties, SetProtocolStack, SetUpProtocol, StartDownHandler, StartUpHandler, StopInternal

Methods inherited from class java.lang.Object

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

Constructor Detail

MessageProtocol

public MessageProtocol()

Method Detail

CastMessage

public RspList CastMessage(java.util.Vector dests,
                           Message msg,
                           int mode,
                           long timeout)

Cast a message to all members, and wait for mode responses. The responses are returned in a response list, where each response is associated with its sender.

Uses GroupRequest.

Parameters:

dests - The members from which responses are expected. If it is null, replies from all members are expected. The request itself is multicast to all members.

msg - The message to be sent to n members

mode - Defined in GroupRequest. The number of responses to wait for:

1. GET_FIRST: return the first response received.
2. GET_ALL: wait for all responses (minus the ones from suspected members)
3. GET_MAJORITY: wait for a majority of all responses (relative to the grp size)
4. GET_ABS_MAJORITY: wait for majority (absolute, computed once)
5. GET_N: wait for n responses (may block if n > group size)
6. GET_NONE: wait for no responses, return immediately (non-blocking)

timeout - If 0: wait forever. Otherwise, wait for mode responses or timeout time.

Returns:

RspList A list of responses. Each response is an Object and associated to its sender.

SendMessage

public java.lang.Object SendMessage(Message msg,
                                    int mode,
                                    long timeout)
                             throws Timeout,
                                    Suspected

Sends a message to a single member (destination = msg.dest) and returns the response. The message's destination must be non-zero !

Handle

public java.lang.Object Handle(Message req)

Processes a request destined for this layer. The return value is sent as response.

Specified by:

Handle in interface RequestHandler

Up

public final void Up(Event evt)

Description copied from class: Protocol

An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using PassDown or c) the event (or another event) is sent up the stack using PassUp.

Overrides:

Up in class Protocol

Down

public final void Down(Event evt)

This message is not originated by this layer, therefore we can just pass it down without having to go through the request correlator. We do this ONLY for messages !

Overrides:

Down in class Protocol