org.jgroups.stack

Class MessageProtocol

Implemented Interfaces:
RequestHandler
Known Direct Subclasses:
FLOW_CONTROL, 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.

Author:
Bela Ban

Field Summary

protected RequestCorrelator
_corr
protected Vector
members

Fields inherited from class org.jgroups.stack.Protocol

down_handler, down_prot, down_queue, down_thread, down_thread_prio, log, observer, props, stack, up_handler, up_prot, up_queue, up_thread, up_thread_prio

Method Summary

RspList
castMessage(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.
Object
handle(Message req)
Processes a request destined for this layer.
protected boolean
handleDownEvent(Event evt)
Handle down event.
protected boolean
handleUpEvent(Event evt)
Handle up event.
Object
sendMessage(Message msg, int mode, long timeout)
Sends a message to a single member (destination = msg.dest) and returns the response.
void
start()
void
stop()
void
up(Event evt)
Handle an event coming from the layer above
protected void
updateView(View new_view)

Methods inherited from class org.jgroups.stack.Protocol

destroy, down, getDownProtocol, getDownQueue, getName, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setProperties, setPropertiesInternal, setProtocolStack, setUpProtocol, start, startDownHandler, startUpHandler, stop, stopInternal, up

Field Details

_corr

protected RequestCorrelator _corr

members

protected Vector members

Method Details

castMessage

public RspList castMessage(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.

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 interface Protocol

handle

public Object handle(Message req)
Processes a request destined for this layer. The return value is sent as response.
Specified by:
handle in interface RequestHandler

handleDownEvent

protected boolean handleDownEvent(Event evt)
Handle down event. Return false if it should not be passed down the stack.

handleUpEvent

protected boolean handleUpEvent(Event evt)
Handle up event. Return false if it should not be passed up the stack.

sendMessage

public Object sendMessage(Message msg,
                          int mode,
                          long timeout)
            throws TimeoutException,
                   SuspectedException
Sends a message to a single member (destination = msg.dest) and returns the response. The message's destination must be non-zero !

start

public void start()
            throws Exception
Overrides:
start in interface Protocol

stop

public void stop()
Overrides:
stop in interface Protocol

up

public final void up(Event evt)
Handle an event coming from the layer above
Overrides:
up in interface Protocol

updateView

protected void updateView(View new_view)

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