org.jgroups.blocks

Class GroupRequest<T>

java.lang.Object

org.jgroups.blocks.Request

org.jgroups.blocks.GroupRequest<T>

All Implemented Interfaces:

Future, RspCollector, NotifyingFuture

public class GroupRequest<T>
extends Request

Sends a message to all members of the group and waits for all responses (or timeout). Returns a boolean value (success or failure). Results (if any) can be retrieved when done.

The supported transport to send requests is currently either a RequestCorrelator or a generic Transport. One of them has to be given in the constructor. It will then be used to send a request. When a message is received by either one, the receiveResponse() of this class has to be called (this class does not actively receive requests/responses itself). Also, when a view change or suspicion is received, the methods viewChange() or suspect() of this class have to be called.

When started, an array of responses, correlating to the membership, is created. Each response is added to the corresponding field in the array. When all fields have been set, the algorithm terminates. This algorithm can optionally use a suspicion service (failure detector) to detect (and exclude from the membership) fauly members. If no suspicion service is available, timeouts can be used instead (see execute()). When done, a list of suspected members can be retrieved.

Because a channel might deliver requests, and responses to different requests, the GroupRequest class cannot itself receive and process requests/responses from the channel. A mechanism outside this class has to do this; it has to determine what the responses are for the message sent by the execute() method and call receiveResponse() to do so.

Requirements: lossless delivery, e.g. acknowledgment-based message confirmation.

Author:

Bela Ban

Field Summary

Fields inherited from class org.jgroups.blocks.Request

block_for_results, completed, corr, done, listener, lock, log, options, req_id, REQUEST_ID, request_msg

Constructor Summary

Constructors

Constructor and Description
GroupRequest(Message msg, RequestCorrelator corr, Address target, RequestOptions options)
GroupRequest(Message msg, RequestCorrelator corr, Collection<Address> targets, RequestOptions options)

Method Summary

Methods

Modifier and Type	Method and Description
RspList<T>	get()
RspList<T>	get(long timeout, TimeUnit unit)
boolean	getAnycasting()
RspList<T>	getResults() Returns the results as a RspList
void	receiveResponse(Object response_value, Address sender, boolean is_exception) Callback (called by RequestCorrelator or Transport).
protected boolean	responsesComplete()
void	sendRequest()
void	setAnycasting(boolean anycasting)
void	suspect(Address suspected_member) Callback (called by RequestCorrelator or Transport).
String	toString()
void	viewChange(View new_view) Any member of 'membership' that is not in the new view is flagged as SUSPECTED.

Methods inherited from class org.jgroups.blocks.Request

cancel, checkCompletion, execute, getBlockForResults, getRequestId, getResponsesComplete, isCancelled, isDone, responsesComplete, setBlockForResults, setListener, setResponseFilter, waitForResults

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

GroupRequest

public GroupRequest(Message msg,
            RequestCorrelator corr,
            Collection<Address> targets,
            RequestOptions options)

Parameters:

msg - The message to be sent

corr - The request correlator to be used. A request correlator sends requests tagged with a unique ID and notifies the sender when matching responses are received. The reason GroupRequest uses it instead of a Transport is that multiple requests/responses might be sent/received concurrently

targets - The targets, which are supposed to receive the message. Any receiver not in this set will discard the message. Targets are always a subset of the current membership

options - The request options to be used for this call

GroupRequest

public GroupRequest(Message msg,
            RequestCorrelator corr,
            Address target,
            RequestOptions options)

Method Detail

getAnycasting

public boolean getAnycasting()

setAnycasting

public void setAnycasting(boolean anycasting)

sendRequest

public void sendRequest()
                 throws Exception

Specified by:

sendRequest in class Request

Throws:

Exception

receiveResponse

public void receiveResponse(Object response_value,
                   Address sender,
                   boolean is_exception)

Callback (called by RequestCorrelator or Transport). Adds a response to the response table. When all responses have been received, execute() returns.

Specified by:

receiveResponse in interface RspCollector

Specified by:

receiveResponse in class Request

suspect

public void suspect(Address suspected_member)

Callback (called by RequestCorrelator or Transport). Report to GroupRequest that a member is reported as faulty (suspected). This method would probably be called when getting a suspect message from a failure detector (where available). It is used to exclude faulty members from the response list.

Specified by:

suspect in interface RspCollector

Specified by:

suspect in class Request

viewChange

public void viewChange(View new_view)

Any member of 'membership' that is not in the new view is flagged as SUSPECTED. Any member in the new view that is not in the membership (ie, the set of responses expected for the current RPC) will not be added to it. If we did this we might run into the following problem:

• Membership is {A,B}
• A sends a synchronous group RPC (which sleeps for 60 secs in the invocation handler)
• C joins while A waits for responses from A and B
• If this would generate a new view {A,B,C} and if this expanded the response set to {A,B,C}, A would wait forever on C's response because C never received the request in the first place, therefore won't send a response.

Specified by:

viewChange in interface RspCollector

Specified by:

viewChange in class Request

getResults

public RspList<T> getResults()

Returns the results as a RspList

get

public RspList<T> get()
               throws InterruptedException,
                      ExecutionException

Throws:

InterruptedException

ExecutionException

get

public RspList<T> get(long timeout,
             TimeUnit unit)
               throws InterruptedException,
                      ExecutionException,
                      TimeoutException

Throws:

InterruptedException

ExecutionException

TimeoutException

toString

public String toString()

Overrides:

toString in class Request

responsesComplete

protected boolean responsesComplete()

Specified by:

responsesComplete in class Request