JavaGroups
Class GroupRequest

java.lang.Object
  |
  +--JavaGroups.GroupRequest

public class GroupRequest

extends java.lang.Object

implements RspCollector

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.

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. acknowledgement-based message confirmation.

Field Summary

static int	GET_ABS_MAJORITY
static int	GET_ALL
static int	GET_FIRST
static int	GET_MAJORITY
static int	GET_N
static int	GET_NONE

Constructor Summary

GroupRequest(Message m, RequestCorrelator corr, java.util.Vector members, int rsp_mode)

GroupRequest(Message m, RequestCorrelator corr, java.util.Vector members, int rsp_mode, long timeout, int expected_mbrs)

Method Summary

boolean	Execute() Sends the message.
int	GetNumSuspects()
RspList	GetResults() Returns the results as a RspList.
java.util.Vector	GetSuspects()
boolean	IsDone()
void	ReceiveResponse(Message m) Callback (called by RequestCorrelator).
void	Reset(Message m, int mode, long timeout) Resets the group request, so it can be reused for another execution.
void	Reset(Message m, java.util.Vector members, int rsp_mode, long timeout, int expected_rsps)
void	Reset(java.util.Vector members)
void	Suspect(java.lang.Object suspected_member) Callback (called by RequestCorrelator).
java.lang.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 java.lang.Object

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

Field Detail

GET_FIRST

public static final int GET_FIRST

GET_ALL

public static final int GET_ALL

GET_MAJORITY

public static final int GET_MAJORITY

GET_ABS_MAJORITY

public static final int GET_ABS_MAJORITY

GET_N

public static final int GET_N

GET_NONE

public static final int GET_NONE

Constructor Detail

GroupRequest

public GroupRequest(Message m,
                    RequestCorrelator corr,
                    java.util.Vector members,
                    int rsp_mode)

Parameters:

m - 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.

members - The initial membership. This value reflects the membership to which the request is sent (and from which potential responses are expected). Is reset by Reset().

rsp_mode - How many responses are expected. Can be

1. GET_ALL: wait for all responses from non-suspected members. A suspicion service might warn us when a member from which a response is outstanding has crashed, so it can be excluded from the responses. If no suspision service is available, a timeout can be used (a value of 0 means wait forever). If a timeout of 0 is used, no suspicion service is available and a member from which we expect a response has crashed, this methods blocks forever !.
2. GET_FIRST: wait for the first available response.
3. GET_MAJORITY: wait for the majority of all responses. The majority is re-computed when a member is suspected.
4. GET_ABS_MAJORITY: wait for the majority of all members. This includes failed members, so it may block if no timeout is specified.
5. GET_N: wait for N members. Return if n is >= membership+suspects.
6. GET_NONE: don't wait for any response. Essentially send an asynchronous message to the group members.

expected_mbrs - Number of responses expected (used with GET_ALL).

GroupRequest

public GroupRequest(Message m,
                    RequestCorrelator corr,
                    java.util.Vector members,
                    int rsp_mode,
                    long timeout,
                    int expected_mbrs)

Parameters:

timeout - Time to wait for responses (ms). A value of <= 0 means wait indefinitely (e.g. if a suspicion service is available; timeouts are not needed).

Method Detail

Execute

public boolean Execute()

Sends the message. Returns when n responses have been received, or when a timeout has occurred. n can be the first response, all responses, or a majority of the responses.

Reset

public void Reset(Message m,
                  int mode,
                  long timeout)

Resets the group request, so it can be reused for another execution.

Reset

public void Reset(Message m,
                  java.util.Vector members,
                  int rsp_mode,
                  long timeout,
                  int expected_rsps)

Reset

public void Reset(java.util.Vector members)

ReceiveResponse

public void ReceiveResponse(Message m)

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

Specified by:

ReceiveResponse in interface RspCollector

Suspect

public void Suspect(java.lang.Object suspected_member)

Callback (called by RequestCorrelator). 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

ViewChange

public void ViewChange(View new_view)

Any member of 'membership' that is not in the new view is flagged as SUSPECTED.

Specified by:

ViewChange in interface RspCollector

GetResults

public RspList GetResults()

Returns the results as a RspList.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

GetNumSuspects

public int GetNumSuspects()

GetSuspects

public java.util.Vector GetSuspects()

IsDone

public boolean IsDone()