org.javagroups.blocks
Class GroupRequest

java.lang.Object
  |
  +--org.javagroups.blocks.GroupRequest
All Implemented Interfaces:
Command, RspCollector

public class GroupRequest
extends java.lang.Object
implements RspCollector, Command

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.

Version:
$Revision: 1.27 $
Author:
Bela Ban

Field Summary
protected  RequestCorrelator corr
           
protected  boolean done
           
protected  int expected_mbrs
           
static int GET_ABS_MAJORITY
          return majority (of all members, may block)
static int GET_ALL
          return all responses
static int GET_FIRST
          return only first response
static int GET_MAJORITY
          return majority (of all non-faulty members)
static int GET_N
          return n responses (may block)
static int GET_NONE
          return no response (async call)
protected  long req_id
           
protected  Message request_msg
           
protected  int rsp_mode
           
protected  java.lang.Object rsp_mutex
           
protected  long timeout
           
protected  Transport transport
           
 
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)
           
GroupRequest(Message m, Transport transport, java.util.Vector members, int rsp_mode)
           
GroupRequest(Message m, Transport transport, java.util.Vector members, int rsp_mode, long timeout, int expected_mbrs)
           
 
Method Summary
protected  int determineMajority(int i)
           
protected  boolean doExecute(long timeout)
          This method runs with rsp_mutex locked (called by execute()).
 boolean execute()
          Sends the message.
 int getNumSuspects()
           
protected  boolean getResponses()
           
 RspList getResults()
          Returns the results as a RspList
 java.util.Vector getSuspects()
           
 boolean isDone()
           
 void receiveResponse(Message m)
          Callback (called by RequestCorrelator or Transport).
 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 mbrs)
          This method sets the membership variable to the value of members.
 void suspect(Address suspected_member)
          Callback (called by RequestCorrelator or Transport).
 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
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

GET_FIRST

public static final int GET_FIRST
return only first response

See Also:
Constant Field Values

GET_ALL

public static final int GET_ALL
return all responses

See Also:
Constant Field Values

GET_MAJORITY

public static final int GET_MAJORITY
return majority (of all non-faulty members)

See Also:
Constant Field Values

GET_ABS_MAJORITY

public static final int GET_ABS_MAJORITY
return majority (of all members, may block)

See Also:
Constant Field Values

GET_N

public static final int GET_N
return n responses (may block)

See Also:
Constant Field Values

GET_NONE

public static final int GET_NONE
return no response (async call)

See Also:
Constant Field Values

request_msg

protected Message request_msg

corr

protected RequestCorrelator corr

transport

protected Transport transport

rsp_mode

protected int rsp_mode

done

protected boolean done

rsp_mutex

protected java.lang.Object rsp_mutex

timeout

protected long timeout

expected_mbrs

protected int expected_mbrs

req_id

protected long req_id
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.

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).

GroupRequest

public GroupRequest(Message m,
                    Transport transport,
                    java.util.Vector members,
                    int rsp_mode)

GroupRequest

public GroupRequest(Message m,
                    Transport transport,
                    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 a timeout has occurred. n can be the first response, all responses, or a majority of the responses.

Specified by:
execute in interface Command

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 mbrs)
This method sets the membership variable to the value of members. It requires that the caller already hold the rsp_mutex lock.

Parameters:
mbrs - The new list of members

receiveResponse

public void receiveResponse(Message m)
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

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

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:

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()

determineMajority

protected int determineMajority(int i)

doExecute

protected boolean doExecute(long timeout)
This method runs with rsp_mutex locked (called by execute()).


getResponses

protected boolean getResponses()


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