Package org.jgroups.blocks

Class GroupRequest

java.lang.Object
org.jgroups.blocks.Request
org.jgroups.blocks.GroupRequest
All Implemented Interfaces:
Future, RspCollector, Command, NotifyingFuture
public class GroupRequest 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

  • Constructor Details

    • 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 m, RequestCorrelator corr, Address target, RequestOptions options)

    • GroupRequest

      public GroupRequest(Message m, Transport transport, Collection<Address> mbrs, RequestOptions options)

  • Method Details

    • 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)
      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 getResults()
      Returns the results as a RspList

    • get

      public RspList get() throws InterruptedException, ExecutionException
      Throws:
      InterruptedException
      ExecutionException

    • get

      public RspList 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