Package org.jgroups.protocols.pbcast

Class FLUSH

  • public class FLUSH
extends Protocol
    Flush, as it name implies, forces group members to flush their pending messages while blocking them to send any additional messages. The process of flushing acquiesces the group so that state transfer or a join can be done. It is also called stop-the-world model as nobody will be able to send messages while a flush is in process.

    Flush is needed for:

    (1) State transfer. When a member requests state transfer, the coordinator tells everyone to stop sending messages and waits for everyone's ack. Then it asks the application for its state and ships it back to the requester. After the requester has received and set the state successfully, the coordinator tells everyone to resume sending messages.

    (2) View changes (e.g.a join). Before installing a new view V2, flushing would ensure that all messages *sent* in the current view V1 are indeed *delivered* in V1, rather than in V2 (in all non-faulty members). This is essentially Virtual Synchrony.

    Since:
    2.4
    Author:
    Vladimir Blagojevic

    • Field Detail

      • timeout

        protected long timeout

      • start_flush_timeout

        protected long start_flush_timeout

      • end_flush_timeout

        protected long end_flush_timeout

      • retry_timeout

        protected long retry_timeout

      • enable_reconciliation

        protected boolean enable_reconciliation

      • bypass

        protected boolean bypass

    • Constructor Detail

      • FLUSH

        public FLUSH()

    • Method Detail

      • getStartFlushTimeout

        public long getStartFlushTimeout()

      • setStartFlushTimeout

        public void setStartFlushTimeout​(long start_flush_timeout)

      • getRetryTimeout

        public long getRetryTimeout()

      • setRetryTimeout

        public void setRetryTimeout​(long retry_timeout)

      • start

        public void start()
           throws java.lang.Exception
        Description copied from class: Protocol
        This method is called on a JChannel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.
        Overrides:
        start in class Protocol
        Throws:
        java.lang.Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so JChannel.connect(String) will throw an exception

      • stop

        public void stop()
        Description copied from class: Protocol
        This method is called on a JChannel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed
        Overrides:
        stop in class Protocol

      • getAverageFlushDuration

        public double getAverageFlushDuration()

      • getTotalTimeInFlush

        public long getTotalTimeInFlush()

      • getNumberOfFlushes

        public int getNumberOfFlushes()

      • setBypass

        public boolean setBypass​(boolean flag)

      • startFlush

        public void startFlush()

      • stopFlush

        public void stopFlush()

      • down

        public java.lang.Object down​(Event evt)
        Description copied from class: Protocol
        An event is to be sent down the stack. A protocol may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the protocol may need to add a header to it (or do nothing at all) before sending it down the stack using down_prot.down().
        Overrides:
        down in class Protocol

      • down

        public java.lang.Object down​(Message msg)
        Description copied from class: Protocol
        A message is sent down the stack. Protocols may examine the message and do something (e.g. add a header) with it before passing it down.
        Overrides:
        down in class Protocol

      • up

        public java.lang.Object up​(Event evt)
        Description copied from class: Protocol
        An event was received from the protocol below. Usually the current protocol will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using down_prot.down() or c) the event (or another event) is sent up the stack using up_prot.up().
        Overrides:
        up in class Protocol

      • up

        public java.lang.Object up​(Message msg)
        Description copied from class: Protocol
        A single message was received. Protocols may examine the message and do something (e.g. add a header) with it before passing it up.
        Overrides:
        up in class Protocol

      • up

        public void up​(MessageBatch batch)
        Description copied from class: Protocol
        Sends up a multiple messages in a MessageBatch. The sender of the batch is always the same, and so is the destination (null == multicast messages). Messages in a batch can be OOB messages, regular messages, or mixed messages, although the transport itself will create initial MessageBatches that contain only either OOB or regular messages.

        The default processing below sends messages up the stack individually, based on a matching criteria (calling Protocol.accept(org.jgroups.Message)), and - if true - calls Protocol.up(org.jgroups.Event) for that message and removes the message. If the batch is not empty, it is passed up, or else it is dropped.

        Subclasses should check if there are any messages destined for them (e.g. using MessageBatch.getMatchingMessages(short,boolean)), then possibly remove and process them and finally pass the batch up to the next protocol. Protocols can also modify messages in place, e.g. ENCRYPT could decrypt all encrypted messages in the batch, not remove them, and pass the batch up when done.

        Overrides:
        up in class Protocol
        Parameters:
        batch - The message batch

      • providedDownServices

        public java.util.List<java.lang.Integer> providedDownServices()
        Description copied from class: Protocol
        List of events that are provided to layers below (they will be handled when sent from down below)
        Overrides:
        providedDownServices in class Protocol

      • same

        protected static boolean same​(java.util.List<Digest> digests)

      • maxSeqnos

        protected static Digest maxSeqnos​(View view,
                                  java.util.List<Digest> digests)
        Returns a digest which contains, for all members of view, the highest delivered and received seqno of all digests

      • marshal

        protected static Buffer marshal​(java.util.Collection<? extends Address> participants,
                                Digest digest)

      • readParticipantsAndDigest

        protected Tuple<java.util.Collection<? extends Address>,​Digest> readParticipantsAndDigest​(byte[] buffer,
                                                                                                int offset,
                                                                                                int length)