Package org.jgroups.protocols

Class SEQUENCER

  • All Implemented Interfaces:
    Lifecycle
    public class SEQUENCER
extends Protocol
    Implementation of total order protocol using a sequencer. Consult SEQUENCER.txt for details
    Author:
    Bela Ban

    • Field Detail

      • coord

        protected volatile Address coord

      • view

        protected volatile View view

      • is_coord

        protected volatile boolean is_coord

      • seqno

        protected final java.util.concurrent.atomic.AtomicLong seqno

      • forward_table

        protected final java.util.NavigableMap<java.lang.Long,​Message> forward_table
        Maintains messages forwarded to the coord which which no ack has been received yet. Needs to be sorted so we resend them in the right order

      • send_lock

        protected final java.util.concurrent.locks.Lock send_lock

      • send_cond

        protected final java.util.concurrent.locks.Condition send_cond

      • ack_mode

        protected volatile boolean ack_mode
        When ack_mode is set, we need to wait for an ack for each forwarded message until we can send the next one

      • flushing

        protected volatile boolean flushing
        Set when we block all sending threads to resend all messages from forward_table

      • running

        protected volatile boolean running

      • in_flight_sends

        protected final java.util.concurrent.atomic.AtomicInteger in_flight_sends
        Keeps track of the threads sending messages

      • delivery_table

        protected final java.util.concurrent.ConcurrentMap<Address,​BoundedHashMap<java.lang.Long,​java.lang.Long>> delivery_table

      • ack_promise

        protected final Promise<java.lang.Long> ack_promise
        Used for each resent message to wait until the message has been received

      • delivery_table_max_size

        protected int delivery_table_max_size

      • threshold

        protected int threshold

      • flush_forward_table

        protected boolean flush_forward_table

      • num_acks

        protected int num_acks

      • forwarded_msgs

        protected long forwarded_msgs

      • bcast_msgs

        protected long bcast_msgs

      • received_forwards

        protected long received_forwards

      • received_bcasts

        protected long received_bcasts

      • delivered_bcasts

        protected long delivered_bcasts

    • Constructor Detail

      • SEQUENCER

        public SEQUENCER()

    • Method Detail

      • isCoordinator

        public boolean isCoordinator()

      • getCoordinator

        public Address getCoordinator()

      • getForwardTableSize

        public int getForwardTableSize()

      • setThreshold

        public SEQUENCER setThreshold​(int new_threshold)

      • setDeliveryTableMaxSize

        public SEQUENCER setDeliveryTableMaxSize​(int size)

      • init

        public void init()
          throws java.lang.Exception
        Description copied from class: Protocol
        Called after a protocol has been created and before the protocol is started. Attributes are already set. Other protocols are not yet connected and events cannot yet be sent.
        Specified by:
        init in interface Lifecycle
        Overrides:
        init in class Protocol
        Throws:
        java.lang.Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the the channel constructor will throw an exception

      • 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 ready to receive events. Will be called from bottom to top.
        Specified by:
        start in interface Lifecycle
        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

      • 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(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.iterator(Predicate)), 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

      • handleViewChange

        protected void handleViewChange​(View v)

      • flush

        protected void flush​(Address new_coord)
              throws java.lang.InterruptedException
        Throws:
        java.lang.InterruptedException

      • flushMessagesInForwardTable

        protected void flushMessagesInForwardTable()
        Sends all messages currently in forward_table to the new coordinator (changing the dest field). This needs to be done, so the underlying reliable unicast protocol (e.g. UNICAST) adds these messages to its retransmission mechanism
        Note that we need to resend the messages in order of their seqnos! We also need to prevent other message from being inserted until we're done, that's why there's synchronization.
        Access to the forward_table doesn't need to be synchronized as there won't be any insertions during flushing (all down-threads are blocked)

      • forwardToCoord

        protected void forwardToCoord​(long seqno,
                              Message msg)

      • forward

        protected void forward​(Message msg,
                       long seqno,
                       boolean flush)

      • broadcast

        protected void broadcast​(Message msg,
                         boolean copy,
                         Address original_sender,
                         long seqno,
                         boolean resend)

      • unwrapAndDeliver

        protected void unwrapAndDeliver​(Message msg,
                                boolean flush_ack)
        Unmarshal the original message (in the payload) and then pass it up (unless already delivered)

      • canDeliver

        protected boolean canDeliver​(Address sender,
                             long seqno)
        Checks if seqno has already been received from sender. This weeds out duplicates. Note that this method is never called concurrently for the same sender, as the sender in NAKACK will always be the coordinator.

      • block

        protected void block()

      • unblockAll

        protected void unblockAll()

      • startFlusher

        protected void startFlusher​(Address new_coord)

      • stopFlusher

        protected void stopFlusher()