Package org.jgroups.protocols

Class FRAG

  • All Implemented Interfaces:
    Lifecycle
    public class FRAG
extends Fragmentation
    Fragmentation layer. Fragments messages larger than FRAG_SIZE into smaller packets. Reassembles fragmented packets into bigger ones. The fragmentation number is added to the messages as a header (and removed at the receiving side).

    Contrary to FRAG2, FRAG marshals the entire message (including the headers) into a byte[] buffer and the fragments that buffer. Because BaseMessage.size() is called rather than Message.getLength(), and because of the overhead of marshalling, this will be slower than FRAG2.

    Each fragment is identified by (a) the sender (part of the message to which the header is appended), (b) the fragmentation ID (which is unique per FRAG layer (monotonically increasing) and (c) the fragement ID which ranges from 0 to number_of_fragments-1.

    Requirement: lossless delivery (e.g. NAK, ACK). No requirement on ordering. Works for both unicast and multicast messages.

    • Field Detail

      • fragment_list

        protected final FRAG.FragmentationList fragment_list
        Contains a frag table per sender, this way it becomes easier to clean up if a sender leaves or crashes

      • curr_id

        protected final java.util.concurrent.atomic.AtomicInteger curr_id

      • members

        protected final java.util.List<Address> members

      • HAS_FRAG_HEADER

        protected final java.util.function.Predicate<Message> HAS_FRAG_HEADER

      • num_sent_msgs

        long num_sent_msgs

      • num_received_msgs

        long num_received_msgs

    • Constructor Detail

      • FRAG

        public FRAG()

    • Method Detail

      • getNumberOfSentMessages

        public long getNumberOfSentMessages()

      • getNumberOfReceivedMessages

        public long getNumberOfReceivedMessages()

      • 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

      • down

        public java.lang.Object down​(Event evt)
        Fragment a packet if larger than frag_size (add a header). Otherwise just pass down. Only add a header if framentation is needed !
        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)
        If event is a message, if it is fragmented, re-assemble fragments into big message and pass up the stack.
        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#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

      • handleViewChange

        private void handleViewChange​(View view)

      • fragment

        private void fragment​(Message msg)
        Send all fragments as separate messages (with same ID !). Example: 
         Given the generated ID is 2344, number of fragments=3, message {dst,src,buf}
 would be fragmented into:
 
        
 [2344,3,0]{dst,src,buf1},
 [2344,3,1]{dst,src,buf2} and
 [2344,3,2]{dst,src,buf3}

      • unfragment

        private Message unfragment​(Message msg,
                           FragHeader hdr)
        1. Get all the fragment buffers 2. When all are received -> Assemble them into one big buffer 3. Read headers and byte buffer from big buffer 4. Set headers and buffer in msg 5. Pass msg up the stack