Package org.jgroups.protocols

Class FRAG

  • public class FRAG
extends Protocol
    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 Message.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.

    Author:
    Bela Ban, Filip Hanik

    • Constructor Detail

      • FRAG

        public FRAG()

    • Method Detail

      • getFragSize

        public int getFragSize()

      • setFragSize

        public void setFragSize​(int s)

      • getNumberOfSentMessages

        public long getNumberOfSentMessages()

      • getNumberOfSentFragments

        public long getNumberOfSentFragments()

      • getNumberOfReceivedMessages

        public long getNumberOfReceivedMessages()

      • getNumberOfReceivedFragments

        public long getNumberOfReceivedFragments()

      • init

        public void init()
          throws java.lang.Exception
        Description copied from class: Protocol
        Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.
        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 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(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