Package org.jgroups.protocols

Class FRAG4

java.lang.Object
org.jgroups.stack.Protocol
org.jgroups.protocols.Fragmentation
org.jgroups.protocols.FRAG2
org.jgroups.protocols.FRAG4
All Implemented Interfaces:
Lifecycle
public class FRAG4 extends FRAG2
Fragmentation layer. Fragments messages larger than frag_size into smaller packets. Reassembles fragmented packets into bigger ones. The fragmentation ID is added to the messages as a header (and removed at the receiving side).

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 (monotonically increasing) and (c) the fragement ID which ranges from 0 to number_of_fragments-1.

Requirement: lossless delivery (e.g. NAKACK2, UNICAST3). No requirement on ordering. Works for both unicast and multicast messages.

Compared to FRAG2, this protocol does not need to serialize the message in order to break it into smaller fragments: if the message is a BytesMessage, then we send all fragments with a reference to the original message's byte array, plus and offset and length. Otherwise, we use a number of FragmentedMessage instances, with a reference to the original message and also an offset and length. These serialize messages at the last possible moment, just before being sent by the transport.

Version:
5.0

  • Constructor Details

    • FRAG4

      public FRAG4()

  • Method Details

    • fragment

      protected void fragment(Message msg)
      Description copied from class: FRAG2
      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}
      Overrides:
      fragment in class FRAG2

    • assembleMessage

      protected Message assembleMessage(Message[] fragments, boolean needs_deserialization, FragHeader hdr) throws Exception
      Description copied from class: FRAG2
      Assembles all the message fragments into one message. This method does not check if the fragmentation is complete (use FRAG2.FragEntry.isComplete() to verify) before calling this method)
      Overrides:
      assembleMessage in class FRAG2
      Returns:
      the complete message
      Throws:
      Exception