Scatter/Gather to avoid copying ------------------------------- Key: JGRP-815 URL: https://issues.redhat.com/browse/JGRP-815 Project: JGroups Issue Type: Sub-task Reporter: Bela Ban Assignee: Bela Ban Priority: Major Fix For: 5.0.0.Alpha5 Attachments: bla10.java, bla9.java When we invoke Channel.send(), we pass a bufffer to JGroups. At the transport level, JGroups marshals the sender and destination address, plus all headers and the buffer into a new byte[] buffer, which is then passed to the socket (DatagramSocket, MulticastSocket, Socket). We cannot do gathering writes on a DatagramSocket because DatagramSocket doesn't expose this functionality, contrary to a DatagramChannel. We could avoid having to copy the user's buffer by using gathering writes: effectively passing to the socket NIO ByteBuffers containing: 1: Src and dest address plus flags, plus possibly size 2: The marshalled headers 3: The buffer passed to JGroups by the user We can obtain a gathering-write channel as follows: ByteBuffer[] buffers; // contains the 3 byte buffers above DatagramSocket sock; DatagramChannel ch=sock.getChannel(); ch.write(buffers, 0, length); // length is the number of bytes of the total marshalled message This is supported by a GatheringByteChannel. I don't think there's currently a need to do scattered reads, but this needs to get investigated more. Also investigate whether MulticastSockets support gathering writes (whether they expose the correct DatagramChannel).