[jboss-jira] [JBoss JIRA] Commented: (JGRP-815) Scatter/Gather to avoid copying

[Bela Ban (JIRA)]

    [ https://jira.jboss.org/jira/browse/JGRP-815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12430576#action_12430576 ] 

Bela Ban commented on JGRP-815:
-------------------------------

Looks like we have to wait for JDK 7 (NIO.2): http://jcp.org/en/jsr/detail?id=203

> Scatter/Gather to avoid copying
> -------------------------------
>
>                 Key: JGRP-815
>                 URL: https://jira.jboss.org/jira/browse/JGRP-815
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 2.8
>
>
> 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).

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