[jboss-jira] [JBoss JIRA] (JGRP-1672) Shared memory to send message between differen processes on the same box

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1672?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12795330#comment-12795330 ] 

Bela Ban commented on JGRP-1672:
--------------------------------

This is only useful for large messages. Also, the currently unsubstantiated claim that message passing via shared memory is faster than via a (loopback) socket (also using shared memory internally) has to be proven first. Especially when sending multicast messages (= to more than one destination).
                
> Shared memory to send message between differen processes on the same box
> ------------------------------------------------------------------------
>
>                 Key: JGRP-1672
>                 URL: https://issues.jboss.org/browse/JGRP-1672
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 3.5
>
>
> Investigate whether it makes sense to use shared memory to pass messages between processes on the same box. Say if we have A, B and C on box-1 and X, Y, Z on box-2, when A multicasts a message, it could loop it back to itself, place it into shared memory for B and C to read and multicast it to X, Y, Z. The multicast socket could be non-loopback, so box-1 would not receive it.
> Problems:
> * Shared memory in Java can only be done via memory mapped (sequential or random access) files. To pass a lot of messages, something like a ring buffer would have to be created in shared memory
> * Unless we use FileLock, or polling/busy reading, there is no way to know when a producer has written a message into shared memory. We'd therefore have to use a signalling mechanism, probably a small JGroups message, to notify the consumer(s) of new messages
> * For multicast messages, we'd have 1 producer but many consumers. A RingBuffer would not work here, as we don't know when all consumers have read a given message, ie. when to advance the read pointer
> ** As an alternative, we could have one shared memory buffer per member on the same host. This would also cater to unicast messages. However, then we'd use up a lot of memory.
> * How would this work for TCP ? We'd have to send the message to only members which are outside the local box. How do we identify those members ?
> * Message reception: a multicast message received and targetted to all members on the same box could also be placed into shared memory, so everyone on the same box receives it
> ** How would this work for TCP ? E.g. A sending a multicast message M would use shared memory to deliver M to B and C on box-1, but if it sends it to X, Y and Z, then that's unneeded work, as it could send it only to X, which could place it into shared memory for Y and Z to consume M.
> *** We'd have to include the knowledge of 'affinity' into an address

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