Last updated 31.01.12

Before asking questions regarding this exercise, please review the lecture notes of Week #05 (and #06) as well as the documentation on the Erlang web pages.

Multicast

Implement basic multicast, FIFO ordered multicast and Totally ordered multicast in Erlang.

For each of these implement separate Erlang modules that provide the following interface:

minit(NodeID, NodePid, Group)
     called by every node to initialise the underlying multicast
     implementation.  

     NodeID - a unique id for the node
     NodePid - the node's Pid
     Group - a list of Pids of all the nodes in the multicast group

msend(Group, Msg)
     multicast the given message to the group

     Group - a list of Pids of all the nodes in the multicast group
     Msg - the message to send

mreceive()
     wait to receive a multicast message.  This will return a tuple
     {From, Msg} with the next deliverable message that was multicast to
     the group.  The messages returned are ordered according to the
     guarantees provided by the underlying implementation (e.g, no
     ordering, FIFO, total ordering).

An example of using such a module follows (where bmcast.erl implements basic multicast):

do_test(NodeID, Group) ->
    % init the multicast library
    bmcast:minit(NodeID, self(), Group),

    % send some multicasts
    bmcast:msend(Group, NodeID),
    bmcast:msend(Group, NodeID+10),
    bmcast:msend(Group, NodeID+20),

    % receive multicasts from everyone else
    do_receive().


% loop forever trying to receive multicast messages
do_receive() ->
    {From, Msg} = bmcast:mreceive(),
    io:format("received ~w (~w)~n", [Msg, From]),
    do_receive().

You'll notice that Erlang communication is ordered, so in order to really test your implementation you'll want to implement a send function that reorders message sends, for example, by delaying them for a random amount of time.

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