Assignment 2

Due Date: February, 16 2012

For this assignment, you will use Erlang to implement the dining philosophers problem and samefringe.

Erlang is available on the departmental machines, but you can download a copy for yourself from here. A quick overview on how to get started with Erlang is available here.

Part I

Implement the samefringe problem in Erlang. Given two trees (represented as lists), your program should create two threads, each one responsible for traversing one of the trees, communicating with one another using Erlang message-passing primitives. Each thread traverses its respective tree until its encounters an integer leaf node. One of the threads (the master) communicates its leaf to the other (the slave); if they match, an acknowledgement is sent, and both threads continue their traversal. If they do not, a message is sent to terminate the search.

Part 2

For this part of the assignment, you will implement the dining philosophers problem in Erlang. The code structure for some of the procedures is given below. You will need to fill in the code for fork(),room(), and philosophers(). Recall each philosopher thinks, enters the room to eat, picks up the forks on his left and right, eats, puts down the two forks, and exits. Observe that each of these entities are represented as Erlang processes.


start(N) ->

   Control = spawn(fun () ->

     Room = spawn_link(fun () -> room(0, N - 1) end),

     Fork = spawn_link(fun fork/0),

     setup(N, Room, Fork, Fork)

   end),

   register(dining_philosophers, Control),

 ok.



setup(N, Room, Left, Last) when N > 1 ->

   Right = spawn_link(fun fork/0),

   spawn_link(fun () -> philosopher(N, Room, Left, Right) end),

   setup(N - 1, Room, Right, Last);



setup(1, Room, Left, Right) ->

    spawn_link(fun () -> philosopher(1, Room, Left, Right) end),

    receive

      _ -> exit({done})

    end.



stop() ->

    dining_philosophers ! stop,

    unregister(dining_philosophers),

    ok.



pause(Milliseconds) ->

    receive after Milliseconds -> ok end.



say(Name, Pred) -> 

    io:format("Philosopher ~w ~s~n", [Name, Pred]).



eat(Name) ->

    say(Name, "is eating."),

    pause(3000).



think(Name) ->

    say(Name, "is thinking."),

    pause(500).