Concurrency – Erlang – dining philosophers error

If the code is hard to follow, I apologize

If anyone is interested, these are instructions: http://www.kth.se/polopoly_fs/1.260940 !/ Menu/general/column-content/attachment/philosophers. pdf

In any case, here is the code, chopsticks process code:

-module(chopstick).
-export([start/0]).

start() ->
spawn_link(fun() -> init() end).
init() ->
available().

available() ->
receive
    {request,From} -> 
        From ! granted,gone();
    quit ->
        ok
        end.
gone() ->
receive
    returned ->
        available();
    quit ->
        ok
        end.

Process code:

-module(eater).
-import(timer,[sleep/1]).
-import(random,[uniform/1]).
-export([start/5,dream/5,eat/5,wait/5]).

start(Hungry,Right,Left,Name,Ctrl) ->
dream(Hungry,Ctrl).

 **%This was wrong,it should say start(Hungry,Ctrl) ->
 spawn_link(fun() -> dream(Hungry,Ctrl) end).**

dream(Hungry,Ctrl) -> 
Time = 500+uniform:random(500),**%This was wrong,it should say random:uniform**
timer:sleep(Time),Right! {request,self()},Left! {request,%skicka {request,self()} till två pinnar
wait(Hungry,Ctrl).

wait(Hungry,Ctrl) ->
receive
    granted ->  
        io:format("~s received a chopstick~n",[Name]),receive
            granted ->
            io:format("~s received a chopstick~n",io:format("~s started eating~n",eat(Hungry,Ctrl)
            end;
    _ -> wait(Hungry,Ctrl)
end.

eat(Hungry,Ctrl) ->
Time = 500+uniform:random(500),Right! returned,Left! returned,io:format("~s put back two chopsticks~n",if 
    Hungry =< 1 ->
        Ctrl ! done;
    true ->
        dream(Hungry-1,Ctrl)
end.

Finally, the moderator process:

-module(dinner).
-export([start/0]).


start() ->
spawn(fun() -> init() end).

init() ->
C1 = chopstick:start(),C2 = chopstick:start(),C3 = chopstick:start(),C4 = chopstick:start(),C5 = chopstick:start(),Ctrl = self(),eater:start(5,C1,C2,"Confucios",Ctrl),**% This is where it crashes**
eater:start(5,C3,"Avicenna",C4,"Plato",C5,"Kant","Descartes",wait(5,[C1,C5]).


wait(0,Chopsticks) ->
lists:foreach(fun(C) -> C ! quit end,Chopsticks);
wait(N,Chopsticks) ->
receive
    done ->
        wait(N-1,Chopsticks);
    abort ->
        erlang:exit(abort)
end.

Output:

11> dinner:start().
<0.85.0>
12> 
=ERROR REPORT==== 10-Nov-2011::02:19:10 ===
 Error in process <0.85.0> with exit value: {undef,[{uniform,random,[500]},{eater,dream,5},{dinner,init,0}]}

Thank you very much. If you've read all this, I haven't learned how to read Erlang's error reports yet If you can and want to tell me what this means, please do it

Solution

I think the problem is that you have three modules: dinner, dinner and chopsticks, but try calling philospher: start with dinner: init / 0 function Try eating: start instead

The second problem is the order of module and function names when generating random numbers; Replace uniform: random: your eater ERL uniform:

1> dinner:start().
<0.35.0>
Confucios received a chopstick
Confucios received a chopstick
Confucios started eating
Confucios put back two chopsticks
Confucios received a chopstick
Confucios received a chopstick
Confucios started eating
Confucios put back two chopsticks
Confucios received a chopstick
Confucios received a chopstick
Confucios started eating
Confucios put back two chopsticks
Confucios received a chopstick
Confucios received a chopstick
Confucios started eating
Confucios put back two chopsticks
Confucios received a chopstick
Confucios received a chopstick
Confucios started eating
Confucios put back two chopsticks
Avicenna received a chopstick
Avicenna received a chopstick
Avicenna started eating
...

This quickly shows the third problem - we should find from the first error report - that the eaters are not actually in their own process So edit eater ERL for the start() function to read:

start(Hungry,Ctrl) ->
    spawn_link(fun() -> dream(Hungry,Ctrl) end).

Now it works as expected:

1> dinner:start().
<0.35.0>
Confucios received a chopstick
Plato received a chopstick
Confucios received a chopstick
Confucios started eating
Descartes received a chopstick
Kant received a chopstick
Confucios put back two chopsticks
Avicenna received a chopstick
...

thank you. It's interesting