concurrency - Erlang-餐饮哲学家的错误

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已关闭8年。




如果代码难以理解，我深表歉意。
这是经典的用餐哲学家问题，有5位哲学家在吃饭，但只有5条棍棒-您需要吃2根。

这些是说明，如果有人感兴趣的话:
http://www.kth.se/polopoly_fs/1.260940!/Menu/general/column-content/attachment/philosophers.pdf

无论如何，这是代码，筷子处理代码:

-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.

哲学家的程序代码:

-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, Right, Left, Name, Ctrl).

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

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

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

eat(Hungry, Right, Left, Name, Ctrl) ->
Time = 500+uniform:random(500), **%This was wrong, it should say random:uniform**
timer:sleep(Time),
Right! returned,
Left! returned,
io:format("~s put back two chopsticks~n", [Name]),
if
    Hungry =< 1 ->
        Ctrl ! done;
    true ->
        dream(Hungry-1, Right, Left, Name, Ctrl)
end.

最后是主机进程:

-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, C2, C3, "Avicenna", Ctrl),
eater:start(5, C3, C4, "Plato", Ctrl),
eater:start(5, C4, C5, "Kant", Ctrl),
eater:start(5, C5, C1, "Descartes", Ctrl),
wait(5, [C1, C2, C3, C4, 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.

输出:

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}]}

非常感谢您甚至阅读了所有这些内容，但我还没有学会如何阅读erlang的错误报告。如果可以，并想告诉我这意味着什么，请执行。

最佳答案

我认为问题在于您有三个模块:dinner，eater和chopstick，但是尝试在philospher:start函数中调用dinner:init/0。请尝试eater:start。

第二个问题是生成随机数时模块和函数名称的顺序。将uniform:random中的random:uniform替换为eater.erl:

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
...

这很快显示出第三个问题-我们应该从第一个错误报告中发现-食用者实际上不在他们自己的过程中。因此，编辑eater.erl，以便start()函数读取:

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

现在，它可以按预期工作:

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
...

谢谢。这很好玩。

关于concurrency - Erlang-餐饮哲学家的错误，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/8073878/