如果代码很难遵循,我道歉.
这是经典的餐饮哲学家问题,有5位哲学家正在吃饭,但只有5支 – 你需要两只才能吃.
这是经典的餐饮哲学家问题,有5位哲学家正在吃饭,但只有5支 – 你需要两只才能吃.
如果有人有兴趣,这些是说明：
http://www.kth.se/polopoly_fs/1.260940!/Menu/general/column-content/attachment/philosophers.pdf
-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.
哲学家流程代码：
-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,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.
最后是主持人流程：
-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,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.
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,如果你读完所有这些,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,请做.
解决方法
我认为问题在于你有三个模块：晚餐,吃饭和筷子,但是试着打电话给philospher：从晚餐开始：init / 0功能.尝试吃饭：改为开始.
第二个问题是生成随机数时模块和函数名称的顺序;替换制服：随机随机：你的eater.erl制服：
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 ...
这很快就显示了第三个问题 – 我们应该从第一个错误报告中发现 – 食者实际上并不在他们自己的过程中.所以编辑eater.erl以便start()函数读取：
start(Hungry,Ctrl) ->
spawn_link(fun() -> dream(Hungry,Ctrl) end).
现在它按预期工作：
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.这很有趣.
