【发布时间】：2016-06-19 09:32:37
【问题描述】：
我正在尝试为著名的 Dijkstra 的餐饮哲学家问题实施我自己的解决方案。我得到的只是状态机，哲学家应该同时抓住两个叉子。
这是我的代码：
-module(assess3).
-compile([export_all]).
-define(EAT,1000).
-define(THINK,1000).
college() ->
R = spawn_link(?MODULE, report,[]),
F1 = spawn_link(?MODULE, fork,["fork1",R]),
F2 = spawn_link(?MODULE, fork,["fork2",R]),
F3 = spawn_link(?MODULE, fork,["fork3",R]),
F4 = spawn_link(?MODULE, fork,["fork4",R]),
F5 = spawn_link(?MODULE, fork,["fork5",R]),
spawn_link(?MODULE, philosopher,["Socrates", R, F1,F2]),
spawn_link(?MODULE, philosopher,["Confucius", R, F2,F3]),
spawn_link(?MODULE, philosopher,["Aristole", R, F3,F4]),
spawn_link(?MODULE, philosopher,["Homer", R, F4,F5]),
spawn_link(?MODULE, sphilosopher,["Plato", R, F1,F5]).
%%create philosophers randomly
philosopher(Name, Report, LeftF, RightF) ->
random:seed(erlang:phash2([node()]),
erlang:monotonic_time(),erlang:unique_integer()),
create_phils(Name,Report,LeftF,RightF).
%%create special philosopher
sphilosopher(Name, Report, RightF, LeftF) ->
random:seed(erlang:phash2([node()]),
erlang:monotonic_time(),erlang:unique_integer()),
create_special_phil(Name,Report,RightF,LeftF).
%%creates random 4 philosophers who get the Left fork first then the right fork
create_phils(Name,Report,LeftF,RightF) ->
%%thinking state
reporting(Name,Report,thinking),
timer:sleep(random:uniform(?THINK)),
%%hungry state
reporting(Name,Report,hungry),
LeftF ! RightF! {pick,self()},
receive
{pick, LeftF} -> reporting(Report, Name, left);
{pick, RightF} -> reporting(Report, Name, right)
end,
receive
{pick, LeftF} -> reporting(Report, Name, left);
{pick, RightF} -> reporting(Report, Name, right)
end,
%%eating state
reporting(Report,Name,eating),
timer:sleep(random:uniform(?EAT)),
LeftF ! RightF ! {let_go,self()},
create_phils(Name,Report,LeftF,RightF).
%%create special philosopher who attempts to communicate first with the
%%right fork proccess instead of the left fork
create_special_phil(Name,Report,RightF,LeftF) ->
%%thinking state
reporting(Name,Report,thinking),
timer:sleep(random:uniform(?THINK)),
%%hungry state
reporting(Name,Report,hungry),
RightF ! LeftF ! {pick,self()},
receive
{pick, RightF} -> reporting(Report, Name, right);
{pick, LeftF} -> reporting(Report, Name, left)
end,
receive
{pick, RightF} -> reporting(Report, Name, right);
{pick, LeftF} -> reporting(Report, Name, left)
end,
%%eating state
reporting(Report,Name,eating),
timer:sleep(random:uniform(?EAT)),
RightF ! LeftF ! {let_go,self()},
create_special_phil(Name,Report,RightF,LeftF).
%%prepares what the Report proccess will print
reporting(Name,Report,Status) ->
Report ! {Name,Status,self()},
receive
{Report,ack} -> true
end.
%%Report proccess, receives and prints
report() ->
receive
{Name,Status, Pid} ->
io:format("~s : ~s ~n",[Name,status(Status)]),
Pid ! {ack,self()},
report()
end.
%%function to pass the appropriate status in string for io:format
status(Status) ->
case Status of
thinking -> "is thinking";
hungry -> "is hungry";
eating -> "is eating";
right -> "got right fork";
left -> "got left fork";
on_table -> "on table";
in_use ->"in use";
Status -> atom_to_list(Status)
end.
fork(Name,Report) ->
receive
{picked,Pid} ->
reporting(Report,Name,in_use),
Pid ! {picked,self()},
receive
{let_go,Pid} ->
reporting(Report,Name,on_table)
end,
fork(Name,Report)
end.
我没有收到任何错误，但是当我尝试在 Erlang shell 中运行 assess3:college(). 时，我看到的只是进程通信，而不是：
苏格拉底：在思考
孔子：在想
亚里士多德：在思考
荷马：在思考
柏拉图：在思考
我不明白为什么会发生这种情况，因为在我开始编码之前，我都是手工设计的，以避免迷路。任何帮助表示赞赏。
PS。这个实现应该防止死锁，因为四个哲学家先抓住左叉，第五个尝试先选择右叉，尽管我知道这可能会导致资源匮乏，这意味着一个哲学家可能永远不会吃东西。我暂时不关心这个——一次一步。
【问题讨论】：
标签： concurrency erlang