（我的实现）进程不通信

Question

我正试图为著名的Dijkstra餐厅哲学家问题实现我自己的解决方案。我得到的只是状态机，一个哲学家应该同时抓住这两个叉子。

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.

除了尝试运行assess3:college（）时，我没有收到任何错误在Erlang shell中，我看到的不是进程通信，而是：

苏格拉底是思考吗？孔子是思考吗

我不明白为什么会发生这种情况，因为在我开始编码之前，为了避免迷路，我手工设计了一切。任何帮助赞赏。

这个实现应该是为了防止死锁，因为四个哲学家首先抓住左边的叉子，第五个哲学家则试图首先抓住右边的叉子，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。我现在不在乎这个，一步一个脚印。

Answer 1

您有几个与不匹配的消息和顺序错误的函数参数相关的问题。不匹配的消息会导致东西永远挂起等待从未发送的消息。由于错误的参数问题，修复这些问题会导致崩溃。

例如，考虑您的代码> For < /Cult>函数：

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.

它在等待一个{选择的，...}消息，但是你的哲学家正在发送{选择，...}消息，它用一个{选择的，...}消息回复，但是哲学家希望收到{选择，...}消息。

查看您的报告功能：

report() ->
    receive
        {Name,Status, Pid} ->
            io:format("~s : ~s ~n",[Name,status(Status)]),
            Pid ! {ack,self()},
            report()
    end.

它将{ack，self（）}消息发送回Pid，但这些进程需要{Report，ack}消息。

在许多您称之为报告（报告、名称等）的地方 其中报告和名称参数顺序错误。

这里有一个固定的版本，似乎工作。

-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
        {picked, LeftF} -> reporting(Name, Report, left);
        {picked, RightF} -> reporting(Name, Report, right)
    end,
    receive
        {picked, LeftF} -> reporting(Name, Report, left);
        {picked, RightF} -> reporting(Name, Report, right)
    end,
    %%eating state
    reporting(Name,Report,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
        {picked, RightF} -> reporting(Name, Report, right);
        {picked, LeftF} -> reporting(Name, Report, left)
    end,
    receive
        {picked, RightF} -> reporting(Name, Report, right);
        {picked, LeftF} -> reporting(Name, Report, left)
    end,
    %%eating state
    reporting(Name,Report,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} -> ok
    end.

%%Report proccess, receives and prints
report() ->
    receive
        {Name,Status,Pid} ->
            io:format("~s : ~s ~n",[Name,status(Status)]),
            Pid ! {self(),ack},
            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
        {pick,Pid} ->
            reporting(Name,Report,in_use),
            Pid ! {picked,self()},

            receive
                {let_go,Pid} ->
                    reporting(Name,Report,on_table)
            end,
            fork(Name,Report)
    end.