为什么这个 gen_statem 呼叫阻塞？

Question

你好，我想弄清楚在使用 gen_statem 时为什么调用会阻塞，因为我的 fsm 运行在一个单独的进程中。

-module(fsm).
-record(data,{
    current="None",
    intvCount=0,
    jobCount=0
}).
-export([init/1,terminate/3,callback_mode/0,code_change/4]).

-export([state/1,start/0,interview/2,reject/2,wait/1]).

-export([sitting_home/3,interviewing/3]).
-export([handle_event/3]).
-behaviour(gen_statem).

handle_event({call,From},get_state,Data)->
    io:format("why you need state>"),
    {keep_state,Data};
handle_event({call,From},Event,Data)->
    {keep,state,Data}.
%API
start()->
    gen_statem:start_link(?MODULE,[],[]).
state(PID)->
    gen_statem:call(PID,get_state).

interview(PID,Company)->
    gen_statem:call(PID,{intv,Company}).
reject(PID,Company)->
    gen_statem:call(PID,{reject,Company}).
wait(PID)->
    gen_statem:call(PID,{wait}).

%mandatory
code_change(V,State,Data,Extra)->{ok,State,Data}.
callback_mode() ->
    state_functions.
init([])->
    {ok,sitting_home,#data{current="None",jobCount=0,intvCount=0}}.
terminate(Reasom,State,Data)->
    void.

% State implementations

sitting_home({call,From},{intv,Company},Data=#data{intvCount=C})->
    io:format("called for interview"),
    {next_state,interviewing,Data#data{intvCount=C+1},{reply,From,something}};
sitting_home({call,From},Event,Data)->
    {keep_state,Data}.

interviewing({call,From},{rejected,Company},Data)->
    {next_state,sitting_home,Data,{reply,From,somethingelse}};
interviewing({call,From},wait,Data)->
    {keep_state,Data}.

用法:

>{ok,Pid}=fsm:start().
>fsm:state(). //blocks !

>{ok,Pid}=fsm:start().
>fsm:interview(Pid).
 called for interview %and blocks

为什么两个调用都阻塞？除了 shell 之外，我正在生成一个不同的进程，其中 fsm 使用 gen_statem:start_link 运行。为什么在这两种情况下它都会阻塞？

更新在有人指出我忘记使用 reply 以便将某些内容发送回 caller.However 之后，我更新了我的 post，即使以这种形式，handle_event/3 仍然会阻塞：

handle_event({call,From},get_state,Data)->
    {keep_state,Data,[{reply,From,Data}]}.

Answer 1

因为那是 gen_statem:call 所做的：

Makes a synchronous call to the gen_statem ServerRef by sending a request and waiting until its reply arrives

并且您的状态函数不发送任何回复。它们应该看起来像

sitting_home({call,From},{intv,Company},Data=#data{intvCount=C})->
    io:format("called for interview"), 
    {next_state,interviewing,Data#data{intvCount=C+1},{reply,From,WhateverReplyYouWant}};

或

sitting_home({call,From},{intv,Company},Data=#data{intvCount=C})->
    io:format("called for interview"), 
    gen_statem:reply(From, WhateverReplyYouWant),
    {next_state,interviewing,Data#data{intvCount=C+1}};

如果没有有用的回复，请考虑

使用 cast 而不是 call（并将 cast 作为状态函数中的 EventType 处理），或
ok作为回复。

为什么这个 gen_statem 呼叫阻塞？

Why is this gen_statem call blocking?

erlang

fsm