拖延是行不通的

Question

我正在制作一个活动日历，作为学校的一项任务，我对此并不陌生。问题是，当我对循环中的接收部分执行延迟时，我的表就会消失。我在互联网上和我的代码中查找错误2天。

事件是一个元组=> {Time (tuple类似于now()、make_ref()}、NotifyPid、Load} ) getTime通常会返回一个整数

-module(calender).
-export([start/0, start_new/0, post/1, postincr/1, gettime/0]).
-export ([kalender/0, getTime/1, increment/1, makeTime/1]). % internal use only

%% @doc Starts the program
start() ->
    case whereis('event manager') =:= undefined of
        true ->
            register('event manager', spawn(calender, kalender, [])),
            {ok, 'event manager'};
        false ->
            {event_not_made}
    end.

%% @doc Starts a new program even program already exist but kills it first
start_new() ->
    case whereis('event manager') =:= undefined orelse unregister('event manager') of
        true ->
            ets:delete(calend),
            register('event manager', spawn(calender, kalender, [])),
            {ok, 'event manager'};
        false ->
            {ok, event_not_made}
    end.

% Puts Events into sorted table
% Time is an integer value in milliseconds  
post(Event) ->
    'event manager'!{post, Event},
    {ok, gettime()}.

%% @doc Puts Events into sorted table
%% Increment is an integer value which will be added to the present time
%% The increment value of time is in milliseconds
%% @end
postincr(Event) ->
    'event manager'!{postincr, Event},
    {ok, gettime()}.

%% @doc Gives the difference in time between present and time at start
gettime() ->
    'event manager'!{gettime, self()},
    receive
        T -> T
    end.

%% @private Calculates the difference of time between the present time and Event time
getTime(Time) ->
    NowTime = now(),
    timer:now_diff(Time, NowTime)div 1000.

%% @private Adds the incremental time of postincr to the present time
increment(Incr) ->
    {X, Y, Z} = now(),
    X1 = X * 1000000000000,
    Y1 = Y * 1000000,
    Incr1 = X1 + Y1 + Z + (Incr * 1000),
    makeTime(Incr1).

%% @private Changes integer to tuple of 3 values
makeTime(Time) ->
    X = Time div 1000000000000,
    Y = (Time rem 1000000000000) div 1000000,
    Z = Time rem 1000000,
    {X, Y, Z}.

%% @private Makes the sorted table, starts the loop
kalender() ->
    Cal = {ets:new(calend, [ordered_set, named_table, {keypos, 1}, public]), now()},
    loop(Cal).

%% @private Loops through the table and checks for received messages
loop(Cal) ->
    io:format("Loop start ~n"),
    {Calen, TimeAtStart} = Cal,

    io:format("Before case ~n"),
    case ets:first(Calen)  of
        '$end_of_table' ->
            io:format("end of table ~n"),
            {end_of_table};
        {Time, Ref} ->
            io:format("Before calculation event ~n"),
            Ms = getTime(Time),
            io:format("After getTime ~n"),
            if 
                Ms =< 0 ->
                    io:format("Ms =< 0 ~n"),
                    [Event | _Rest] = ets:lookup(Calen, {Time, Ref}),
                    io:format("~p~n", [Event]),
                    {{_Time1, _Ref1}, NotifyPid, _Load} = Event,
                    io:format("~p~n", [NotifyPid]),
                    NotifyPid!Event,
                    io:format("After event send ~n"),
                    ets:delete(Calen, {Time, Ref}),
                    io:format("After Ms =< 0 ~n");
                Ms > 0 ->
                    io:format("Event not done ~n"),
                    {event_not_yet_done}
            end,
            io:format("After calculation event ~n")
    end,

我认为从这里开始就出了问题：

io:format("Before Delay ~n"),
        % Gets the delay time
        Delay = case ets:first(Calen) of
            '$end_of_table' ->
                io:format("Delay infinity ~n"),
                infinity;
            {DelayTime, _DelayRef} ->
                io:format("~p~n", [DelayTime]), => the DelayTime has for example a value of {9283,823031,155000}

                Dl = getTime(DelayTime),
                case Dl > 0 of
                    true ->
                        Dl,
                        io:format("~p~n", [Dl]); => this io:format gives me on the screen a calculated value example: 7899995274337

                    false ->
                        0,
                        io:format("0 ~n")
                end,
                io:format("Delay time~n")
        end,

        io:format("Before receive ~n"),
        receive
            {post, PostEvent} -> 
                io:format("In post ~n"),
                {PostTimeI, Np, Ld} = PostEvent,
                PostRef = make_ref(),
                PostTimeT = makeTime((PostTimeI * 1000)),
                io:format("After making the tuples ~n"),
                io:format("~p   ~p  ~p  ~p  ~p~n", [PostTimeI, PostRef, PostTimeT, Np, Ld]),
                ets:insert(Calen, {{PostTimeT, PostRef}, Np, Ld}),
                io:format("After insert post ~p~n", [whereis('event manager')]);
            {postincr, PostIncrEvent} ->
                {Incr, Np, Ld} = PostIncrEvent,
                PostIncrRef = make_ref(),
                PostIncrTime = increment(Incr),
                ets:insert(Calen, {{PostIncrTime, PostIncrRef}, Np, Ld});
            {gettime, From} ->
                From!getTime(TimeAtStart)
            after
                Delay ->
                    io:format("Delaying ~n"),
                    {ok}
        end,
        io:format("After receive ~n"),
        loop(Cal).

Answer 1

我发现了我的问题:我正在测试我的代码，但是我没有Pid来测试，所以我使用了whereis('event manager')。相反，我不得不使用self()。

Answer 2

问题可能是您的进程产生了start/0函数崩溃。当进程崩溃时，它拥有的任何ETS表都会被收获。尝试使用spawn_monitor，然后使用shell的刷新()命令来获取传入的消息。它可能会死。另一种方法是使用proc_lib模块中的工具，然后使用erl -boot start_sasl获得一些基本的崩溃错误报告，并为您的流程运行。

“裸露”的spawn(...)通常是危险的，因为如果产生的进程崩溃，您将什么也学不到。至少使用spawn_link或spawn_monitor。