multithreading - Erlang计时器:sleep(1000) cause dead in thread

Question

我用Erlang编写了一个代码，并使用了timer.sleep()，但是当我编写timer.sleep(100)时，它是不错的，并且可以正常工作，但是我需要更多的时间来停止线程以及增加时间并运行计时器。使用spawn调用的函数中的sleep(100)，然后代码不起作用。

在代码中，第二个io不在控制台中打印，因此该线程在时间time:sleep(1000)中死了。

request_handler ( Name, Amount, Banks ) ->
  io:format("~p ~p ~p ~n", [Name, Amount, Banks]),
  timer:sleep(1000),
  io:format("~p ~p ~p ~n", [Name, Amount, Banks]),
  if Amount < 50 ->
    Ask_amount = rand:uniform(Amount);
  true ->
    Ask_amount = rand:uniform(50)
    end,
  Bank = lists:nth(rand:uniform(length(Banks)), Banks),
  Pid = whereis(Bank),
  Pid ! {self(), Ask_amount},
  receive
    {accept, Ask_amount} ->
      request_handler(Name, (Amount - Ask_amount), Banks);
    {reject} ->
      request_handler(Name, Amount, lists:filter(fun (Elem) -> not lists:member(Elem, [Bank]) end, Banks ))
  end.

任何人都知道我怎样才能使erlang中的线程休眠1000毫秒？

Answer 1

In the code the second io does not print in console, so the thread dead in the line time:sleep(1000).

首先，在erlang中，我们称它们为进程，而不是线程。如果正在运行 handle_request()的进程在 sleep 时死亡，即在第二个format语句显示任何输出之前，则应该在某处看到错误消息。

您没有提供足够的信息来帮助您。您的问题本质上是这样的:

I have the following function running in a process:

go() ->
    io:format("hello"),
    timer:sleep(1000),
    io:format("goodbye").

I don't see the second output. Why is my process dying during the sleep?

答案是:因为某些东西杀死了您的过程。

这是一个示例，显示了如何使 request_handler()进程休眠1秒:

handlers.erl:

-module(handlers).
-compile([export_all]).

request_handler ( Name, Amount, Banks ) ->
    io:format("Format1: ~p ~p ~p ~n", [Name, Amount, Banks]),
    timer:sleep(1000),
    io:format("Format2: ~p ~p ~p ~n", [Name, Amount, Banks]),

    % This is how you write an if statement when you want to assign
    % the result to a variable:
    AskAmount = if 
                    Amount < 50 -> rand:uniform(Amount);
                    true        -> rand:uniform(50)
                end,
    Bank = lists:nth(rand:uniform(length(Banks)), Banks),
    Pid = whereis(Bank),
    Pid ! {self(), AskAmount},

    receive
        {accept, AskAmount} ->
            request_handler(Name, (Amount - AskAmount), Banks);
        {reject} ->
            request_handler(
                Name, 
                Amount, 
                lists:filter(fun (Elem) -> not lists:member(Elem, [Bank]) end, 
                             Banks 
                )
             )
    end.        

上面的if语句编写方式将摆脱警告:

Warning: variable 'Ask_amount' exported from 'if

bank.erl:

-module(bank).
-compile(export_all).

init(Name) ->
    register(Name, spawn(?MODULE, loop, [ok])).

loop(State) ->
    receive
        {From, Amount} ->
            From ! {accept, Amount},
            loop(State)
    end.

create_banks(Names) ->
    lists:foreach(
        fun(Name) -> init(Name) end,
        Names  %=> [bank1, bank2, bank3]
    ).

my.erl:

-module(my).
-compile([export_all]).

go() ->
    BankNames = [bank1, bank2, bank3],
    bank:create_banks(BankNames),
    handlers:request_handler("Hello", 500, BankNames).

在 shell 中:

~/erlang_programs$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3  (abort with ^G)

1> c(bank).    
bank.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,bank}

2> c(handlers).
handlers.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,handlers}

3> c(my).      
my.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,my}

4> my:go().    
Format1: "Hello" 500 [bank1,bank2,bank3] 
Format2: "Hello" 500 [bank1,bank2,bank3] 
Format1: "Hello" 499 [bank1,bank2,bank3] 
Format2: "Hello" 499 [bank1,bank2,bank3] 
Format1: "Hello" 488 [bank1,bank2,bank3] 
Format2: "Hello" 488 [bank1,bank2,bank3] 
Format1: "Hello" 468 [bank1,bank2,bank3] 
Format2: "Hello" 468 [bank1,bank2,bank3] 
Format1: "Hello" 460 [bank1,bank2,bank3] 
Format2: "Hello" 460 [bank1,bank2,bank3] 
Format1: "Hello" 456 [bank1,bank2,bank3] 
Format2: "Hello" 456 [bank1,bank2,bank3] 
Format1: "Hello" 419 [bank1,bank2,bank3] 
...
...
^C^C

对评论的回复:

I want to run function 'request_handler' more than one time concurrently. ...but when I run the request handler:

spawn(handlers, request_handler, [hello, 450, Banks])

the second io not working.

这个对我有用:

-module(my).
-compile([export_all]).

go() ->
    BankNames = [bank1, bank2, bank3],
    bank:create_banks(BankNames),
    lists:foreach(
        fun(N) -> 
            spawn(handlers, request_handler, [N, 500, BankNames])
        end,
        lists:seq(1, 5) %=> [1, 2, 3, 4, 5]
     ).

在 shell 中:

~/erlang_programs$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3  (abort with ^G)

1> c(bank).    
bank.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,bank}

2> c(handlers).
handlers.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,handlers}

3> c(my).      
my.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,my}

4> my:go().    
process(<0.84.0>): Format1: 1 500 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 500 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 500 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 500 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 500 [bank1,bank2,bank3] 
ok
process(<0.84.0>): Format2: 1 500 [bank1,bank2,bank3] 
process(<0.85.0>): Format2: 2 500 [bank1,bank2,bank3] 
process(<0.86.0>): Format2: 3 500 [bank1,bank2,bank3] 
process(<0.87.0>): Format2: 4 500 [bank1,bank2,bank3] 
process(<0.88.0>): Format2: 5 500 [bank1,bank2,bank3] 
process(<0.84.0>): Format1: 1 467 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 471 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 465 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 460 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 453 [bank1,bank2,bank3] 
process(<0.84.0>): Format2: 1 467 [bank1,bank2,bank3] 
process(<0.87.0>): Format2: 4 471 [bank1,bank2,bank3] 
process(<0.85.0>): Format2: 2 465 [bank1,bank2,bank3] 
process(<0.86.0>): Format2: 3 460 [bank1,bank2,bank3] 
process(<0.88.0>): Format2: 5 453 [bank1,bank2,bank3] 
process(<0.84.0>): Format1: 1 422 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 441 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 461 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 413 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 442 [bank1,bank2,bank3] 
process(<0.84.0>): Format2: 1 422 [bank1,bank2,bank3] 
process(<0.86.0>): Format2: 3 441 [bank1,bank2,bank3] 
process(<0.87.0>): Format2: 4 461 [bank1,bank2,bank3] 
process(<0.88.0>): Format2: 5 413 [bank1,bank2,bank3] 
process(<0.85.0>): Format2: 2 442 [bank1,bank2,bank3] 
process(<0.84.0>): Format1: 1 405 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 416 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 439 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 376 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 419 [bank1,bank2,bank3] 
process(<0.84.0>): Format2: 1 405 [bank1,bank2,bank3] 
process(<0.86.0>): Format2: 3 416 [bank1,bank2,bank3] 
process(<0.87.0>): Format2: 4 439 [bank1,bank2,bank3] 
process(<0.88.0>): Format2: 5 376 [bank1,bank2,bank3] 
process(<0.85.0>): Format2: 2 419 [bank1,bank2,bank3] 
process(<0.84.0>): Format1: 1 397 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 394 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 389 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 401 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 340 [bank1,bank2,bank3] 
process(<0.84.0>): Format2: 1 397 [bank1,bank2,bank3] 
process(<0.86.0>): Format2: 3 394 [bank1,bank2,bank3] 
process(<0.85.0>): Format2: 2 389 [bank1,bank2,bank3] 
process(<0.87.0>): Format2: 4 401 [bank1,bank2,bank3] 
process(<0.88.0>): Format2: 5 340 [bank1,bank2,bank3] 
process(<0.84.0>): Format1: 1 367 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 400 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 355 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 370 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 313 [bank1,bank2,bank3] 
process(<0.84.0>): Format2: 1 367 [bank1,bank2,bank3] 
process(<0.87.0>): Format2: 4 400 [bank1,bank2,bank3] 
process(<0.86.0>): Format2: 3 355 [bank1,bank2,bank3] 
process(<0.85.0>): Format2: 2 370 [bank1,bank2,bank3] 
process(<0.88.0>): Format2: 5 313 [bank1,bank2,bank3] 
process(<0.84.0>): Format1: 1 337 [bank1,bank2,bank3] 
process(<0.87.0>): Format1: 4 381 [bank1,bank2,bank3] 
process(<0.88.0>): Format1: 5 299 [bank1,bank2,bank3] 
process(<0.86.0>): Format1: 3 329 [bank1,bank2,bank3] 
process(<0.85.0>): Format1: 2 367 [bank1,bank2,bank3] 

^C^C

如您所见，两个 io:format()语句都显示其输出。 ok是 my:go()的返回值，它返回 lists:foreach()返回的所有内容，即 ok。