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

Question

I write a code in Erlang and use timer.sleep(), but it is okey and code work when I write timer.sleep(100), but I need more time to stop the thread and when I increase the time and run timer.sleep(100) in function which is called with spawn then the code not working.
In the code the second io does not print in console, so the thread dead in the line time:sleep(1000).
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.
Any body know how I can sleep the thread in erlang for 1000 ms?

Answer 1

In the code the second io does not print in console, so the thread
dead in the line time:sleep(1000).
First off, in erlang we call them processes--not threads. If the process that is running handle_request() dies while it is sleeping, i.e. before the second format statement shows any output, then you should see an error message somewhere.
You haven't provided enough information to help you. Your question is essentially this:
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?
The answer is: because something killed your process.
Here's an example that shows how you can make your request_handler() process sleep for 1 second:
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.
The way the if statement is written above will get rid of the warning:
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).
In the shell:
~/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
Response to comment:
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.
It works for me:
-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]
).
In the shell:
~/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
As you can see, both io:format() statements display their output. The ok is the return value of my:go() which returns whatever lists:foreach() returns, which is ok.