# Programming Elixir - A Fibonacci Server

Hi, somehow, after typing code from book i managed only to make my code stuck at infinite loop. I did comparision side by side of my code to that i get from zipped examples i got with book (code from zip works ok). I can’t find where did i do mistake. Can anyone spot what did do wrong? I know i can move on, i understand what is going on, but it’s driving me nuts, beside, there is a big chance i won’t repeat that mistake if only i would know where it is

Anyway, here’s the code:

``````defmodule FibSolver do

def fib(scheduler) do
{ :fib, n, client } ->
send(client, { :answer, n, fib_calc(n), self })
fib(scheduler)
{ :shutdown } ->
exit(:normal)
end
end

defp fib_calc(0), do: 0
defp fib_calc(1), do: 1
defp fib_calc(n), do: fib_calc(n-1) + fib_calc(n-2)
end

defmodule Scheduler do

def run(num_processes, module, func, to_calculate) do
(1..num_processes)
|> Enum.map(fn(_) -> spawn(module, func, [self]) end)
|> schedule_processes(to_calculate, [])
end

defp schedule_processes(processes, queue, results) do
{ :ready, pid } when length(queue) > 0 ->
[ next | tail ] = queue
send(pid, { :fib, next, self })
schedule_processes(processes, tail, results)
send(pid, { :shutdown })
if length(processes) > 1 do
schedule_processes(List.delete(processes, pid), queue, results)
else
Enum.sort(results, fn {n1,_}, {n2,_} -> n1 <= n2 end)
end
{ :answer, number, result, _pid } ->
schedule_processes(processes, queue, [{ number, result } | results])
end
end
end

to_process = [37, 37, 37, 37, 37, 37]

Enum.each(1..10, fn num_processes ->
{ time, result } = :timer.tc(Scheduler, :run, [num_processes, FibSolver, :fib, to_process])
if num_processes == 1 do
IO.puts(inspect(result))
IO.puts("\n #  time(s)")
end
:io.format("~2B     ~.2f~n", [num_processes, time/1000000.0])
end)
``````
3 Likes

Looks like that should be `{:ready, self}`. Can’t start the circus if it’s never telling the Scheduler it’s ready.

5 Likes

Thank you very much. Such typos are hard to spot, i normally rely on IDE to help me with them, but i have none for elixir

I think the lesson for me is to also pattern match “anything” at end of receive and exit program printing the oddity I just catch, at least when I’m learning

PS. Func fact: Single core performance of my 1.6 Ghz i5 in mac book air (OSX) is better than single core performance of 3.7 Ghz AMD (Win10)

3 Likes

Deciding what to do when you get a message in which you are not interested is a general problem. Should I crash, or should I ignore it, or what? Unfortunately there is no general solution which is good for everyone everywhere.

Just some philosophy.

Robert

3 Likes

This is very true.

For completeness: When you use an OTP GenServer, it picks the ‘let it crash’ approach for you, as it will simply attempt to call a variant of `handle_call`, `handle_cast` or `handle_info` that does not exist. (Of course, when you don’t have, for instance, any overridden variants of `handle_info`, it will default to doing nothing with any info-messages it receives).

You can of course change it to the second variant by creating a fallback function variant that accepts any other message.

2 Likes