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April 19, 2017 09:53
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solution to https://www.futurelearn.com/courses/concurrent-programming-erlang/1/assignments/181571/submission/new
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%% Based on code from | |
%% Erlang Programming | |
%% Francecso Cesarini and Simon Thompson | |
%% O'Reilly, 2008 | |
%% http://oreilly.com/catalog/9780596518189/ | |
%% http://www.erlangprogramming.org/ | |
%% (c) Francesco Cesarini and Simon Thompson | |
-module(frequency). | |
-export([start/0,allocate/0,deallocate/1,stop/0]). | |
-export([init/0]). | |
-include_lib("eunit/include/eunit.hrl"). | |
%% These are the start functions used to create and | |
%% initialize the server. | |
start() -> | |
case whereis(frequency) of | |
undefined -> ok; | |
_ -> unregister(frequency) | |
end, | |
register(frequency, | |
spawn(frequency, init, [])). | |
init() -> | |
Frequencies = {get_frequencies(), []}, | |
loop(Frequencies). | |
% Hard Coded | |
get_frequencies() -> [10,11,12,13,14,15]. | |
%% The Main Loop | |
loop(Frequencies) -> | |
timer:sleep(2500), | |
receive | |
{request, Pid, allocate} -> | |
{NewFrequencies, Reply} = allocate(Frequencies, Pid), | |
Pid ! {reply, Reply}, | |
loop(NewFrequencies); | |
{request, Pid , {deallocate, Freq}} -> | |
NewFrequencies = deallocate(Frequencies, Freq), | |
Pid ! {reply, ok}, | |
loop(NewFrequencies); | |
{request, Pid, stop} -> | |
Pid ! {reply, stopped} | |
end. | |
clear() -> | |
receive | |
Msg -> | |
io:format("removing message : ~p~n", [Msg]), | |
clear() | |
after 0 -> | |
ok | |
end. | |
%% Functional interface | |
allocate() -> | |
clear(), | |
frequency ! {request, self(), allocate}, | |
receive | |
{reply, Reply} -> Reply | |
after 2000 -> | |
{error, server_overload} | |
end. | |
deallocate(Freq) -> | |
clear(), | |
frequency ! {request, self(), {deallocate, Freq}}, | |
receive | |
{reply, Reply} -> Reply | |
after 2000 -> | |
{error, server_overload} | |
end. | |
stop() -> | |
clear(), | |
frequency ! {request, self(), stop}, | |
receive | |
{reply, Reply} -> Reply | |
after 2000 -> | |
{error, server_overload} | |
end. | |
%% The Internal Help Functions used to allocate and | |
%% deallocate frequencies. | |
allocate({[], Allocated}, _Pid) -> | |
{{[], Allocated}, {error, no_frequency}}; | |
allocate({[Freq|Free], Allocated}, Pid) -> | |
{{Free, [{Freq, Pid}|Allocated]}, {ok, Freq}}. | |
deallocate({Free, Allocated}, Freq) -> | |
NewAllocated=lists:keydelete(Freq, 1, Allocated), | |
{[Freq|Free], NewAllocated}. |
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