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June 30, 2020 18:48
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Concurrent Programming in Erlang - The University of Kent - chapter 2.5
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-module(frequency_updated). | |
-export([loop/1, init/1, stop/0, allocate_freq/0, deallocate_freq/1, demo/0, use_freq/0]). | |
-define(TIMEOUT, 5000). | |
%% server implementation | |
allocate({[], Allocated}, _Pid) -> | |
{{[], Allocated}, {error, no_frequency}}; | |
allocate({[Freq | Free], Allocated}, Pid) -> | |
case lists:keymember(Pid, 2, Allocated) of | |
true -> {{[Freq | Free], Allocated}, {error, already_allocated}}; | |
false -> {{Free, [{Freq, Pid} | Allocated]}, {ok, Freq}} | |
end. | |
deallocate({Free, Allocated}, {Freq, Pid}) -> | |
case lists:keyfind(Freq, 1, Allocated) of | |
{Freq, Pid} -> | |
NewAllocated = lists:delete({Freq, Pid}, Allocated), | |
{{[Freq | Free], NewAllocated}, ok}; | |
{Freq, _} -> | |
{{Free, Allocated}, unauthorized}; | |
false -> | |
{{Free, Allocated}, not_allocated} | |
end. | |
loop(Frequencies) -> | |
receive | |
{request, Pid, allocate} -> | |
{NewFrequencies, Reply} = allocate(Frequencies, Pid), | |
Pid ! {reply, Reply}, | |
loop(NewFrequencies); | |
{request, Pid, {deallocate, Freq}} -> | |
{NewFrequencies, Reply} = deallocate(Frequencies, {Freq, Pid}), | |
Pid ! {reply, Reply}, | |
loop(NewFrequencies); | |
{request, Pid, stop} -> | |
Pid ! {reply, stopped} | |
end. | |
%% private functions | |
clear() -> | |
receive | |
_Msg -> clear() | |
after 0 -> | |
ok | |
end. | |
wait_reply() -> | |
receive | |
{reply, Rep} -> Rep | |
after ?TIMEOUT -> | |
clear(), | |
{error, timout} | |
end. | |
%% API | |
init(Frequencies) -> | |
Server = spawn(frequency_updated, loop, [{Frequencies, []}]), | |
register(frequency_updated, Server). | |
stop() -> | |
frequency_updated ! {request, self(), stop}, | |
wait_reply(). | |
allocate_freq() -> | |
frequency_updated ! {request, self(), allocate}, | |
wait_reply(). | |
deallocate_freq(Frequency) -> | |
frequency_updated ! {request, self(), {deallocate, Frequency}}, | |
wait_reply(). | |
%% demo | |
use_freq() -> | |
{ok, Freq} = allocate_freq(), | |
io:format("allocated frequency ~w, releasing in 2 seconds~n", [Freq]), | |
timer:sleep(2000), | |
deallocate_freq(Freq), | |
io:format("released frequency ~w~n", [Freq]). | |
spawn_client() -> | |
spawn(frequency_updated, use_freq, []). | |
demo() -> | |
init([10, 11, 12]), | |
spawn_client(), | |
spawn_client(), | |
timer:sleep(3000), | |
stop(), | |
ok. |
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Nicely done!