erlang semaphore (mutex) - erlang

Question

i found example of mutex in erlang
Can somebody modify it to use it with count like semaphore?
-module(mutex).
-export([start/0, stop/0]).
-export([wait/0, signal/0]).
-export([init/0]).
start() ->
register(mutex, spawn(?MODULE, init, [])).
stop() ->
mutex ! stop.
wait() ->
mutex ! {wait, self()},
receive ok -> ok end.
signal() ->
mutex ! {signal, self()},
ok.
init() ->
free().
free() ->
receive
{wait, Pid} ->
Pid ! ok,
busy(Pid);
stop ->
terminate()
end.
busy(Pid) ->
receive
{signal, Pid} ->
free()
end.
terminate() ->
receive
{wait, Pid} ->
exit(Pid, kill),
terminate()
after
0 -> ok
end.

Answer 1

Thats not the best semaphore.. could use some random stuff, but hopefully you will get the idea.
-module(sem1).
-export([semaphor/2, start/1, start/0]).
semaphor(0,0) ->
io:format("err");
semaphor(0,Full)->
receive
{increment,PID} ->
io:format("UP ~w ~w~n", [0,PID]),
PID ! {incGranted},
semaphor(1,Full)
end;
semaphor(Full,Full)->
receive
{decrement,PID} ->
io:format("DOWN ~w ~w~n", [Full,PID]),
PID ! {decGranted},
semaphor(Full -1 , Full)
end;
semaphor(N,Full)->
receive
{decrement,PID} ->
io:format("DOWN ~w ~w~n", [N,PID]),
PID ! {decGranted},
semaphor(N -1 , Full);
{increment,PID} ->
io:format("UP ~w ~w~n", [N,PID]),
PID ! {incGranted},
semaphor(N + 1 , Full)
end.
start(PID) ->
PID ! {decrement, self()},
receive
{decGranted} -> true
end,
timer:sleep(100),
PID ! {increment, self()},
receive
{incGranted} -> true
end,
start(PID).
start() ->
PID = spawn(sem1, semafor, [1,5]),
spawn(sem1,start,[PID]),
spawn(sem1,start,[PID]),
spawn(sem1,start,[PID]),
spawn(sem1,start,[PID]),
spawn(sem1,start,[PID]),
spawn(sem1,start,[PID]).