zoltans-mutex.erl

%%%-------------------------------------------------------------------
%%% @author tcz
%%% @copyright (C) 2021, <COMPANY>
%%% @doc
%%%
%%% @end
%%% Created : 20. Oct 2021 17:08
%%%-------------------------------------------------------------------
-module(mutex).
-author("tcz").
 
%% API
-export([start/0, init/0, test/0, testinit/0]).
 
start() ->
  register(mutex, spawn(?MODULE, init, [])).
 
stop() ->
  mutex ! stop.
 
init() ->
  process_flag(trap_exit, true),
  free().
 
wait() -> call(wait).
signal() -> call(signal).
 
test() ->
  spawn(?MODULE, testinit, []).
 
testinit() ->
  io:format("Acquiring lock for process ~p...~n", [self()]),
  wait(),
  receive _ -> {} end.
 
call(Message) ->
  mutex ! {Message, self()},
  receive
     {reply, Reply} -> Reply
  end.
reply(Pid, Message) ->
  Pid ! {reply, Message}.
 
free() ->
  receive
    {wait, Pid} ->
      link(Pid),
      reply(Pid, ok),
      busy(Pid)
  end.
 
busy(Pid) ->
  receive
     {signal, Pid} ->
       unlink(Pid),
       reply(Pid, ok),
       free();
     {'EXIT', Pid, Reason} ->
        io:format("Process exited for reason ~p~n", [Reason]),
        unlink(Pid),
        free()
  end.