Processus
Un meilleur verrou

-module (block).
-export ([lock/1, guard/2]).

guard (Owner, N) ->
    receive
        {lock, From} when N == 0 ->
            From ! ok,
            guard (From, 1);
        {lock, Owner} ->
            Owner ! ok,
            guard (Owner, N+1);
        {unlock, Owner} when N > 1 ->
            guard (Owner, N-1);
        {unlock, Owner} when N == 1 ->
            unlink (Owner),
            guard (none, 0);
        {'EXIT', Owner, _} when N > 0 ->
            guard (none, 0)
    end.

lock (Lock) ->
    link (Lock),
    Lock ! {lock, self()},
    receive
        ok -> ok
    end.
            
unlock (Lock) ->
    Lock ! {unlock, self()}.