-module( mutex  ).

-export( [task/0] ).

task() ->
    Mutex = erlang:spawn( fun() -> loop() end ),
    [erlang:spawn(fun() -> random:seed( X, 0, 0 ), print(Mutex, X, 3) end) || X <- lists:seq(1, 3)].



loop() ->
    receive
    {acquire, Pid} ->
        Pid ! {access, erlang:self()},
        receive
        {release, Pid} -> loop()
        end
    end.

mutex_acquire( Pid ) ->
    Pid ! {acquire, erlang:self()},
    receive
    {access, Pid} -> ok
    end.

mutex_release( Pid ) -> Pid ! {release, erlang:self()}.

print( _Mutex, _N, 0 ) -> ok;
print( Mutex, N, M ) ->
    timer:sleep( random:uniform(100) ),
    mutex_acquire( Mutex ),
    io:fwrite( "Print ~p: ", [N] ),
    [print_slow(X) || X <- lists:seq(1, 3)],
    io:nl(),
    mutex_release( Mutex ),
    print( Mutex, N, M - 1 ).

print_slow( X ) ->
    io:fwrite( " ~p", [X] ),
    timer:sleep( 100 ).