exit/1, exit/2, link, trap_exit

trap.erl

-module(trap).
-export([simple_exit_demo/0, kill_demo_v2/0, kill_demo/0, successfully_killing_a_non_system_process/0]).


listen() ->
  receive
    Message -> io:format("~p has caught a system message: ~p~n~n", [self(), Message]),
    listen()
  after 1000 ->
    io:format("I, ~p, live on~n", [self()]),
    listen()
  end.


kill_demo() ->
  Pid = spawn_link(fun()->
      process_flag(trap_exit, true),
      listen()
  end),

  % this will fail, the recipient process traps all exit signals
  timer:sleep(3000),
  io:format("Sending exit(Pid, please_die) ~p to ~n", [Pid]),  
  exit(Pid, please_die),

  % "The kill reason acts as a special signal that can't be trapped."
  timer:sleep(4000),
  io:format("Sending exit(Pid, kill) ~p to ~n", [Pid]),
  exit(Pid, kill).

%%%%%%%

kill_demo_v2() ->
  Pid = spawn_link(fun()->
      process_flag(trap_exit, true),
      listen()
  end),

  process_flag(trap_exit, true),
  % this will fail, the recipient process traps all exit signals
  timer:sleep(3000),
  io:format("Sending exit(Pid, please_die) ~p to ~n", [Pid]),  
  exit(Pid, please_die),

  % "The kill reason acts as a special signal that can't be trapped."
  timer:sleep(4000),
  io:format("Sending exit(Pid, kill) ~p to ~n", [Pid]),
  exit(Pid, kill),
  receive
    Message -> io:format("~p has caught a system message: ~p~n~n", [self(), Message])
  end.


%%%%%%%


% seems like in order to send exit() from A to B  they needn't be linked (spawn instead of spawn_link)
successfully_killing_a_non_system_process() ->
  Victim = spawn(fun()->
    io:format("Victim process alive (~p)~n", [self()]),
    receive
      Res -> Res
    after 2000 -> 
      % this will never happen, the process will be killed before
      io:format("Dying my own natural death (~p)~n", [self()])
    end
  end),

  % this will fail, the recipient process traps all exit signals
  timer:sleep(1000),
  io:format("Sending exit(Victim, please_die)  to ~p ~n", [Victim]),  
  exit(Victim, please_die).
  
  
%%%%%%%%

simple_exit_demo() ->
  spawn(fun() -> start_processes() end).

start_processes() ->
  process_flag(trap_exit, true),
  spawn_link(fun() -> timer:sleep(1000) end),
  spawn_link(fun() -> timer:sleep(2000), exit(exiting_for_a_reason) end),
  spawn_link(fun() -> timer:sleep(3000), exit(normal) end),
  spawn_link(fun() -> timer:sleep(4000), 1 / 0 end),
  spawn_link(fun() -> timer:sleep(5000), erlang:error(raising_error) end),
  spawn_link(fun() -> timer:sleep(6000), throw(throwing_error) end),
  listen_to_exits().

listen_to_exits() ->
  receive
    Message -> io:format("Caught a system message: ~p~n~n", [Message]),
               listen_to_exits()
  after 7000 ->
    io:format("Show's over~n")
  end.