[erlang-questions] Exit signals are funny things

Alex S. alex0player@REDACTED
Fri May 5 14:08:15 CEST 2017

There is exit/1 and exit/2 which are very, very different things. exit/1 is NOT an exit signal.
There is no “kill and kill”, there is exit signal kill, which is special, and exit reason kill, which is not special.
> 5 мая 2017 г., в 15:05, Robert Virding <rvirding@REDACTED> написал(а):
> There is more. So:
> 1> process_flag(trap_exit, true).
> false
> 2> Pid = spawn_link(fun() -> process_flag(trap_exit,true), timer:sleep(infinity) end).
> <0.60.0>
> We trap exits and spawn_link which also traps exits and just hangs there waiting.
> 3> spawn(fun() -> link(Pid), exit(kill) end).
> <0.62.0>
> 4> process_info(Pid, messages).
> {messages,[{'EXIT',<0.62.0>,kill}]}
> Now we spawn a new process which links to our hanger and exits with the reason 'kill'. We can then check our hanger and see that it received a 'kill' signal which it converted to a message because it was trapping. Finally:
> 5> spawn(fun() -> exit(Pid, kill) end).
> <0.65.0>
> 6> flush().
> Shell got {'EXIT',<0.60.0>,killed}
> ok
> we spawn another process which uses exit/2 to send a 'kill' signal to our hanger and in this case it cannot trap the signal and dies with the reason 'killed'. So there is 'kill' and 'kill' depending on how I send it.
> Where's the logic in that?
> Robert
> P.S. Yes, I know that getting a 'killed' from a process which has been killed with a 'kill' signal is the correct.
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