Erlang: spawn_link processes are not killed when everything shuts down normally

Question

Module test:

tester() ->
    receive
        X -> 
            erlang:display("message.."),
            tester()
    end.


initialize() ->
    spawn_link(?MODULE, tester, []),
    erlang:display("Started successfully.").

REPL:

length(erlang:processes()). -> 23
Pid = spawn_link(test, initialize, []).
length(erlang:processes()). -> 24
exit(Pid).
length(erlang:processes()). -> 24

It seems that the spawned tester process is still running! How do i make sure that when i exit my application, all spawn_link process are killed too?

Answer 1

Well, you are actually starting two Erlang processes, not one. The first one, to which you are sending the exit signal, dies before you even send the exit signal, so the exit has no effect.

The first process you start in the shell in this line:

Pid = spawn_link(test, initialize, []).

This process starts executing the initialize function, in which it starts the second process, and then it dies because there is nothing else to do. This is the process to which you are trying to send the exit signal.

To fix this simply return the correct Pid from the initialize function:

initialize() ->
    Pid = spawn_link(?MODULE, tester, []),
    erlang:display("Started successfully."),
    Pid.

And start it directly:

Pid2 = test:initialize().

Then you will be able to kill it with exit(Pid2).