unexpected messages from wait_for_it when used with Genserver.

[st23am]

link to example to reproduce = https://github.com/cincinnati-elixir/example_genserver_waitforit_bug

Erlang/OTP 20 [erts-9.0] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Interactive Elixir (1.5.0) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> ExampleGenserverWaitforitBug.start_link
{:ok, #PID<0.156.0>}
iex(2)> ExampleGenserverWaitforitBug.hello("world")
"Hello world"
iex(3)>
21:34:33.640 [error] ExampleGenserverWaitforitBug ExampleGenserverWaitforitBug received unexpected message in handle_info/2: {#PID<0.158.0>, 5000}

[jvoegele]

I looked into this and discovered that the reason for the unexpected message was that wait_for_it spawns a waiter process to monitor for timeouts, but it was not properly killing the process when it was done waiting. I had been using Process.exit(waiter, :normal) to kill the waiter process but instead I needed to use Process.exit(waiter, :kill) to forcefully kill the waiter process. I've made this change in master and the next release will include this fix.

Note that if you are using WaitForIt in a GenServer.handle_call callback, your wait timeout must be less than the timeout used when invoking GenServer.call, which by default is 5 seconds. Otherwise, your GenServer.call will timeout before your WaitForIt.wait call times out, leading to the following error:

** (exit) exited in: GenServer.call(ExampleGenserverWaitforitBug, {:request_greeting, "worldz"}, 5000)
** (EXIT) time out