Logger.add_backend/1 doesn't outlast Logger.BackendSupervisor #378
Description
Environment
- Elixir version (elixir -v): 1.9.4
- Erlang/OTP version (erl): 22
- Sentry version (mix deps): 7.2.0
- Operating system: any
Description
README advises:
To set this up, add
{:ok, _} = Logger.add_backend(Sentry.LoggerBackend)to your application's start function.
… but Logger.add_backend/2 says:
Backends added by this function are not persisted. Therefore if the Logger application or supervision tree is restarted, the backend won't be available. If you need this guarantee, then configure the backend via the application environment.
Let's try that out:
$ iex -S mix
iex(1)> Logger |> Process.whereis() |> :sys.get_state()
[
{Logger.Backends.Console, false,
%Logger.Backends.Console{
…
iex(2)> Logger.add_backend(Sentry.LoggerBackend)
{:ok, #PID<0.1405.0>}
iex(3)> Logger |> Process.whereis() |> :sys.get_state()
[
{Sentry.LoggerBackend, false,
%Sentry.LoggerBackend{
ignore_plug: true,
include_logger_metadata: false,
level: nil
}},
…
iex(4)> Logger.BackendSupervisor |> Process.whereis() |> Process.exit(:kill)
true
16:45:20.008 [error] GenServer #PID<0.1405.0> terminating
** (stop) killed
Last message: {:EXIT, #PID<0.1169.0>, :killed}
State: {Logger, Sentry.LoggerBackend}
16:45:20.008 [error] GenServer #PID<0.1170.0> terminating
** (stop) killed
Last message: {:EXIT, #PID<0.1169.0>, :killed}
State: {Logger, Logger.Backends.Console}
iex(14)> Logger |> Process.whereis() |> :sys.get_state()
[
{Logger.Backends.Console, false,
%Logger.Backends.Console{
…
Uh oh. The Elixir docs are right: Sentry.LoggerBackend is gone. (The same happens if you call Logger.add_backend/1 from MyApp.start/2 rather than the iex prompt.)
If we apply the docs' advice to configure the backend via the application environment e.g. through config/config.exs…
config :logger,
backends: [:console, Sentry.LoggerBackend]
config :logger, Sentry.LoggerBackend,
# non-default so we can see it made it
include_logger_metadata: true… and check things out again in iex:
$ iex -S mix
iex(1)> Logger |> Process.whereis() |> :sys.get_state()
[
{Sentry.LoggerBackend, false,
%Sentry.LoggerBackend{
ignore_plug: true,
include_logger_metadata: true,
level: nil
}},
…
iex(2)> Logger.BackendSupervisor |> Process.whereis() |> Process.exit(:kill)
true
05:47:53.592 [error] GenServer #PID<0.1170.0> terminating
** (stop) killed
Last message: {:EXIT, #PID<0.1169.0>, :killed}
State: {Logger, Logger.Backends.Console}
function=error_info/7 module=gen_server line=889 file=gen_server.erl pid=<0.1170.0>
05:47:53.592 [error] GenServer #PID<0.1171.0> terminating
** (stop) killed
Last message: {:EXIT, #PID<0.1169.0>, :killed}
State: {Logger, Sentry.LoggerBackend}
function=error_info/7 module=gen_server line=889 file=gen_server.erl pid=<0.1171.0>
iex(3)> Logger |> Process.whereis() |> :sys.get_state()
[
{Sentry.LoggerBackend, false,
%Sentry.LoggerBackend{
ignore_plug: true,
include_logger_metadata: true,
level: nil
}},
…
That'll do!
I also found Logger.BackendSupervisor |> Process.whereis() |> :sys.get_state() helpful while checking this out.
Expected Behavior
Installed as advised, Sentry.LoggerBackend survives a restart of Logger.BackendSupervisor.
Actual Behavior
Installed as advised, Sentry.LoggerBackend does not survive a restart of Logger.BackendSupervisor. I wouldn't worry, much, except we've killed it before and will no doubt kill it again.
Steps to Reproduce
Logger.BackendSupervisor |> Process.whereis() |> Process.exit(:kill)