From 70911ba26baae44e6e672d5bde8b84aa2582e874 Mon Sep 17 00:00:00 2001
From: Karl Nilsson <kjnilsson@gmail.com>
Date: Tue, 19 Dec 2023 11:08:48 +0000
Subject: [PATCH] Avoid double notifying on node termiation.

When a node was terminated aten would sometimes send two notifications
to registered listeners. One when it detected the node as not responding
and one next interval when it detected it as gone.

This adds a check for gone case to see if the node has already been
detected as down and only sends a down notification in this scenario
if the prior state is not down.

Also return `ignore` if trying to monitor the current node.
---
 src/aten.erl          | 18 +++++++-----------
 src/aten_detector.erl | 12 ++++++++++--
 src/aten_sink.erl     |  2 --
 3 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/src/aten.erl b/src/aten.erl
index 4dbe3d6..6a4a2c5 100644
--- a/src/aten.erl
+++ b/src/aten.erl
@@ -10,23 +10,19 @@
          start/0,
          register/1,
          unregister/1
-         ]).
-
--export_type([
-              ]).
-
+        ]).
 
 start() ->
     application:ensure_all_started(aten).
 
--spec register(node()) -> ok.
+-spec register(node()) -> ok | ignore.
+register(Node) when Node == node() ->
+    ignore;
 register(Node) ->
     aten_detector:register(Node).
 
--spec unregister(node()) -> ok.
+-spec unregister(node()) -> ok | ignore.
+unregister(Node) when Node == node() ->
+    ignore;
 unregister(Node) ->
     aten_detector:unregister(Node).
-
--ifdef(TEST).
--include_lib("eunit/include/eunit.hrl").
--endif.
diff --git a/src/aten_detector.erl b/src/aten_detector.erl
index 3e2731d..b7fa76f 100644
--- a/src/aten_detector.erl
+++ b/src/aten_detector.erl
@@ -157,10 +157,18 @@ analyse_one(_Curr, _Prev, _Thresh) ->
     no_change.
 
 analyse(Curr, Prev, Thresh) ->
-    Down0 = maps:fold(fun (N, _S, Acc) ->
+    Down0 = maps:fold(fun (N, Sample, Acc) ->
                               case maps:get(N, Curr, undefined) of
                                   undefined ->
-                                      [N | Acc];
+                                      case Sample >= Thresh of
+                                          true ->
+                                              %% already down
+                                              %% this should already have been
+                                              %% been notified
+                                              Acc;
+                                          _ ->
+                                              [N | Acc]
+                                      end;
                                   _ ->
                                       Acc
                               end
diff --git a/src/aten_sink.erl b/src/aten_sink.erl
index 5b0571a..dbcd760 100644
--- a/src/aten_sink.erl
+++ b/src/aten_sink.erl
@@ -8,8 +8,6 @@
 
 -behaviour(gen_server).
 
--include_lib("kernel/include/logger.hrl").
-
 %% API functions
 -export([start_link/0,
          get_failure_probabilities/0,