From 879fea84045d606716454fbaaecd39f84be69782 Mon Sep 17 00:00:00 2001
From: Matthias Radestock <matthias@lshift.net>
Date: Fri, 18 Sep 2009 06:08:44 +0100
Subject: handle timeouts in cpu_sup:avg1 gracefully Also, it turns out that
 the load avg is an int, not a float

---
 src/rabbit_load.erl | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/rabbit_load.erl b/src/rabbit_load.erl
index 7bf85347..6ef638cb 100644
--- a/src/rabbit_load.erl
+++ b/src/rabbit_load.erl
@@ -41,7 +41,7 @@
 -ifdef(use_specs).
 
 -type(erlang_node() :: atom()).
--type(load() :: {{non_neg_integer(), float()}, erlang_node()}).
+-type(load() :: {{non_neg_integer(), integer() | 'unknown'}, erlang_node()}).
 -spec(local_load/0 :: () -> load()).
 -spec(remote_loads/0 :: () -> [load()]).
 -spec(pick/0 :: () -> erlang_node()).
@@ -52,8 +52,11 @@
 
 local_load() ->
     LoadAvg = case whereis(cpu_sup) of
-                  undefined -> 0.0;
-                  _Other -> cpu_sup:avg1()
+                  undefined -> unknown;
+                  _         -> case cpu_sup:avg1() of
+                                   L when is_integer(L) -> L;
+                                   {error, timeout}     -> unknown
+                               end
               end,
     {{statistics(run_queue), LoadAvg}, node()}.
 
@@ -65,8 +68,12 @@ remote_loads() ->
 pick() ->
     RemoteLoads = remote_loads(),
     {{RunQ, LoadAvg}, Node} = local_load(),
-    %% add bias towards current node
-    AdjustedLoadAvg = LoadAvg * ?FUDGE_FACTOR,
+    %% add bias towards current node; we rely on Erlang's term order
+    %% of SomeFloat < local_unknown < unknown.
+    AdjustedLoadAvg = case LoadAvg of
+                          unknown -> local_unknown;
+                          _       -> LoadAvg * ?FUDGE_FACTOR
+                      end,
     Loads = [{{RunQ, AdjustedLoadAvg}, Node} | RemoteLoads],
     {_, SelectedNode} = lists:min(Loads),
     SelectedNode.
-- 
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