From 3fe887d79d3cfe5d52c42aa178b912b6521980a2 Mon Sep 17 00:00:00 2001
From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Mon, 24 Aug 2015 20:06:24 -0400
Subject: [PATCH] Track context_switches delta.

---
 include/beam_stats.hrl                    |  1 +
 src/beam_stats.app.src                    |  2 +-
 src/beam_stats_consumer_statsd.erl        | 11 +++++++++++
 src/beam_stats_state.erl                  | 14 ++++++++++++++
 test/beam_stats_consumer_statsd_SUITE.erl |  2 ++
 5 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/include/beam_stats.hrl b/include/beam_stats.hrl
index db26c6d..ae0b48a 100644
--- a/include/beam_stats.hrl
+++ b/include/beam_stats.hrl
@@ -4,6 +4,7 @@
     , memory       :: [{atom(), non_neg_integer()}]
     , io_bytes_in  :: non_neg_integer()
     , io_bytes_out :: non_neg_integer()
+    , context_switches :: non_neg_integer()
     %, statistics   :: [{atom()       , term()}]
     %, system       :: [{atom()       , term()}]
     %, process      :: [{atom()       , term()}]
diff --git a/src/beam_stats.app.src b/src/beam_stats.app.src
index 489c32c..00697fc 100644
--- a/src/beam_stats.app.src
+++ b/src/beam_stats.app.src
@@ -1,7 +1,7 @@
 {application, beam_stats,
  [
   {description, "Periodic VM stats production and consumption."},
-  {vsn, "0.2.0"},
+  {vsn, "0.3.0"},
   {registered, []},
   {applications,
     [ kernel
diff --git a/src/beam_stats_consumer_statsd.erl b/src/beam_stats_consumer_statsd.erl
index c23ead1..5b2f818 100644
--- a/src/beam_stats_consumer_statsd.erl
+++ b/src/beam_stats_consumer_statsd.erl
@@ -144,17 +144,28 @@ beam_stats_to_bins(#beam_stats
     , memory  = Memory
     , io_bytes_in  = IOBytesIn
     , io_bytes_out = IOBytesOut
+    , context_switches = ContextSwitches
     }
 ) ->
     NodeIDBin = node_id_to_bin(NodeID),
     Msgs1 =
         [ io_bytes_in_to_msg(IOBytesIn)
         , io_bytes_out_to_msg(IOBytesOut)
+        , context_switches_to_msg(ContextSwitches)
         | memory_to_msgs(Memory)
         ],
     Msgs2 = [statsd_msg_add_name_prefix(M, NodeIDBin) || M <- Msgs1],
     [statsd_msg_to_bin(M) || M <- Msgs2].
 
+-spec context_switches_to_msg(non_neg_integer()) ->
+    statsd_msg().
+context_switches_to_msg(ContextSwitches) ->
+    #statsd_msg
+    { name  = <<"context_switches">>
+    , value = ContextSwitches
+    , type  = gauge
+    }.
+
 -spec io_bytes_in_to_msg(non_neg_integer()) ->
     statsd_msg().
 io_bytes_in_to_msg(IOBytesIn) ->
diff --git a/src/beam_stats_state.erl b/src/beam_stats_state.erl
index 552b5b1..17f9c90 100644
--- a/src/beam_stats_state.erl
+++ b/src/beam_stats_state.erl
@@ -16,10 +16,14 @@
     { timestamp             :: erlang:timestamp()
     , node_id               :: atom()
     , memory                :: [{atom(), non_neg_integer()}]
+
     , previous_io_bytes_in  :: non_neg_integer()
     , previous_io_bytes_out :: non_neg_integer()
     , current_io_bytes_in   :: non_neg_integer()
     , current_io_bytes_out  :: non_neg_integer()
+
+    , previous_context_switches :: non_neg_integer()
+    ,  current_context_switches :: non_neg_integer()
     }).
 
 -define(T, #?MODULE).
@@ -33,6 +37,7 @@ new() ->
     { {input  , CurrentIOBytesIn}
     , {output , CurrentIOBytesOut}
     } = erlang:statistics(io),
+    {CurrentContextSwitches, 0} = erlang:statistics(context_switches),
     ?T
     { timestamp             = os:timestamp()
     , node_id               = erlang:node()
@@ -41,6 +46,8 @@ new() ->
     , previous_io_bytes_out = 0
     , current_io_bytes_in   = CurrentIOBytesIn
     , current_io_bytes_out  = CurrentIOBytesOut
+    , previous_context_switches = 0
+    ,  current_context_switches = CurrentContextSwitches
     }.
 
 -spec update(t()) ->
@@ -48,11 +55,13 @@ new() ->
 update(?T
     { previous_io_bytes_in  = PreviousIOBytesIn
     , previous_io_bytes_out = PreviousIOBytesOut
+    , previous_context_switches = PreviousContextSwitches
     }
 ) ->
     { {input  , CurrentIOBytesIn}
     , {output , CurrentIOBytesOut}
     } = erlang:statistics(io),
+    {CurrentContextSwitches, 0} = erlang:statistics(context_switches),
     ?T
     { timestamp             = os:timestamp()
     , node_id               = erlang:node()
@@ -61,6 +70,8 @@ update(?T
     , previous_io_bytes_out = PreviousIOBytesOut
     , current_io_bytes_in   = CurrentIOBytesIn
     , current_io_bytes_out  = CurrentIOBytesOut
+    , previous_context_switches = PreviousContextSwitches
+    ,  current_context_switches = CurrentContextSwitches
     }.
 
 -spec export(t()) ->
@@ -74,6 +85,8 @@ export(
     , previous_io_bytes_out = PreviousIOBytesOut
     , current_io_bytes_in   = CurrentIOBytesIn
     , current_io_bytes_out  = CurrentIOBytesOut
+    , previous_context_switches = PreviousContextSwitches
+    ,  current_context_switches = CurrentContextSwitches
     }
 ) ->
     #beam_stats
@@ -82,4 +95,5 @@ export(
     , memory       = Memory
     , io_bytes_in  = CurrentIOBytesIn  - PreviousIOBytesIn
     , io_bytes_out = CurrentIOBytesOut - PreviousIOBytesOut
+    , context_switches = CurrentContextSwitches - PreviousContextSwitches
     }.
diff --git a/test/beam_stats_consumer_statsd_SUITE.erl b/test/beam_stats_consumer_statsd_SUITE.erl
index 161eac1..87f5dd3 100644
--- a/test/beam_stats_consumer_statsd_SUITE.erl
+++ b/test/beam_stats_consumer_statsd_SUITE.erl
@@ -39,6 +39,7 @@ t_send(_Cfg) ->
     , memory    = [{mem_type_foo, 1}]
     , io_bytes_in  = 3
     , io_bytes_out = 7
+    , context_switches = 5
     },
     ServerPort = 8125,
     {ok, ServerSocket} = gen_udp:open(ServerPort, [binary, {active, false}]),
@@ -52,5 +53,6 @@ t_send(_Cfg) ->
     {ok, {_, _, Data}} = ResultOfReceive,
     << "beam_stats.node_foo_host_bar.io.bytes_in:3|g\n"
      , "beam_stats.node_foo_host_bar.io.bytes_out:7|g\n"
+     , "beam_stats.node_foo_host_bar.context_switches:5|g\n"
      , "beam_stats.node_foo_host_bar.memory.mem_type_foo:1|g\n"
     >> = Data.
-- 
2.20.1