Fix a thread safety issue with the agent.

Make sure we pass the metric when we create a pipeline this make sure
the metric is correctly visible in the pipeline and remove the need to
lock the variables.

Make the expectation more robust in the metric reload scenario.

Fixes #5400 for the greater good.

Fixes #5446

logstash-core/lib/logstash/agent.rb

@@ -45,8 +45,10 @@ class LogStash::Agent
     @upgrade_mutex = Mutex.new
 
     @collect_metric = setting("metric.collect")
-    @metric = create_metric_collector
-    @periodic_pollers = LogStash::Instrument::PeriodicPollers.new(create_metric_collector)
+
+
+    # Create the collectors and configured it with the library
+    configure_metrics_collectors
   end
 
   def execute
@@ -156,14 +158,25 @@ class LogStash::Agent
     end
   end
 
-  def create_metric_collector
-    if collect_metrics?
+  def configure_metrics_collectors
+    @collector = LogStash::Instrument::Collector.new
+
+    @metric = if collect_metrics?
                 @logger.debug("Agent: Configuring metric collection")
-      LogStash::Instrument::Collector.instance.agent = self
-      LogStash::Instrument::Metric.new
+                LogStash::Instrument::Metric.new(@collector)
               else
                 LogStash::Instrument::NullMetric.new
               end
+
+
+    @periodic_pollers = LogStash::Instrument::PeriodicPollers.new(@metric)
+  end
+
+  def reset_metrics_collectors
+    @periodic_pollers.stop
+    @collector.stop
+    configure_metrics_collectors
+    @periodic_pollers.start
   end
 
   def collect_metrics?
@@ -171,7 +184,6 @@ class LogStash::Agent
   end
 
   def create_pipeline(settings, config=nil)
-
     if config.nil?
       begin
         config = fetch_config(settings)
@@ -182,7 +194,7 @@ class LogStash::Agent
     end
 
     begin
-      LogStash::Pipeline.new(config, settings)
+      LogStash::Pipeline.new(config, settings, metric)
     rescue => e
       @logger.error("fetched an invalid config", :config => config, :reason => e.message)
       return
@@ -204,6 +216,11 @@ class LogStash::Agent
       return
     end
 
+    # Reset the current collected stats,
+    # starting a pipeline with a new configuration should be the same as restarting
+    # logstash.
+    reset_metrics_collectors
+
     new_pipeline = create_pipeline(old_pipeline.settings, new_config)
 
     return if new_pipeline.nil?
@@ -225,12 +242,6 @@ class LogStash::Agent
     return unless pipeline.is_a?(LogStash::Pipeline)
     return if pipeline.ready?
     @logger.info("starting pipeline", :id => id)
-
-    # Reset the current collected stats,
-    # starting a pipeline with a new configuration should be the same as restarting
-    # logstash.
-    reset_collector
-
     Thread.new do
       LogStash::Util.set_thread_name("pipeline.#{id}")
       begin
@@ -266,6 +277,8 @@ class LogStash::Agent
   def upgrade_pipeline(pipeline_id, new_pipeline)
     stop_pipeline(pipeline_id)
     @pipelines[pipeline_id] = new_pipeline
+
+    new_pipeline = metric
     start_pipeline(pipeline_id)
   end
 
@@ -273,10 +286,6 @@ class LogStash::Agent
     @pipelines.empty?
   end
 
-  def reset_collector
-    LogStash::Instrument::Collector.instance.clear
-  end
-
   def setting(key)
     @settings.get(key)
   end

logstash-core/lib/logstash/instrument/collector.rb

@@ -8,7 +8,7 @@ require "singleton"
 require "thread"
 
 module LogStash module Instrument
-  # The Collector singleton is the single point of reference for all
+  # The Collector is the single point of reference for all
   # the metrics collection inside logstash, the metrics library will make
   # direct calls to this class.
   #
@@ -91,6 +91,10 @@ module LogStash module Instrument
       @snapshot_task.execute
     end
 
+    def stop
+      @snapshot_task.shutdown
+    end
+
     # Create a snapshot of the MetricStore and send it to to the registered observers
     # The observer will receive the following signature in the update methode.
     #

logstash-core/lib/logstash/pipeline.rb

@@ -32,8 +32,8 @@ module LogStash; class Pipeline
     :started_at,
     :thread,
     :config_str,
-    :settings
-  attr_accessor :metric
+    :settings,
+    :metric
 
   MAX_INFLIGHT_WARN_THRESHOLD = 10_000
 
@@ -41,7 +41,7 @@ module LogStash; class Pipeline
     "LogStash::Inputs::Stdin"
   ]
 
-  def initialize(config_str, settings = LogStash::SETTINGS)
+  def initialize(config_str, settings = LogStash::SETTINGS, provided_metric = nil)
     @config_str = config_str
     @logger = Cabin::Channel.get(LogStash)
     @settings = settings
@@ -56,7 +56,7 @@ module LogStash; class Pipeline
 
     # This needs to be configured before we evaluate the code to make
     # sure the metric instance is correctly send to the plugins to make the namespace scoping work
-    @metric = settings.get_value("metric.collect") ? Instrument::Metric.new : Instrument::NullMetric.new 
+    @metric = provided_metric.nil? ? LogStash::Instrument::NullMetric.new : provided_metric
 
     grammar = LogStashConfigParser.new
     @config = grammar.parse(config_str)

logstash-core/spec/logstash/agent_spec.rb

@@ -328,11 +328,11 @@ describe LogStash::Agent do
     end
   end
 
+
   context "metrics after config reloading" do
-    let(:dummy_output) { DummyOutput.new }
     let(:config) { "input { generator { } } output { dummyoutput { } }" }
-    let(:new_config_generator_counter) { 50 }
-    let(:new_config) { "input { generator { count => #{new_config_generator_counter} } } output { dummyoutput {} }" }
+    let(:new_config_generator_counter) { 500 }
+    let(:new_config) { "input { generator { count => #{new_config_generator_counter} } } output { dummyoutput2 {} }" }
     let(:config_path) do
       f = Stud::Temporary.file
       f.write(config)
@@ -353,11 +353,24 @@ describe LogStash::Agent do
                     "metric.collect" => true })
     end 
 
+    # We need to create theses dummy classes to know how many
+    # events where actually generated by the pipeline and successfully send to the output.
+    # Theses values are compared with what we store in the metric store.
+    let!(:dummy_output) { DummyOutput.new }
+    let!(:dummy_output2) { DummyOutput.new }
+    class DummyOutput2 < LogStash::Outputs::Base; end
+
     before :each do
       allow(DummyOutput).to receive(:new).at_least(:once).with(anything).and_return(dummy_output)
+      allow(DummyOutput2).to receive(:new).at_least(:once).with(anything).and_return(dummy_output2)
+
       allow(LogStash::Plugin).to receive(:lookup).with("input", "generator").and_return(LogStash::Inputs::Generator)
       allow(LogStash::Plugin).to receive(:lookup).with("codec", "plain").and_return(LogStash::Codecs::Plain)
       allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput").and_return(DummyOutput)
+      allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput2").and_return(DummyOutput2)
+
+      @abort_on_exception = Thread.abort_on_exception
+      Thread.abort_on_exception = true
 
       @t = Thread.new do
         subject.register_pipeline("main",  pipeline_settings)
@@ -371,25 +384,32 @@ describe LogStash::Agent do
       subject.shutdown
       Stud.stop!(@t)
       @t.join
+      Thread.abort_on_exception = @abort_on_exception
     end
 
     it "resets the metric collector" do
       # We know that the store has more events coming in.
-      sleep(0.01) while dummy_output.events.size < new_config_generator_counter
-      snapshot = LogStash::Instrument::Collector.instance.snapshot_metric
+      while dummy_output.events.size <= new_config_generator_counter
+        sleep(0.1)
+      end
+
+      snapshot = subject.metric.collector.snapshot_metric
       expect(snapshot.metric_store.get_with_path("/stats/events")[:stats][:events][:in].value).to be > new_config_generator_counter
 
       # update the configuration and give some time to logstash to pick it up and do the work
-      IO.write(config_path, new_config)
+      # Also force a flush to disk to make sure ruby reload it.
+      File.open(config_path, "w") do |f|
+        f.write(new_config)
+        f.fsync
+      end
 
       sleep(interval * 3) # Give time to reload the config
       
-      # Since there is multiple threads involved with the configuration reload, 
-      # It can take some time to the stats be visible in the store but it will
       # be eventually consistent.
-      sleep(0.01) while dummy_output.events.size < new_config_generator_counter
+      sleep(0.01) while dummy_output2.events.size < new_config_generator_counter
 
-      value = LogStash::Instrument::Collector.instance.snapshot_metric.metric_store.get_with_path("/stats/events")[:stats][:events][:in].value
+      snapshot = subject.metric.collector.snapshot_metric
+      value = snapshot.metric_store.get_with_path("/stats/events")[:stats][:events][:in].value
       expect(value).to eq(new_config_generator_counter)
     end
   end

logstash-core/spec/logstash/pipeline_spec.rb

@@ -554,10 +554,12 @@ describe LogStash::Pipeline do
   end
 
   context "when collecting metrics in the pipeline" do
+    let(:metric) { LogStash::Instrument::Metric.new(LogStash::Instrument::Collector.new) }
+
+    subject { described_class.new(config, pipeline_settings_obj, metric) }
+
     let(:pipeline_settings) { { "pipeline.id" => pipeline_id } }
-    subject { described_class.new(config, pipeline_settings_obj) }
     let(:pipeline_id) { "main" }
-    let(:metric) { LogStash::Instrument::Metric.new }
     let(:number_of_events) { 1000 }
     let(:multiline_id) { "my-multiline" }
     let(:multiline_id_other) { "my-multiline_other" }
@@ -591,6 +593,7 @@ describe LogStash::Pipeline do
       EOS
     end
     let(:dummyoutput) { DummyOutput.new({ "id" => dummy_output_id }) }
+    let(:metric_store) { subject.metric.collector.snapshot_metric.metric_store }
 
     before :each do
       allow(DummyOutput).to receive(:new).with(any_args).and_return(dummyoutput)
@@ -599,9 +602,6 @@ describe LogStash::Pipeline do
       allow(LogStash::Plugin).to receive(:lookup).with("filter", "multiline").and_return(LogStash::Filters::Multiline)
       allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput").and_return(DummyOutput)
 
-      # Reset the metric store
-      LogStash::Instrument::Collector.instance.clear
-
       Thread.new { subject.run }
       # make sure we have received all the generated events
       sleep 1 while dummyoutput.events.size < number_of_events
@@ -612,7 +612,7 @@ describe LogStash::Pipeline do
     end
 
     context "global metric" do
-      let(:collected_metric) { LogStash::Instrument::Collector.instance.snapshot_metric.metric_store.get_with_path("stats/events") }
+      let(:collected_metric) { metric_store.get_with_path("stats/events") }
 
       it "populates the differents" do
         expect(collected_metric[:stats][:events][:in].value).to eq(number_of_events)
@@ -622,7 +622,7 @@ describe LogStash::Pipeline do
     end
 
     context "pipelines" do
-      let(:collected_metric) { LogStash::Instrument::Collector.instance.snapshot_metric.metric_store.get_with_path("stats/pipelines/") }
+      let(:collected_metric) { metric_store.get_with_path("stats/pipelines/") }
 
       it "populates the pipelines core metrics" do
         expect(collected_metric[:stats][:pipelines][:main][:events][:in].value).to eq(number_of_events)

logstash-core/spec/support/mocks_classes.rb

@@ -1,5 +1,6 @@
 # encoding: utf-8
 require "logstash/outputs/base"
+require "thread"
 
 class DummyOutput < LogStash::Outputs::Base
   config_name "dummyoutput"
@@ -10,7 +11,7 @@ class DummyOutput < LogStash::Outputs::Base
   def initialize(params={})
     super
     @num_closes = 0
-    @events = []
+    @events = Queue.new
   end
 
   def register