DEBUG-3457 hack probe notifier worker starting

Author: p

lib/datadog/di/component.rb

@@ -84,7 +84,18 @@ def initialize(settings, agent_settings, logger, code_tracker: nil, telemetry: n
         @probe_notifier_worker = ProbeNotifierWorker.new(settings, transport, logger, telemetry: telemetry)
         @probe_notification_builder = ProbeNotificationBuilder.new(settings, serializer)
         @probe_manager = ProbeManager.new(settings, instrumenter, probe_notification_builder, probe_notifier_worker, logger, telemetry: telemetry)
-        probe_notifier_worker.start
+
+        # If the worker is started here, it will be in the parent process
+        # of forking web servers like puma rather than in the worker processes
+        # that actually process HTTP requests, and thus DI will end up not
+        # sending any events to the agent.
+        #
+        # There is currently no "nice" way to handle this situation correctly -
+        # remote config has the same issue and the tracing Rack middleware
+        # presently starts the remote config worker.
+        #
+        # DI is hacked into that middleware the same way.
+        #probe_notifier_worker.start
       end
 
       attr_reader :settings

lib/datadog/tracing/contrib/rack/middlewares.rb

@@ -39,6 +39,10 @@ def call(env)
 
             boot = Datadog::Core::Remote::Tie.boot
 
+            if defined?(Datadog::DI)
+              Datadog::DI.current_component&.probe_notifier_worker&.start
+            end
+
             # Extract distributed tracing context before creating any spans,
             # so that all spans will be added to the distributed trace.
             if configuration[:distributed_tracing]

spec/datadog/di/integration/everything_from_remote_config_spec.rb

@@ -106,6 +106,9 @@ def target_method
 
   before do
     expect(Datadog::DI).to receive(:component).at_least(:once).and_return(component)
+
+    # This is done by tracing Rack middleware in actual applications
+    component.probe_notifier_worker.start
   end
 
   let(:mock_response) do

spec/datadog/di/integration/instrumentation_spec.rb

@@ -107,6 +107,9 @@ def mutating_method(greeting)
       allow(agent_settings).to receive(:ssl)
 
       allow(Datadog::DI).to receive(:current_component).and_return(component)
+
+      # This is done by tracing Rack middleware in actual applications
+      component.probe_notifier_worker.start
     end
 
     context 'method probe' do