perf: Reduce Context Allocations in ActiveJob (#1018)

* perf: Reduce Context Allocations in ActiveJob

After seeing changes to Rack::Events that reduced the number of active contexts required for ingress spans,
I decided to apply the same changes to ActiveJob

* doc: Update default.rb

Co-authored-by: Steven Harman <[email protected]>

---------

Co-authored-by: Steven Harman <[email protected]>

instrumentation/active_job/Appraisals

@@ -9,3 +9,7 @@
     gem 'activejob', "~> #{version}"
   end
 end
+
+appraise 'activejob-latest' do
+  gem 'activejob'
+end

instrumentation/active_job/lib/opentelemetry/instrumentation/active_job/handlers/default.rb

@@ -41,9 +41,9 @@ def start(name, id, payload)
           # @return [Hash] with the span and generated context tokens
           def start_span(name, _id, payload)
             span = tracer.start_span(name, attributes: @mapper.call(payload))
-            tokens = [OpenTelemetry::Context.attach(OpenTelemetry::Trace.context_with_span(span))]
+            token = OpenTelemetry::Context.attach(OpenTelemetry::Trace.context_with_span(span))
 
-            { span: span, ctx_tokens: tokens }
+            { span: span, ctx_token: token }
           end
 
           # Creates a span and registers it with the current context
@@ -55,20 +55,20 @@ def start_span(name, _id, payload)
           def finish(_name, _id, payload)
             otel = payload.delete(:__otel)
             span = otel&.fetch(:span)
-            tokens = otel&.fetch(:ctx_tokens)
+            token = otel&.fetch(:ctx_token)
 
             on_exception((payload[:error] || payload[:exception_object]), span)
           rescue StandardError => e
             OpenTelemetry.handle_error(exception: e)
           ensure
-            finish_span(span, tokens)
+            finish_span(span, token)
           end
 
           # Finishes the provided spans and also detaches the associated contexts
           #
           # @param span [OpenTelemetry::Trace::Span]
-          # @param tokens [Array] to unregister
-          def finish_span(span, tokens)
+          # @param token [Numeric] to unregister
+          def finish_span(span, token)
             # closes the span after all attributes have been finalized
             begin
               if span&.recording?
@@ -79,8 +79,7 @@ def finish_span(span, tokens)
               OpenTelemetry.handle_error(exception: e)
             end
 
-            # pops the context stack
-            tokens&.reverse_each do |token|
+            begin
               OpenTelemetry::Context.detach(token)
             rescue StandardError => e
               OpenTelemetry.handle_error(exception: e)

instrumentation/active_job/lib/opentelemetry/instrumentation/active_job/handlers/enqueue.rb

@@ -29,9 +29,8 @@ def initialize(...)
           def start_span(name, _id, payload)
             job = payload.fetch(:job)
             span = tracer.start_span(@span_name_formatter.call(job), kind: :producer, attributes: @mapper.call(payload))
-            tokens = [OpenTelemetry::Context.attach(OpenTelemetry::Trace.context_with_span(span))]
             OpenTelemetry.propagation.inject(job.__otel_headers) # This must be transmitted over the wire
-            { span: span, ctx_tokens: tokens }
+            { span: span, ctx_token: OpenTelemetry::Context.attach(OpenTelemetry::Trace.context_with_span(span)) }
           end
         end
       end

instrumentation/active_job/lib/opentelemetry/instrumentation/active_job/handlers/perform.rb

@@ -27,7 +27,6 @@ def initialize(...)
           # @param payload [Hash] containing job run information
           # @return [Hash] with the span and generated context tokens
           def start_span(name, _id, payload)
-            tokens = []
             job = payload.fetch(:job)
             parent_context = OpenTelemetry.propagation.extract(job.__otel_headers)
 
@@ -36,30 +35,27 @@ def start_span(name, _id, payload)
             # TODO: Refactor into a propagation strategy
             propagation_style = @config[:propagation_style]
             if propagation_style == :child
-              tokens << OpenTelemetry::Context.attach(parent_context)
               span = tracer.start_span(span_name, kind: :consumer, attributes: @mapper.call(payload))
             else
               span_context = OpenTelemetry::Trace.current_span(parent_context).context
               links = [OpenTelemetry::Trace::Link.new(span_context)] if span_context.valid? && propagation_style == :link
               span = tracer.start_root_span(span_name, kind: :consumer, attributes: @mapper.call(payload), links: links)
             end
 
-            tokens.concat(attach_consumer_context(span))
-
-            { span: span, ctx_tokens: tokens }
+            { span: span, ctx_token: attach_consumer_context(span) }
           end
 
           # This method attaches a span to multiple contexts:
           # 1. Registers the ingress span as the top level ActiveJob span.
           #    This is used later to enrich the ingress span in children, e.g. setting span status to error when a child event like `discard` terminates due to an error
           # 2. Registers the ingress span as the "active" span, which is the default behavior of the SDK.
           # @param span [OpenTelemetry::Trace::Span] the currently active span used to record the exception and set the status
-          # @return [Array] Context tokens that must be detached when finished
+          # @return [Numeric] Context token that must be detached when finished
           def attach_consumer_context(span)
             consumer_context = OpenTelemetry::Trace.context_with_span(span)
             internal_context = OpenTelemetry::Instrumentation::ActiveJob.context_with_span(span, parent_context: consumer_context)
 
-            [consumer_context, internal_context].map { |context| OpenTelemetry::Context.attach(context) }
+            OpenTelemetry::Context.attach(internal_context)
           end
         end
       end