lightstep/lightstep-tracer-ruby

module LightStep
  # ScopeManager represents an OpenTracing ScopeManager
  #
  # See http://www.opentracing.io for more information.
  #
  # The ScopeManager interface abstracts both the activation of Span instances
  # via ScopeManager#activate and access to an active Span/Scope via
  # ScopeManager#active
  #
  class ScopeManager
    # Make a span instance active.
    #
    # @param span [Span] the Span that should become active
    # @param finish_on_close [Boolean] whether the Span should automatically be
    #   finished when Scope#close is called
    # @return [Scope] instance to control the end of the active period for the
    #  Span. It is a programming error to neglect to call Scope#close on the
    #  returned instance.
    def activate(span:, finish_on_close: true)
      return active if active && active.span == span
      LightStep::Scope.new(manager: self, span: span, finish_on_close: finish_on_close).tap do |scope|
        add_scope(scope)
      end
    end

    # @return [Scope] the currently active Scope which can be used to access the
    # currently active Span.
    #
    # If there is a non-null Scope, its wrapped Span becomes an implicit parent
    # (as Reference#CHILD_OF) of any newly-created Span at Tracer#start_active_span
    # or Tracer#start_span time.
    def active
      scopes.last
    end

    def deactivate
      scopes.pop
    end

    private

    def scopes
      Thread.current[object_id.to_s] || []
    end

    def add_scope(scope)
      if Thread.current[object_id.to_s].nil?
        Thread.current[object_id.to_s] = [scope]
      else
        Thread.current[object_id.to_s] << scope
      end
    end
  end
end