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fix(rack): fiber-safe context detachment in EventHandler #2130

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fix(rack): fiber-safe context detachment in EventHandler #2130

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17 changes: 12 additions & 5 deletions instrumentation/rack/lib/opentelemetry/instrumentation/rack/middlewares/dup/event_handler.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ module Dup
class EventHandler
include ::Rack::Events::Abstract

OTEL_TOKEN_AND_SPAN = 'otel.rack.token_and_span'
OTEL_CONTEXT_INFO = 'otel.context_info'
EMPTY_HASH = {}.freeze

# Creates a server span for this current request using the incoming parent context
Expand All @@ -62,7 +62,8 @@ def on_start(request, _)
span = create_span(parent_context, request)
span_ctx = OpenTelemetry::Trace.context_with_span(span, parent_context: parent_context)
rack_ctx = OpenTelemetry::Instrumentation::Rack.context_with_span(span, parent_context: span_ctx)
request.env[OTEL_TOKEN_AND_SPAN] = [OpenTelemetry::Context.attach(rack_ctx), span]
token = OpenTelemetry::Context.attach(rack_ctx)
request.env[OTEL_CONTEXT_INFO] = [Fiber.current, token, span]
rescue StandardError => e
OpenTelemetry.handle_error(exception: e)
end
Expand Down Expand Up @@ -209,11 +210,17 @@ def request_span_attributes(env)
end

def detach_context(request)
return nil unless request.env[OTEL_TOKEN_AND_SPAN]
otel_context_info = request.env[OTEL_CONTEXT_INFO]
return unless otel_context_info

token, span = request.env[OTEL_TOKEN_AND_SPAN]
original_fiber, token, span = otel_context_info
span.finish
OpenTelemetry::Context.detach(token)

if Fiber.current.equal?(original_fiber)
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@arielvalentin arielvalentin Apr 18, 2026

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Could you share more details about how this could happen?

What application server are you using that invokes the rack events in different fibers?

OpenTelemetry::Context.detach(token)
else
OpenTelemetry.logger.debug { '[rack] Skipping context detach: response processed in different fiber than request.' }
end
rescue StandardError => e
OpenTelemetry.handle_error(exception: e)
end
Expand Down
17 changes: 12 additions & 5 deletions instrumentation/rack/lib/opentelemetry/instrumentation/rack/middlewares/old/event_handler.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ module Old
class EventHandler
include ::Rack::Events::Abstract

OTEL_TOKEN_AND_SPAN = 'otel.rack.token_and_span'
OTEL_CONTEXT_INFO = 'otel.context_info'
EMPTY_HASH = {}.freeze

# Creates a server span for this current request using the incoming parent context
Expand All @@ -62,7 +62,8 @@ def on_start(request, _)
span = create_span(parent_context, request)
span_ctx = OpenTelemetry::Trace.context_with_span(span, parent_context: parent_context)
rack_ctx = OpenTelemetry::Instrumentation::Rack.context_with_span(span, parent_context: span_ctx)
request.env[OTEL_TOKEN_AND_SPAN] = [OpenTelemetry::Context.attach(rack_ctx), span]
token = OpenTelemetry::Context.attach(rack_ctx)
request.env[OTEL_CONTEXT_INFO] = [Fiber.current, token, span]
rescue StandardError => e
OpenTelemetry.handle_error(exception: e)
end
Expand Down Expand Up @@ -198,11 +199,17 @@ def request_span_attributes(env)
end

def detach_context(request)
return nil unless request.env[OTEL_TOKEN_AND_SPAN]
otel_context_info = request.env[OTEL_CONTEXT_INFO]
return unless otel_context_info

token, span = request.env[OTEL_TOKEN_AND_SPAN]
original_fiber, token, span = otel_context_info
span.finish
OpenTelemetry::Context.detach(token)

if Fiber.current.equal?(original_fiber)
OpenTelemetry::Context.detach(token)
else
OpenTelemetry.logger.debug { '[rack] Skipping context detach: response processed in different fiber than request.' }
end
rescue StandardError => e
OpenTelemetry.handle_error(exception: e)
end
Expand Down
17 changes: 12 additions & 5 deletions ...mentation/rack/lib/opentelemetry/instrumentation/rack/middlewares/stable/event_handler.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ module Stable
class EventHandler
include ::Rack::Events::Abstract

OTEL_TOKEN_AND_SPAN = 'otel.rack.token_and_span'
OTEL_CONTEXT_INFO = 'otel.context_info'
EMPTY_HASH = {}.freeze

# Creates a server span for this current request using the incoming parent context
Expand All @@ -62,7 +62,8 @@ def on_start(request, _)
span = create_span(parent_context, request)
span_ctx = OpenTelemetry::Trace.context_with_span(span, parent_context: parent_context)
rack_ctx = OpenTelemetry::Instrumentation::Rack.context_with_span(span, parent_context: span_ctx)
request.env[OTEL_TOKEN_AND_SPAN] = [OpenTelemetry::Context.attach(rack_ctx), span]
token = OpenTelemetry::Context.attach(rack_ctx)
request.env[OTEL_CONTEXT_INFO] = [Fiber.current, token, span]
rescue StandardError => e
OpenTelemetry.handle_error(exception: e)
end
Expand Down Expand Up @@ -197,11 +198,17 @@ def request_span_attributes(env)
end

def detach_context(request)
return nil unless request.env[OTEL_TOKEN_AND_SPAN]
otel_context_info = request.env[OTEL_CONTEXT_INFO]
return unless otel_context_info

token, span = request.env[OTEL_TOKEN_AND_SPAN]
original_fiber, token, span = otel_context_info
span.finish
OpenTelemetry::Context.detach(token)

if Fiber.current.equal?(original_fiber)
OpenTelemetry::Context.detach(token)
else
OpenTelemetry.logger.debug { '[rack] Skipping context detach: response processed in different fiber than request.' }
end
rescue StandardError => e
OpenTelemetry.handle_error(exception: e)
end
Expand Down
34 changes: 34 additions & 0 deletions ...tation/rack/test/opentelemetry/instrumentation/rack/middlewares/dup/event_handler_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -508,4 +508,38 @@ class EventHandlerError < StandardError
_(proxy_event).must_be_nil
end
end

describe 'cross-fiber context detachment' do
it 'finishes span without error when on_finish is called from different fiber' do
request = Rack::MockRequest.env_for('/')
rack_request = Rack::Request.new(request)
response = Rack::Response.new

fiber1 = Fiber.new do
handler.on_start(rack_request, nil)
Fiber.yield
end
fiber1.resume

fiber2 = Fiber.new do
handler.on_finish(rack_request, response)
end
fiber2.resume

_(finished_spans.size).must_equal 1
_(rack_span.name).must_equal 'GET'
end

it 'detaches context normally when same fiber' do
request = Rack::MockRequest.env_for('/')
rack_request = Rack::Request.new(request)
response = Rack::Response.new

handler.on_start(rack_request, nil)
handler.on_finish(rack_request, response)

_(finished_spans.size).must_equal 1
_(rack_span.name).must_equal 'GET'
end
end
end
34 changes: 34 additions & 0 deletions ...tation/rack/test/opentelemetry/instrumentation/rack/middlewares/old/event_handler_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -483,4 +483,38 @@ class EventHandlerError < StandardError
_(proxy_event).must_be_nil
end
end

describe 'cross-fiber context detachment' do
it 'finishes span without error when on_finish is called from different fiber' do
request = Rack::MockRequest.env_for('/')
rack_request = Rack::Request.new(request)
response = Rack::Response.new

fiber1 = Fiber.new do
handler.on_start(rack_request, nil)
Fiber.yield
end
fiber1.resume

fiber2 = Fiber.new do
handler.on_finish(rack_request, response)
end
fiber2.resume

_(finished_spans.size).must_equal 1
_(rack_span.name).must_equal 'HTTP GET'
end

it 'detaches context normally when same fiber' do
request = Rack::MockRequest.env_for('/')
rack_request = Rack::Request.new(request)
response = Rack::Response.new

handler.on_start(rack_request, nil)
handler.on_finish(rack_request, response)

_(finished_spans.size).must_equal 1
_(rack_span.name).must_equal 'HTTP GET'
end
end
end
34 changes: 34 additions & 0 deletions ...ion/rack/test/opentelemetry/instrumentation/rack/middlewares/stable/event_handler_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -479,4 +479,38 @@ class EventHandlerError < StandardError
_(proxy_event).must_be_nil
end
end

describe 'cross-fiber context detachment' do
it 'finishes span without error when on_finish is called from different fiber' do
request = Rack::MockRequest.env_for('/')
rack_request = Rack::Request.new(request)
response = Rack::Response.new

fiber1 = Fiber.new do
handler.on_start(rack_request, nil)
Fiber.yield
end
fiber1.resume

fiber2 = Fiber.new do
handler.on_finish(rack_request, response)
end
fiber2.resume

_(finished_spans.size).must_equal 1
_(rack_span.name).must_equal 'GET'
end

it 'detaches context normally when same fiber' do
request = Rack::MockRequest.env_for('/')
rack_request = Rack::Request.new(request)
response = Rack::Response.new

handler.on_start(rack_request, nil)
handler.on_finish(rack_request, response)

_(finished_spans.size).must_equal 1
_(rack_span.name).must_equal 'GET'
end
end
end
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