Fix opentelemetry-instrumentation-tornado server (request) duration metric calculation (open-telemetry#3486)

Author: devmonkey22

CHANGELOG.md

@@ -37,6 +37,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#3447](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3447))
 - `opentelemetry-instrumentation-botocore` Capture server attributes for botocore API calls
   ([#3448](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3448))
+- `opentelemetry-instrumentation-tornado` Fix server (request) duration metric calculation
+  ([#3486](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3486))
 
 
 ## Version 1.32.0/0.53b0 (2025-04-10)

instrumentation/opentelemetry-instrumentation-tornado/src/opentelemetry/instrumentation/tornado/__init__.py

@@ -199,6 +199,7 @@ def client_response_hook(span, future):
 
 _logger = getLogger(__name__)
 _TraceContext = namedtuple("TraceContext", ["activation", "span", "token"])
+_HANDLER_STATE_KEY = "_otel_state_key"
 _HANDLER_CONTEXT_KEY = "_otel_trace_context_key"
 _OTEL_PATCHED_KEY = "_otel_patched_key"
 
@@ -379,7 +380,10 @@ def _wrap(cls, method_name, wrapper):
 def _prepare(
     tracer, server_histograms, request_hook, func, handler, args, kwargs
 ):
-    server_histograms[_START_TIME] = default_timer()
+    otel_handler_state = {
+        _START_TIME: default_timer()
+    }
+    setattr(handler, _HANDLER_STATE_KEY, otel_handler_state)
 
     request = handler.request
     if _excluded_urls.url_disabled(request.uri):
@@ -593,8 +597,10 @@ def _record_prepare_metrics(server_histograms, handler):
 
 
 def _record_on_finish_metrics(server_histograms, handler, error=None):
+    otel_handler_state = getattr(handler, _HANDLER_STATE_KEY, None) or {}
+    start_time = otel_handler_state.get(_START_TIME, None) or default_timer()
     elapsed_time = round(
-        (default_timer() - server_histograms[_START_TIME]) * 1000
+        (default_timer() - start_time) * 1000
     )
 
     response_size = int(handler._headers.get("Content-Length", 0))