fix: use start and end times from langchain (#304)

python/instrumentation/openinference-instrumentation-langchain/src/openinference/instrumentation/langchain/_tracer.py

@@ -4,7 +4,7 @@
 import time
 import traceback
 from copy import deepcopy
-from datetime import datetime
+from datetime import datetime, timezone
 from enum import Enum
 from itertools import chain
 from threading import RLock
@@ -86,7 +86,14 @@ def _start_trace(self, run: Run) -> None:
                 and (parent := self._runs.get(parent_run_id))
                 else None
             )
-        span = self._tracer.start_span(name=run.name, context=parent_context)
+        # We can't use real time because the handler may be
+        # called in a background thread.
+        start_time_utc_nano = _as_utc_nano(run.start_time)
+        span = self._tracer.start_span(
+            name=run.name,
+            context=parent_context,
+            start_time=start_time_utc_nano,
+        )
         context = trace_api.set_span_in_context(span)
         # The following line of code is commented out to serve as a reminder that in a system
         # of callbacks, attaching the context can be hazardous because there is no guarantee
@@ -111,7 +118,10 @@ def _end_trace(self, run: Run) -> None:
                 _update_span(span, run)
             except Exception:
                 logger.exception("Failed to update span with run data.")
-            span.end()
+            # We can't use real time because the handler may be
+            # called in a background thread.
+            end_time_utc_nano = _as_utc_nano(run.end_time) if run.end_time else None
+            span.end(end_time=end_time_utc_nano)
 
     def _persist_run(self, run: Run) -> None:
         pass
@@ -583,6 +593,10 @@ def default(self, obj: Any) -> Any:
             return str(obj)
 
 
+def _as_utc_nano(dt: datetime) -> int:
+    return int(dt.astimezone(timezone.utc).timestamp() * 1_000_000_000)
+
+
 DOCUMENT_CONTENT = DocumentAttributes.DOCUMENT_CONTENT
 DOCUMENT_ID = DocumentAttributes.DOCUMENT_ID
 DOCUMENT_METADATA = DocumentAttributes.DOCUMENT_METADATA