perf(co): retrieve context from spans (#14929)

We retrieve the context object that we use to link sessions to traces
directly from span objects to avoid triggering more expensive tracer
logic by querying for the current running context from the tracer itself

Author: P403n1x87

ddtrace/debugging/_origin/span.py

@@ -166,7 +166,7 @@ def _close_signal(self, retval=None, exc_info=(None, None, None)):
 
         # Check if we have any level 2 debugging sessions running for the
         # current trace
-        if any(s.level >= 2 for s in Session.from_trace()):
+        if any(s.level >= 2 for s in Session.from_trace(root.context or span.context)):
             # Create a snapshot
             snapshot = Snapshot(
                 probe=self.location.probe,
@@ -270,7 +270,7 @@ def on_span_start(self, span: Span) -> None:
 
                 # Check if we have any level 2 debugging sessions running for
                 # the current trace
-                if any(s.level >= 2 for s in Session.from_trace()):
+                if any(s.level >= 2 for s in Session.from_trace(span.context)):
                     # Create a snapshot
                     snapshot = Snapshot(
                         probe=ExitSpanProbe.from_frame(frame),

ddtrace/debugging/_session.py

@@ -75,8 +75,8 @@ def get_probe_count(self, probe_id: str) -> int:
         return self._counts.get(probe_id, 0)
 
     @classmethod
-    def from_trace(cls) -> t.List["Session"]:
-        return SessionManager.get_sessions_for_trace()
+    def from_trace(cls, trace_context: t.Optional[t.Any] = None) -> t.List["Session"]:
+        return SessionManager.get_sessions_for_trace(trace_context)
 
     @classmethod
     def lookup(cls, ident: SessionId) -> t.Optional["Session"]:
@@ -112,12 +112,12 @@ def unlink_session_from_trace(cls, session, trace_context: t.Optional[t.Any] = N
         cls._sessions_trace_map.get(context, {}).pop(session.ident, None)
 
     @classmethod
-    def get_sessions_for_trace(cls) -> t.List[Session]:
-        context = tracer.current_trace_context()
-        if context is None:
-            return []
-
-        return list(cls._sessions_trace_map.get(context, {}).values())
+    def get_sessions_for_trace(cls, trace_context: t.Optional[t.Any] = None) -> t.List[Session]:
+        return (
+            list(cls._sessions_trace_map.get(context, {}).values())
+            if cls._sessions_trace_map and (context := (trace_context or tracer.current_trace_context())) is not None
+            else []
+        )
 
     @classmethod
     def lookup_session(cls, ident: SessionId) -> t.Optional[Session]: