perf(co): retrieve context from spans

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_context(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_context(span.context)):
                     # Create a snapshot
                     snapshot = Snapshot(
                         probe=ExitSpanProbe.from_frame(frame),

ddtrace/debugging/_session.py

@@ -78,6 +78,10 @@ def get_probe_count(self, probe_id: str) -> int:
     def from_trace(cls) -> t.List["Session"]:
         return SessionManager.get_sessions_for_trace()
 
+    @classmethod
+    def from_context(cls, context) -> t.List["Session"]:
+        return SessionManager.get_sessions_for_context(context)
+
     @classmethod
     def lookup(cls, ident: SessionId) -> t.Optional["Session"]:
         return SessionManager.lookup_session(ident)
@@ -119,6 +123,13 @@ def get_sessions_for_trace(cls) -> t.List[Session]:
 
         return list(cls._sessions_trace_map.get(context, {}).values())
 
+    @classmethod
+    def get_sessions_for_context(cls, context) -> t.List[Session]:
+        if context is None:
+            return []
+
+        return list(cls._sessions_trace_map.get(context, {}).values())
+
     @classmethod
     def lookup_session(cls, ident: SessionId) -> t.Optional[Session]:
         context = tracer.current_trace_context()