Bug Fix: Defensively copy context entities

Before this change, concurrent async tasks would all share the same
instance of the entities list. This change makes it so they each get
their own copy of the list. This matters because the recorder modifies
the list in place, which makes it so concurrent subtasks have the
wrong parent subsegment.

Author: tyler-dodge

aws_xray_sdk/core/async_context.py

@@ -1,5 +1,6 @@
 import asyncio
 import sys
+import copy
 
 from .context import Context as _Context
 
@@ -108,6 +109,13 @@ def task_factory(loop, coro):
     else:
         current_task = asyncio.Task.current_task(loop=loop)
     if current_task is not None and hasattr(current_task, 'context'):
-        setattr(task, 'context', current_task.context)
+        if current_task.context['entities']:
+            # Defensively copying because recorder modifies the list in place.
+            new_context = copy.copy(current_task.context)
+            new_context['entities'] = [item for item in current_task.context['entities']]
+        else:
+            # no reason to copy if there's no entities list.
+            new_context = current_task.context
+        setattr(task, 'context', new_context)
 
     return task