Avoid circular references in StackContext and ExceptionStackContext.

diff --git a/tornado/stack_context.py b/tornado/stack_context.py
index 8804d42d88a096a591ff8e3d9e9aa3e6c888fa49..ec94a1b8e1ae6c735f93aeeca3bbf715d10bbdff 100644 (file)
--- a/tornado/stack_context.py
+++ b/tornado/stack_context.py
@@ -151,6 +151,9 @@ class StackContext(object):
                     'stack_context inconsistency (may be caused by yield '
                     'within a "with StackContext" block)')
 
+            # Break up a reference to itself to allow for faster GC on CPython.
+            self.new_contexts = None
+
 
 class ExceptionStackContext(object):
     """Specialization of StackContext for exception handling.
@@ -190,6 +193,9 @@ class ExceptionStackContext(object):
                     'stack_context inconsistency (may be caused by yield '
                     'within a "with StackContext" block)')
 
+            # Break up a reference to itself to allow for faster GC on CPython.
+            self.new_contexts = None
+
 
 class NullContext(object):
     """Resets the `StackContext`.