Merge branch 'master' into feature.override-asset-with-absolute-path

1 files changed, 6 insertions, 2 deletions

diff --git a/docs/narr/hooks.rst b/docs/narr/hooks.rst
index f2542f1d7..4da36e730 100644
--- a/docs/narr/hooks.rst
+++ b/docs/narr/hooks.rst
@@ -985,7 +985,7 @@ Creating a Tween
 
 To create a tween, you must write a "tween factory".  A tween factory
 must be a globally importable callable which accepts two arguments:
-``handler`` and ``registry``.  ``handler`` will be the either the main
+``handler`` and ``registry``.  ``handler`` will be either the main
 Pyramid request handling function or another tween.  ``registry`` will be the
 Pyramid :term:`application registry` represented by this Configurator.  A
 tween factory must return the tween (a callable object) when it is called.
@@ -1023,7 +1023,7 @@ method:
     :linenos:
 
     class simple_tween_factory(object):
-        def __init__(handler, registry):
+        def __init__(self, handler, registry):
             self.handler = handler
             self.registry = registry
 
@@ -1040,6 +1040,10 @@ method:
 
             return response
 
+You should avoid mutating any state on the tween instance. The tween is
+invoked once per request and any shared mutable state needs to be carefully
+handled to avoid any race conditions.
+
 The closure style performs slightly better and enables you to conditionally
 omit the tween from the request processing pipeline (see the following timing
 tween example), whereas the class style makes it easier to have shared mutable