StackContext speedups: special-case some common situations,

and stop using function attributes.

tornado/stack_context.py

@@ -48,6 +48,8 @@ def die_on_error():
 
 from __future__ import with_statement
 
+from types import NoneType
+
 import contextlib
 import functools
 import itertools
@@ -135,6 +137,9 @@ def __enter__(self):
     def __exit__(self, type, value, traceback):
         _state.contexts = self.old_contexts
 
+class _StackContextWrapper(functools.partial):
+    pass
+
 def wrap(fn):
     '''Returns a callable object that will resore the current StackContext
     when executed.
@@ -143,18 +148,21 @@ def wrap(fn):
     different execution context (either in a different thread or
     asynchronously in the same thread).
     '''
-    if fn is None:
-      return None
     # functools.wraps doesn't appear to work on functools.partial objects
     #@functools.wraps(fn)
     def wrapped(callback, contexts, *args, **kwargs):
+        if contexts is _state.contexts or not contexts:
+            callback(*args, **kwargs)
+            return
+        if not _state.contexts:
+            new_contexts = [cls(arg) for (cls, arg) in contexts]
         # If we're moving down the stack, _state.contexts is a prefix
         # of contexts.  For each element of contexts not in that prefix,
         # create a new StackContext object.
         # If we're moving up the stack (or to an entirely different stack),
         # _state.contexts will have elements not in contexts.  Use
         # NullContext to clear the state and then recreate from contexts.
-        if (len(_state.contexts) > len(contexts) or
+        elif (len(_state.contexts) > len(contexts) or
             any(a[1] is not b[1]
                 for a, b in itertools.izip(_state.contexts, contexts))):
             # contexts have been removed or changed, so start over
@@ -171,10 +179,7 @@ def wrapped(callback, contexts, *args, **kwargs):
                 callback(*args, **kwargs)
         else:
             callback(*args, **kwargs)
-    if getattr(fn, 'stack_context_wrapped', False):
+    if isinstance(fn, (_StackContextWrapper, NoneType)):
         return fn
-    contexts = _state.contexts
-    result = functools.partial(wrapped, fn, contexts)
-    result.stack_context_wrapped = True
-    return result
+    return _StackContextWrapper(wrapped, fn, _state.contexts)