From 6d5501d506c70333a5763cae87705feab20a53d7 Mon Sep 17 00:00:00 2001
From: Graham Dumpleton <Graham.Dumpleton@gmail.com>
Date: Tue, 17 Sep 2013 21:57:57 +1000
Subject: [PATCH] Added a synchronized decorator for thread mutex locking
 around functions, class instances and classes.

---
 src/__init__.py   |  2 +-
 src/decorators.py | 51 ++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/src/__init__.py b/src/__init__.py
index dfdf254..2e1f967 100644
--- a/src/__init__.py
+++ b/src/__init__.py
@@ -2,4 +2,4 @@ __version_info__ = ('1', '1', '0')
 __version__ = '.'.join(__version_info__)
 
 from .wrappers import ObjectProxy, FunctionWrapper, WeakFunctionProxy
-from .decorators import decorator
+from .decorators import decorator, synchronized
diff --git a/src/decorators.py b/src/decorators.py
index 19ef9f4..b98fcef 100644
--- a/src/decorators.py
+++ b/src/decorators.py
@@ -1,4 +1,5 @@
-"""This module implements decorators for implementing other decorators.
+"""This module implements decorators for implementing other decorators
+as well as some commonly used decorators.
 
 """
 
@@ -7,6 +8,7 @@ from . import six
 from functools import wraps, partial
 from inspect import getargspec, ismethod
 from collections import namedtuple
+from threading import Lock, RLock
 
 if not six.PY2:
     from inspect import signature
@@ -120,3 +122,50 @@ def decorator(wrapper=None, adapter=None):
         # arguments.
 
         return partial(decorator, adapter=adapter)
+
+# Decorator for implementing thread synchronisation on functions and
+# objects.
+
+@decorator
+def synchronized(wrapped, instance, args, kwargs):
+    # Use the instance as the context if function was bound.
+
+    if instance is not None:
+        context = instance
+    else:
+        context = wrapped
+
+    # Retrieve the lock for the specific context.
+
+    lock = getattr(context, '_synchronized_lock', None)
+
+    if lock is None:
+        # There is no existing lock defined for the context we
+        # are dealing with so we need to create one. This needs
+        # to be done in a way to guarantee there is only one
+        # created, even if multiple threads try and create it at
+        # the same time. We can't always use the setdefault()
+        # method on the __dict__ for the context. This is the
+        # case where the context is a class, as __dict__ is
+        # actually a dictproxy. What we therefore do is use a
+        # meta lock on this wrapper itself, to control the
+        # creation and assignment of the lock attribute against
+        # the context.
+
+        meta_lock = vars(synchronized).setdefault(
+                '_synchronized_meta_lock', Lock())
+
+        with meta_lock:
+            # We need to check again for whether the lock we want
+            # exists in case two threads were trying to create it
+            # at the same time and were competing to create the
+            # meta lock.
+
+            lock = getattr(context, '_synchronized_lock', None)
+
+            if lock is None:
+                lock = RLock()
+                setattr(context, '_synchronized_lock', lock)
+
+    with lock:
+        return wrapped(*args, **kwargs)