Allow cachedproperty to avoid locking

Under some cirumstances it is ok to recompute
a value when raced to by multiple threads, for these
cases allow the cachedproperty to avoid needing and
using a lock.

Change-Id: Icb71cb5ea280185cfb120671be900435dabcd50b

taskflow/utils/misc.py

@@ -350,8 +350,11 @@ class cachedproperty(object):
     cached property would be stored under '_get_thing' in the self object
     after the first call to 'get_thing' occurs.
     """
-    def __init__(self, fget):
-        self._lock = threading.RLock()
+    def __init__(self, fget=None, require_lock=True):
+        if require_lock:
+            self._lock = threading.RLock()
+        else:
+            self._lock = None
         # If a name is provided (as an argument) then this will be the string
         # to place the cached attribute under if not then it will be the
         # function itself to be wrapped into a property.
@@ -365,10 +368,12 @@ class cachedproperty(object):
             self.__doc__ = None
 
     def __call__(self, fget):
-        # If __init__ received a string then this will be the function to be
-        # wrapped as a property (if __init__ got a function then this will not
-        # be called).
+        # If __init__ received a string or a lock boolean then this will be
+        # the function to be wrapped as a property (if __init__ got a
+        # function then this will not be called).
         self._fget = fget
+        if not self._attr_name:
+            self._attr_name = "_%s" % (fget.__name__)
         self.__doc__ = getattr(fget, '__doc__', None)
         return self
 
@@ -387,13 +392,17 @@ class cachedproperty(object):
         if hasattr(instance, self._attr_name):
             return getattr(instance, self._attr_name)
         else:
-            with self._lock:
-                try:
-                    return getattr(instance, self._attr_name)
-                except AttributeError:
-                    value = self._fget(instance)
-                    setattr(instance, self._attr_name, value)
-                    return value
+            if self._lock is not None:
+                self._lock.acquire()
+            try:
+                return getattr(instance, self._attr_name)
+            except AttributeError:
+                value = self._fget(instance)
+                setattr(instance, self._attr_name, value)
+                return value
+            finally:
+                if self._lock is not None:
+                    self._lock.release()
 
 
 def millis_to_datetime(milliseconds):