Making Features as a singleton for improved caching

python/mxnet/runtime.py

@@ -73,13 +73,19 @@ class Features(collections.OrderedDict):
     """
     OrderedDict of name to Feature
     """
-    def __init__(self):
-        super(Features, self).__init__([(f.name, f) for f in feature_list()])
+    instance = None
+    def __new__(cls):
+        if cls.instance is None:
+            cls.instance = super().__new__(cls)
+        return cls.instance
 
-    def __repr__(self):
-        return str(list(self.values()))
+    def __init__(cls):
+        super(Features, cls).__init__([(f.name, f) for f in feature_list()])
+
+    def __repr__(cls):
+        return str(list(cls.values()))
 
-    def is_enabled(self, feature_name):
+    def is_enabled(cls, feature_name):
         """
         Check for a particular feature by name
 
@@ -94,7 +100,7 @@ def is_enabled(self, feature_name):
             True if it's enabled, False if it's disabled, RuntimeError if the feature is not known
         """
         feature_name = feature_name.upper()
-        if feature_name not in self:
+        if feature_name not in cls:
             raise RuntimeError("Feature '{}' is unknown, known features are: {}".format(
-                feature_name, list(self.keys())))
-        return self[feature_name].enabled
+                feature_name, list(cls.keys())))
+        return cls[feature_name].enabled

tests/python/unittest/test_runtime.py

@@ -21,12 +21,20 @@
 from mxnet.base import MXNetError
 from nose.tools import *
 
+
 def test_features():
     features = Features()
     print(features)
     ok_('CUDA' in features)
     ok_(len(features) >= 30)
 
+
+def test_is_singleton():
+    x = Features()
+    y = Features()
+    assert x is y
+
+
 def test_is_enabled():
     features = Features()
     for f in features:
@@ -35,6 +43,7 @@ def test_is_enabled():
         else:
             ok_(not features.is_enabled(f))
 
+
 @raises(RuntimeError)
 def test_is_enabled_not_existing():
     features = Features()