BUG FIX: state_updates should be initialized in MRG_RandomStreams.__init__ to

theano/sandbox/rng_mrg.py

@@ -637,10 +637,6 @@ def guess_n_streams(size, warn=True):
 class MRG_RandomStreams(object):
     """Module component with similar interface to numpy.random (numpy.random.RandomState)"""
 
-    state_updates = []
-    """A list of pairs of the form (input_r, output_r), representing the
-    update rules of all the random states generated by this RandomStreams"""
-
     def updates(self):
         return list(self.state_updates)
 
@@ -655,6 +651,10 @@ class MRG_RandomStreams(object):
             M2 = 2147462579, and not all 0.
 
         """
+        # A list of pairs of the form (input_r, output_r), representing the
+        # update rules of all the random states generated by this RandomStreams"""
+        self.state_updates = []
+
         super(MRG_RandomStreams, self).__init__()
         if isinstance(seed, int):
             if seed == 0:

theano/sandbox/test_rng_mrg.py

@@ -677,3 +677,23 @@ class T_MRG(unittest.TestCase):
             self.assertRaises(ValueError, R.binomial, size)
             self.assertRaises(ValueError, R.multinomial, size, 1, [])
             self.assertRaises(ValueError, R.normal, size)
+
+def test_multiple_rng():
+    """
+    Test that we can have multiple random number generators in parallel, and
+    that we can replicate the stream of one with another. This is meant to fix a
+    previous bug in rng_mrg.MRG_RandomStreams where state_updates was
+    initialized as a class variable, instead of in the __init__ method. This
+    would cause all MRG_RandomStreams objects to share the same state.
+    """
+    rng1 = MRG_RandomStreams(1234)
+    var1 = theano.shared(numpy.ones(1))
+    out1 = rng1.uniform(size=(1,))
+    f1 = theano.function([], out1, updates={var1: out1})
+    assert len(rng1.state_updates) == 1
+    
+    rng2 = MRG_RandomStreams(1234)
+    out2 = rng2.uniform(size=(1,))
+    f2 = theano.function([], out2, updates={var1: out2})
+    assert len(rng1.state_updates) == 1
+    assert len(rng2.state_updates) == 1