Merge branch 'fenics_master'

Author: Andrew McRae

ufl/core/compute_expr_hash.py

@@ -0,0 +1,59 @@
+"""Non-recursive traversal based hash computation algorithm.
+
+Fast iteration over nodes in an Expr DAG to compute
+memoized hashes for all unique nodes.
+"""
+
+# Copyright (C) 2015 Martin Sandve Alnes
+#
+# This file is part of UFL.
+#
+# UFL is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# UFL is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with UFL. If not, see <http://www.gnu.org/licenses/>.
+
+
+# This limits the _depth_ of expression trees
+_recursion_limit_ = 6400 # should be enough for everyone
+
+
+def compute_expr_hash(expr):
+    """Compute hashes of expr and all its nodes efficiently without using Python recursion."""
+    if expr._hash is not None:
+        return expr._hash
+
+    stack = [None]*_recursion_limit_
+    stacksize = 0
+
+    ops = expr.ufl_operands
+    stack[stacksize] = [expr, ops, len(ops)]
+    stacksize += 1
+
+    while stacksize > 0:
+        entry = stack[stacksize - 1]
+        e = entry[0]
+        if e._hash is not None:
+            # cutoff: don't need to visit children when hash has previously been computed
+            stacksize -= 1
+        elif entry[2] == 0:
+            # all children consumed: trigger memoized hash computation
+            e._hash = e._ufl_compute_hash_()
+            stacksize -= 1
+        else:
+            # add children to stack to hash them first
+            entry[2] -= 1
+            o = entry[1][entry[2]]
+            oops = o.ufl_operands
+            stack[stacksize] = [o, oops, len(oops)]
+            stacksize += 1
+
+    return expr._hash

ufl/core/expr.py

@@ -116,11 +116,11 @@ def __init__(self):
     def __del__(self):
         pass
 
-    def __hash__(self):
-        if self._hash is None:
-            self._hash = self._ufl_compute_hash_()
-        return self._hash
-
+    # This shows the principal behaviour of the hash function attached in ufl_type:
+    #def __hash__(self):
+    #    if self._hash is None:
+    #        self._hash = self._ufl_compute_hash_()
+    #    return self._hash
 
     # --- Type traits are added to subclasses by the ufl_type class decorator ---
 

ufl/core/ufl_type.py

@@ -1,6 +1,7 @@
 
 
 from ufl.core.expr import Expr
+from ufl.core.compute_expr_hash import compute_expr_hash
 
 from ufl.common import camel2underscore, EmptyDict
 
@@ -216,6 +217,7 @@ def ufl_type(is_abstract=False,
              is_restriction=False,
              is_evaluation=False,
              is_differential=None,
+             use_default_hash=True,
              num_ops=None,
              inherit_shape_from_operand=None,
              inherit_indices_from_operand=None,
@@ -311,9 +313,10 @@ def _ufl_expr_rbinop_(self, other):
 
         # Make sure every non-abstract class has its own __hash__ and __eq__.
         # Python 3 will set __hash__ to None if cls has __eq__, but we've
-        # implemented it in Expr and want to inherit it.
-        if cls.__hash__ is None:
-            cls.__hash__ = Expr.__hash__
+        # implemented it in a separate function and want to inherit/use that
+        # for all types. Allow overriding by setting use_default_hash=False.
+        if use_default_hash:
+            cls.__hash__ = compute_expr_hash
 
         # NB! This function conditionally adds some methods to the class!
         # This approach significantly reduces the amount of small functions to

ufl/corealg/traversal.py

@@ -21,7 +21,10 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with UFL. If not, see <http://www.gnu.org/licenses/>.
 
-_recursion_limit_ = 2000
+
+# This limits the _depth_ of expression trees
+_recursion_limit_ = 6400 # should be enough for everyone
+
 
 def pre_traversal(expr):
     """Yields o for each tree node o in expr, parent before child."""