Disallow nested parallel blocks and propagate sharing attributes

Cython/Compiler/ParseTreeTransforms.py

@@ -978,6 +978,10 @@ class ParallelRangeTransform(CythonTransform, SkipDeclarations):
     # Keep track of whether we are in a parallel range section
     in_prange = False
 
+    # One of 'prange' or 'with parallel'. This is used to disallow closely
+    # nested 'with parallel:' blocks
+    state = None
+
     directive_to_node = {
         u"cython.parallel.parallel": Nodes.ParallelWithBlockNode,
         # u"cython.parallel.threadsavailable": ExprNodes.ParallelThreadsAvailableNode,
@@ -1070,9 +1074,16 @@ class ParallelRangeTransform(CythonTransform, SkipDeclarations):
                 # There was an error, stop here and now
                 return None
 
+            if self.state == 'parallel with':
+                error(node.manager.pos,
+                      "Closely nested 'with parallel:' blocks are disallowed")
+
+            self.state = 'parallel with'
             self.visit(node.body)
+            self.state = None
 
             newnode = Nodes.ParallelWithBlockNode(node.pos, body=node.body)
+
         else:
             newnode = node
 
@@ -1088,6 +1099,7 @@ class ParallelRangeTransform(CythonTransform, SkipDeclarations):
         was_in_prange = self.in_prange
         self.in_prange = isinstance(node.iterator.sequence,
                                     Nodes.ParallelRangeNode)
+        previous_state = self.state
 
         if self.in_prange:
             # This will replace the entire ForInStatNode, so copy the
@@ -1104,11 +1116,13 @@ class ParallelRangeTransform(CythonTransform, SkipDeclarations):
                 error(node.target.pos,
                       "Can only iterate over an iteration variable")
 
-        self.visit(node.body)
+            self.state = 'prange'
 
+        self.visit(node.body)
+        self.state = previous_state
         self.in_prange = was_in_prange
-        self.visit(node.else_clause)
 
+        self.visit(node.else_clause)
         return node
 
     def ensure_not_in_prange(name):

tests/errors/e_cython_parallel.pyx

@@ -30,6 +30,12 @@ with nogil, cython.parallel.parallel:
     for x[1] in prange(10):
         pass
 
+    for x in prange(10):
+        pass
+
+    with cython.parallel.parallel:
+        pass
+
 _ERRORS = u"""
 e_cython_parallel.pyx:3:8: cython.parallel.parallel is not a module
 e_cython_parallel.pyx:4:0: No such directive: cython.parallel.something
@@ -41,4 +47,6 @@ e_cython_parallel.pyx:18:19: Invalid schedule argument to prange: 'invalid_sched
 e_cython_parallel.pyx:21:5: The parallel section may only be used without the GIL
 e_cython_parallel.pyx:27:10: target may not be a Python object as we don't have the GIL
 e_cython_parallel.pyx:30:9: Can only iterate over an iteration variable
+e_cython_parallel.pyx:33:10: Must be of numeric type, not int *
+e_cython_parallel.pyx:36:24: Closely nested 'with parallel:' blocks are disallowed
 """

tests/run/parallel.pyx

@@ -43,30 +43,25 @@ def test_descending_prange():
 
     return sum
 
-def test_nested_prange():
+def test_propagation():
     """
-    Reduction propagation is not (yet) supported.
-
-    >>> test_nested_prange()
-    50
+    >>> test_propagation()
+    (9, 9, 9, 9, 450, 450)
     """
-    cdef int i, j
-    cdef int sum = 0
-
-    for i in prange(5, nogil=True):
-        for j in prange(5):
-            sum += i
-
-    # The value of sum is undefined here
+    cdef int i, j, x, y
+    cdef int sum1 = 0, sum2 = 0
 
-    sum = 0
+    for i in prange(10, nogil=True):
+        for j in prange(10):
+            sum1 += i
 
-    for i in prange(5, nogil=True):
-        for j in prange(5):
-            sum += i
-        sum += 0
+    with nogil, cython.parallel.parallel:
+        for x in prange(10):
+            with cython.parallel.parallel:
+                for y in prange(10):
+                    sum2 += y
 
-    return sum
+    return i, j, x, y, sum1, sum2
 
 
 def test_parallel():
@@ -225,11 +220,11 @@ def test_parallel_numpy_arrays():
             print i
         return
 
-    x = numpy.zeros(10, dtype=np.int)
+    x = numpy.zeros(10, dtype=numpy.int)
 
     for i in prange(x.shape[0], nogil=True):
         x[i] = i - 5
 
     for i in x:
-        print x
+        print i