use freelists for closure classes

Cython/Compiler/Options.py

@@ -67,6 +67,9 @@ cimport_from_pyx = False
 # slices are passed by value and involve a lot of copying
 buffer_max_dims = 8
 
+# Number of function closure instances to keep in a freelist (0: no freelists)
+closure_freelist_size = 8
+
 # Declare compiler directives
 directive_defaults = {
     'boundscheck' : True,

Cython/Compiler/ParseTreeTransforms.py

@@ -2248,6 +2248,8 @@ class CreateClosureClasses(CythonTransform):
         func_scope.scope_class = entry
         class_scope = entry.type.scope
         class_scope.is_internal = True
+        if Options.closure_freelist_size:
+            class_scope.directives['freelist'] = Options.closure_freelist_size
 
         if from_closure:
             assert cscope.is_closure_scope