[Python-checkins] cpython (2.7): Backport early-out 91259f061cfb to reduce the cost of bb1a2944bcb6

[raymond.hettinger]

https://hg.python.org/cpython/rev/37aee118e1a3
changeset:   98578:37aee118e1a3
branch:      2.7
parent:      98572:60c44a09c5fc
user:        Raymond Hettinger <python at rcn.com>
date:        Tue Oct 06 23:12:02 2015 -0400
summary:
  Backport early-out 91259f061cfb to reduce the cost of bb1a2944bcb6

files:
  Modules/_collectionsmodule.c |  6 +++++-
  1 files changed, 5 insertions(+), 1 deletions(-)


diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -651,6 +651,9 @@
     Py_ssize_t n;
     PyObject *item;
 
+    if (Py_SIZE(deque) == 0)
+        return;
+
     /* During the process of clearing a deque, decrefs can cause the
        deque to mutate.  To avoid fatal confusion, we have to make the
        deque empty before clearing the blocks and never refer to
@@ -1083,7 +1086,8 @@
         }
     }
     deque->maxlen = maxlen;
-    deque_clear(deque);
+    if (Py_SIZE(deque) > 0)
+        deque_clear(deque);
     if (iterable != NULL) {
         PyObject *rv = deque_extend(deque, iterable);
         if (rv == NULL)

-- 
Repository URL: https://hg.python.org/cpython