set: make set thread-safe

Author: colesbury

Lib/test/test_sys.py

@@ -1497,7 +1497,7 @@ def delx(self): del self.__x
         # frozenset
         PySet_MINSIZE = 8
         samples = [[], range(10), range(50)]
-        s = size('3nP' + PySet_MINSIZE*'nP' + '2nP')
+        s = size('3nPP' + PySet_MINSIZE*'nP' + '2nP')
         for sample in samples:
             minused = len(sample)
             if minused == 0: tmp = 1