Issue #12856: Ensure child processes do not inherit the parent's random seed for filename generation in the tempfile module.

Patch by Brian Harring.

Lib/tempfile.py

@@ -118,9 +118,16 @@ class _RandomNameSequence:
 
     def __init__(self):
         self.mutex = _allocate_lock()
-        self.rng = _Random()
         self.normcase = _os.path.normcase
 
+    @property
+    def rng(self):
+        cur_pid = _os.getpid()
+        if cur_pid != getattr(self, '_rng_pid', None):
+            self._rng = _Random()
+            self._rng_pid = cur_pid
+        return self._rng
+
     def __iter__(self):
         return self