When forking multiple processes, properly initialize the random seed

Avoid seeding the random module with the same value in all processes.
If available, use the same method used by random.py, otherwise
generate a seed using the current time in milliseconds and the pid.

diff --git a/tornado/httpserver.py b/tornado/httpserver.py
index be52c9de9087cdc1181bba35e62525523d08302a..b85704b44e3ffdadbf413606fc322493f80b4b6b 100644 (file)
--- a/tornado/httpserver.py
+++ b/tornado/httpserver.py
@@ -203,6 +203,17 @@ class HTTPServer(object):
             logging.info("Pre-forking %d server processes", num_processes)
             for i in range(num_processes):
                 if os.fork() == 0:
+                    import random
+                    from binascii import hexlify
+                    try:
+                        # If available, use the same method as
+                        # random.py
+                        seed = long(hexlify(os.urandom(16)), 16)
+                    except NotImplementedError:
+                        # Include the pid to avoid initializing two
+                        # processes to the same value
+                        seed(int(time.time() * 1000) ^ os.getpid())
+                    random.seed(seed)
                     self.io_loop = ioloop.IOLoop.instance()
                     self.io_loop.add_handler(
                         self._socket.fileno(), self._handle_events,