stdpy: threading2: join non-daemonic threads at interpreter shutdown

Fixes #758

direct/src/stdpy/threading2.py

@@ -14,6 +14,7 @@ module, and so it is therefore layered on top of Panda's thread
 implementation. """
 
 import sys as _sys
+import atexit as _atexit
 
 from direct.stdpy import thread as _thread
 from direct.stdpy.thread import stack_size, _newname, _local as local
@@ -395,6 +396,10 @@ class Thread(_Verbose):
     # operation on/with a NoneType
     __exc_info = _sys.exc_info
 
+    # Set to True when the _shutdown handler is registered as atexit function.
+    # Protected by _active_limbo_lock.
+    __registered_atexit = False
+
     def __init__(self, group=None, target=None, name=None,
                  args=(), kwargs=None, verbose=None, daemon=None):
         assert group is None, "group argument must be None for now"
@@ -439,6 +444,14 @@ class Thread(_Verbose):
             self._note("%s.start(): starting thread", self)
         _active_limbo_lock.acquire()
         _limbo[self] = self
+
+        # If we are starting a non-daemon thread, we need to call join() on it
+        # when the interpreter exits.  Python will call _shutdown() on the
+        # built-in threading module automatically, but not on our module.
+        if not self.__daemonic and not Thread.__registered_atexit:
+            _atexit.register(_shutdown)
+            Thread.__registered_atexit = True
+
         _active_limbo_lock.release()
         _start_new_thread(self.__bootstrap, ())
         self.__started = True