Update PEP 338 to reflect changes to run_module implementation (import lock is now held only when really needed)

pep-0338.txt

@@ -170,10 +170,9 @@ The delegation has the form::
     If the argument ``alter_sys`` is supplied and evaluates to ``True``,
     then ``sys.argv[0]`` is updated with the value of ``__file__``
     and ``sys.modules[__name__]`` is updated with a temporary module
-    object for the module being executed. The import lock is used to
-    prevent other threads from seeing the partially initialised module
-    object. Both ``sys.argv[0]`` and ``sys.modules[__name__]`` are
-    restored to their original values before this function returns.
+    object for the module being executed. Both ``sys.argv[0]`` and
+    ``sys.modules[__name__]`` are restored to their original values
+    before this function returns.
 
 When invoked as a script, the ``runpy`` module finds and executes the
 module supplied as the first argument.  It adjusts ``sys.argv`` by
@@ -203,8 +202,9 @@ the ``runpy`` module. These are listed below.
   This may result in ``sys.argv[0]`` being set to ``None`` if file
   name information is not available.
 
-- The import lock is used to avoid potential threading issues that arise
-  when alter_sys is set to True.
+- The import lock is NOT used to avoid potential threading issues that
+  arise when alter_sys is set to True. Instead, it is recommended that
+  threaded code simply avoid using this flag.
 
 Alternatives
 ============
@@ -232,6 +232,14 @@ single ``run_module()`` function needed to implement the updates to
 the ``-m`` switch. In the interests of simplicity, those extra functions
 have been dropped from the proposed API.
 
+After the original implementation in SVN, it became clear that holding
+the import lock when executing the initial application script was not
+correct (e.g. ``python -m test.regrtest test_threadedimport`` failed).
+So the ``run_module`` function only holds the import lock during the
+actual search for the module, and releases it before execution, even if
+``alter_sys`` is set.
+
+
 
 References
 ==========