Add docs for WSGIDestroyInterpreter directive.

docs/configuration-directives/WSGIDestroyInterpreter.rst

@@ -0,0 +1,25 @@
+======================
+WSGIDestroyInterpreter
+======================
+
+:Description: Enable/disable cleanup of Python interpreter.
+:Syntax: ``WSGIDestroyInterpreter On|Off``
+:Default: ``WSGIDestroyInterpreter On``
+:Context: server config
+
+The ``WSGIDestroyInterpreter`` directive is used to control whether the Python
+interpreter is destroyed when processes are shutdown or restarted. By default
+the Python interpreter is destroyed when the process is shutdown or restarted.
+
+This directive was added due to changes in Python 3.9 where the Python cleanup
+behaviour was changed such that it would wait on daemon threads to complete.
+This could cause cleanup of the Python interpreter to hang in the some cases
+where threads were created external to Python, as is the case where Python is
+embedded in a C program such as mod_wsgi with Apache.
+
+This problem of hanging when cleanup of the Python interpreter was attempted
+was especially noticeable when using mod_wsgi to host Trac.
+
+Note that it is not known whether versions of Python newer than 3.9 still have
+this problem or whether further changes were made in Python interpreter cleanup
+code.

docs/configuration.rst

@@ -14,6 +14,7 @@ Configuration
    configuration-directives/WSGICaseSensitivity
    configuration-directives/WSGIChunkedRequest
    configuration-directives/WSGIDaemonProcess
+   configuration-directives/WSGIDestroyInterpreter
    configuration-directives/WSGIImportScript
    configuration-directives/WSGILazyInitialization
    configuration-directives/WSGIPassAuthorization