[3.12] gh-116143: Fix race condition in pydoc _start_server (GH-116144) (#116415)

gh-116143: Fix race condition in pydoc _start_server (GH-116144)
(cherry picked from commit 02ee475)

Co-authored-by: Itamar Oren <[email protected]>

Author: miss-islington

Lib/pydoc.py

@@ -2493,6 +2493,7 @@ def __init__(self, urlhandler, host, port):
             threading.Thread.__init__(self)
             self.serving = False
             self.error = None
+            self.docserver = None
 
         def run(self):
             """Start the server."""
@@ -2525,9 +2526,9 @@ def stop(self):
 
     thread = ServerThread(urlhandler, hostname, port)
     thread.start()
-    # Wait until thread.serving is True to make sure we are
-    # really up before returning.
-    while not thread.error and not thread.serving:
+    # Wait until thread.serving is True and thread.docserver is set
+    # to make sure we are really up before returning.
+    while not thread.error and not (thread.serving and thread.docserver):
         time.sleep(.01)
     return thread
 

Misc/NEWS.d/next/Library/2024-03-05-20-53-34.gh-issue-116143.sww6Zl.rst

@@ -0,0 +1,3 @@
+Fix a race in pydoc ``_start_server``, eliminating a window in which
+``_start_server`` can return a thread that is "serving" but without a
+``docserver`` set.