Revert "bpo-37193: remove thread objects which finished process its request (GH-13893)" (GH-23107)

This reverts commit c415590212.

Lib/socketserver.py

@@ -128,7 +128,6 @@ import selectors
 import os
 import sys
 import threading
-import contextlib
 from io import BufferedIOBase
 from time import monotonic as time
 
@@ -629,55 +628,6 @@ if hasattr(os, "fork"):
             self.collect_children(blocking=self.block_on_close)
 
 
-class _Threads(list):
-    """
-    Joinable list of all non-daemon threads.
-    """
-    def __init__(self):
-        self._lock = threading.Lock()
-
-    def append(self, thread):
-        if thread.daemon:
-            return
-        with self._lock:
-            super().append(thread)
-
-    def remove(self, thread):
-        with self._lock:
-            # should not happen, but safe to ignore
-            with contextlib.suppress(ValueError):
-                super().remove(thread)
-
-    def remove_current(self):
-        """Remove a current non-daemon thread."""
-        thread = threading.current_thread()
-        if not thread.daemon:
-            self.remove(thread)
-
-    def pop_all(self):
-        with self._lock:
-            self[:], result = [], self[:]
-        return result
-
-    def join(self):
-        for thread in self.pop_all():
-            thread.join()
-
-
-class _NoThreads:
-    """
-    Degenerate version of _Threads.
-    """
-    def append(self, thread):
-        pass
-
-    def join(self):
-        pass
-
-    def remove_current(self):
-        pass
-
-
 class ThreadingMixIn:
     """Mix-in class to handle each request in a new thread."""
 
@@ -686,9 +636,9 @@ class ThreadingMixIn:
     daemon_threads = False
     # If true, server_close() waits until all non-daemonic threads terminate.
     block_on_close = True
-    # Threads object
+    # For non-daemonic threads, list of threading.Threading objects
     # used by server_close() to wait for all threads completion.
-    _threads = _NoThreads()
+    _threads = None
 
     def process_request_thread(self, request, client_address):
         """Same as in BaseServer but as a thread.
@@ -701,24 +651,27 @@ class ThreadingMixIn:
         except Exception:
             self.handle_error(request, client_address)
         finally:
-            try:
-                self.shutdown_request(request)
-            finally:
-                self._threads.remove_current()
+            self.shutdown_request(request)
 
     def process_request(self, request, client_address):
         """Start a new thread to process the request."""
-        if self.block_on_close:
-            vars(self).setdefault('_threads', _Threads())
         t = threading.Thread(target = self.process_request_thread,
                              args = (request, client_address))
         t.daemon = self.daemon_threads
-        self._threads.append(t)
+        if not t.daemon and self.block_on_close:
+            if self._threads is None:
+                self._threads = []
+            self._threads.append(t)
         t.start()
 
     def server_close(self):
         super().server_close()
-        self._threads.join()
+        if self.block_on_close:
+            threads = self._threads
+            self._threads = None
+            if threads:
+                for thread in threads:
+                    thread.join()
 
 
 if hasattr(os, "fork"):