pythongh-113538: Allow client connections to be closed

Give applications the option of more forcefully terminating client
connections for asyncio servers. Useful when terminating a service and
there is limited time to wait for clients to finish up their work.

Author: CendioOssman

Doc/library/asyncio-eventloop.rst

@@ -1641,6 +1641,23 @@ Do not instantiate the :class:`Server` class directly.
       coroutine to wait until the server is closed (and no more
       connections are active).
 
+   .. method:: close_clients()
+
+      Close all existing incoming client connections.
+
+      Calls :meth:`Transport.close` on all associated transports.
+
+      .. versionadded:: 3.13
+
+   .. method:: abort_clients()
+
+      Close all existing incoming client connections immediately,
+      without waiting for pending operations to complete.
+
+      Calls :meth:`Transport.abort` on all associated transports.
+
+      .. versionadded:: 3.13
+
    .. method:: get_loop()
 
       Return the event loop associated with the server object.

Doc/whatsnew/3.13.rst

@@ -168,6 +168,10 @@ asyncio
   the Unix socket when the server is closed.
   (Contributed by Pierre Ossman in :gh:`111246`.)
 
+* Add :meth:`asyncio.Server.close_clients` and
+  :meth:`asyncio.Server.abort_clients` methods which allows to more
+  forcefully close an asyncio server.
+
 copy
 ----
 

Lib/asyncio/base_events.py

@@ -277,7 +277,7 @@ def __init__(self, loop, sockets, protocol_factory, ssl_context, backlog,
                  ssl_handshake_timeout, ssl_shutdown_timeout=None):
         self._loop = loop
         self._sockets = sockets
-        self._active_count = 0
+        self._clients = set()
         self._waiters = []
         self._protocol_factory = protocol_factory
         self._backlog = backlog
@@ -290,14 +290,14 @@ def __init__(self, loop, sockets, protocol_factory, ssl_context, backlog,
     def __repr__(self):
         return f'<{self.__class__.__name__} sockets={self.sockets!r}>'
 
-    def _attach(self):
+    def _attach(self, transport):
         assert self._sockets is not None
-        self._active_count += 1
+        self._clients.add(transport)
 
-    def _detach(self):
-        assert self._active_count > 0
-        self._active_count -= 1
-        if self._active_count == 0 and self._sockets is None:
+    def _detach(self, transport):
+        assert transport in self._clients
+        self._clients.remove(transport)
+        if len(self._clients) == 0 and self._sockets is None:
             self._wakeup()
 
     def _wakeup(self):
@@ -346,9 +346,17 @@ def close(self):
             self._serving_forever_fut.cancel()
             self._serving_forever_fut = None
 
-        if self._active_count == 0:
+        if len(self._clients) == 0:
             self._wakeup()
 
+    def close_clients(self):
+        for transport in self._clients.copy():
+            transport.close()
+
+    def abort_clients(self):
+        for transport in self._clients.copy():
+            transport.abort()
+
     async def start_serving(self):
         self._start_serving()
         # Skip one loop iteration so that all 'loop.add_reader'

Lib/asyncio/events.py

@@ -173,6 +173,14 @@ def close(self):
         """Stop serving.  This leaves existing connections open."""
         raise NotImplementedError
 
+    def close_clients(self):
+        """Close all active connections."""
+        raise NotImplementedError
+
+    def abort_clients(self):
+        """Close all active connections immediately."""
+        raise NotImplementedError
+
     def get_loop(self):
         """Get the event loop the Server object is attached to."""
         raise NotImplementedError

Lib/asyncio/proactor_events.py

@@ -63,7 +63,7 @@ def __init__(self, loop, sock, protocol, waiter=None,
         self._called_connection_lost = False
         self._eof_written = False
         if self._server is not None:
-            self._server._attach()
+            self._server._attach(self)
         self._loop.call_soon(self._protocol.connection_made, self)
         if waiter is not None:
             # only wake up the waiter when connection_made() has been called
@@ -167,7 +167,7 @@ def _call_connection_lost(self, exc):
             self._sock = None
             server = self._server
             if server is not None:
-                server._detach()
+                server._detach(self)
                 self._server = None
             self._called_connection_lost = True
 

Lib/asyncio/selector_events.py

@@ -787,7 +787,7 @@ def __init__(self, loop, sock, protocol, extra=None, server=None):
         self._paused = False  # Set when pause_reading() called
 
         if self._server is not None:
-            self._server._attach()
+            self._server._attach(self)
         loop._transports[self._sock_fd] = self
 
     def __repr__(self):
@@ -902,7 +902,7 @@ def _call_connection_lost(self, exc):
             self._loop = None
             server = self._server
             if server is not None:
-                server._detach()
+                server._detach(self)
                 self._server = None
 
     def get_write_buffer_size(self):

Lib/test/test_asyncio/test_server.py

@@ -187,7 +187,65 @@ async def serve(rd, wr):
         loop.call_soon(wr.close)
         await srv.wait_closed()
 
+    async def test_close_clients(self):
+        async def serve(rd, wr):
+            try:
+                await rd.read()
+            finally:
+                wr.close()
+                await wr.wait_closed()
+
+        srv = await asyncio.start_server(serve, socket_helper.HOSTv4, 0)
+        self.addCleanup(srv.close)
+
+        addr = srv.sockets[0].getsockname()
+        (rd, wr) = await asyncio.open_connection(addr[0], addr[1])
+        self.addCleanup(wr.close)
+
+        task = asyncio.create_task(srv.wait_closed())
+        await asyncio.sleep(0)
+        self.assertFalse(task.done())
 
+        srv.close()
+        srv.close_clients()
+        await asyncio.sleep(0.1) # FIXME: flush call_soon()?
+        self.assertTrue(task.done())
+
+    async def test_abort_clients(self):
+        async def serve(rd, wr):
+            nonlocal s_rd, s_wr
+            s_rd = rd
+            s_wr = wr
+            await wr.wait_closed()
+
+        s_rd = s_wr = None
+        srv = await asyncio.start_server(serve, socket_helper.HOSTv4, 0)
+        self.addCleanup(srv.close)
+
+        addr = srv.sockets[0].getsockname()
+        (c_rd, c_wr) = await asyncio.open_connection(addr[0], addr[1])
+        self.addCleanup(c_wr.close)
+
+        # Make sure both sides are in a paused state
+        while (s_wr.transport.get_write_buffer_size() == 0 or
+               c_wr.transport.is_reading()):
+            while s_wr.transport.get_write_buffer_size() == 0:
+                s_wr.write(b'a' * 65536)
+                await asyncio.sleep(0)
+            await asyncio.sleep(0.1) # FIXME: More socket buffer space magically appears?
+
+        task = asyncio.create_task(srv.wait_closed())
+        await asyncio.sleep(0)
+        self.assertFalse(task.done())
+
+        # Sanity check
+        self.assertNotEqual(s_wr.transport.get_write_buffer_size(), 0)
+        self.assertFalse(c_wr.transport.is_reading())
+
+        srv.close()
+        srv.abort_clients()
+        await asyncio.sleep(0.1) # FIXME: flush call_soon()?
+        self.assertTrue(task.done())
 
 
 # Test the various corner cases of Unix server socket removal

Misc/NEWS.d/next/Library/2024-01-22-15-50-58.gh-issue-113538.v2wrwg.rst

@@ -0,0 +1,3 @@
+Add :meth:`asyncio.Server.close_clients` and
+:meth:`asyncio.Server.abort_clients` methods which allows to more forcefully
+close an asyncio server.