Fix UDP socket FD leak: call close_dispatcher() in worker and discovery cleanup (DataDog#23254)

Author: Kyle-Neale

snmp/datadog_checks/snmp/discovery.py

@@ -53,8 +53,9 @@ def discover_instances(config, interval, check_ref):
                     del check
                     continue
                 finally:
-                    # Drain tasks left by this SNMP call; leftover handle_timeout tasks
-                    # would stop the loop before the next host's request completes.
+                    # Close the host's transport dispatcher to release its UDP socket FD, then
+                    # drain any leftover handle_timeout tasks so they don't stop the next host's loop.
+                    host_config._snmp_engine.transport_dispatcher.close_dispatcher()
                     _pending = asyncio.all_tasks(loop)
                     for _t in _pending:
                         _t.cancel()

snmp/datadog_checks/snmp/snmp.py

@@ -496,7 +496,11 @@ def _check_device(self, config, isolated_loop=False):
             return error, tags
         finally:
             if loop is not None:
-                # Cancel pending pysnmp tasks and close the loop to release file descriptors.
+                # Explicitly close the transport dispatcher to release UDP socket FDs.
+                # asyncio.all_tasks only cancels Task objects; the UdpAsyncioTransport is a
+                # DatagramProtocol/Transport pair — its FD is only released by close_dispatcher().
+                config._snmp_engine.transport_dispatcher.close_dispatcher()
+                # Cancel remaining pysnmp tasks (e.g. handle_timeout) and close the loop.
                 pending = asyncio.all_tasks(loop)
                 for task in pending:
                     task.cancel()