On Fri, Jul 30, 2021 at 4:19 PM G S Niteesh Babu <niteesh...@gmail.com>
wrote:
> Instead of manually connecting and disconnecting from the
> server. We now rely on the runstate to manage the QMP
> connection.
>
> Along with this the ability to reconnect on certain exceptions
> has also been added.
>
> Signed-off-by: G S Niteesh Babu <niteesh...@gmail.com>
> ---
> python/qemu/aqmp/aqmp_tui.py | 109 ++++++++++++++++++++++++++++++-----
> 1 file changed, 94 insertions(+), 15 deletions(-)
>
> diff --git a/python/qemu/aqmp/aqmp_tui.py b/python/qemu/aqmp/aqmp_tui.py
> index 0d5ec62cb7..ef91883fa5 100644
> --- a/python/qemu/aqmp/aqmp_tui.py
> +++ b/python/qemu/aqmp/aqmp_tui.py
> @@ -25,8 +25,9 @@
> import urwid_readline
>
> from ..qmp import QEMUMonitorProtocol, QMPBadPortError
> +from .error import ProtocolError
> from .message import DeserializationError, Message, UnexpectedTypeError
> -from .protocol import ConnectError
> +from .protocol import ConnectError, Runstate
> from .qmp_client import ExecInterruptedError, QMPClient
> from .util import create_task, pretty_traceback
>
> @@ -67,12 +68,24 @@ def format_json(msg: str) -> str:
> return ' '.join(words)
>
>
> +def type_name(mtype: Any) -> str:
> + """
> + Returns the type name
> + """
> + return type(mtype).__name__
>
This is a lot of lines for something that doesn't do very much -- do we
really need it?
> +
> +
> class App(QMPClient):
> - def __init__(self, address: Union[str, Tuple[str, int]]) -> None:
> + def __init__(self, address: Union[str, Tuple[str, int]], num_retries:
> int,
> + retry_delay: Optional[int]) -> None:
> urwid.register_signal(type(self), UPDATE_MSG)
> self.window = Window(self)
> self.address = address
> self.aloop: Optional[Any] = None # FIXME: Use more concrete type.
> + self.num_retries = num_retries
> + self.retry_delay = retry_delay
> + self.retry: bool = False
> + self.disconnecting: bool = False
>
Why is this one needed again ? ...
> super().__init__()
>
> def add_to_history(self, msg: str, level: Optional[str] = None) ->
> None:
> @@ -119,7 +132,7 @@ def _cb_inbound(self, msg: Message) -> Message:
> LOGGER.info('Error server disconnected before reply')
> urwid.emit_signal(self, UPDATE_MSG,
> '{"error": "Server disconnected before
> reply"}')
> - self._set_status("Server disconnected")
> + await self.disconnect()
> except Exception as err:
> LOGGER.error('Exception from _send_to_server: %s', str(err))
> raise err
> @@ -136,15 +149,29 @@ def kill_app(self) -> None:
> create_task(self._kill_app())
>
> async def _kill_app(self) -> None:
> - # It is ok to call disconnect even in disconnect state
> + await self.disconnect()
> + LOGGER.debug('Disconnect finished. Exiting app')
> + raise urwid.ExitMainLoop()
> +
> + async def disconnect(self) -> None:
> + if self.disconnecting:
> + return
> try:
> - await self.disconnect()
> - LOGGER.debug('Disconnect finished. Exiting app')
> + self.disconnecting = True
> + await super().disconnect()
> + self.retry = True
> + except EOFError as err:
> + LOGGER.info('disconnect: %s', type_name(err))
> + self.retry = True
> + except ProtocolError as err:
> + LOGGER.info('disconnect: %s', type_name(err))
> + self.retry = False
> except Exception as err:
> - LOGGER.info('_kill_app: %s', str(err))
> - # Let the app crash after providing a proper stack trace
> + LOGGER.error('disconnect: Unhandled exception %s', str(err))
> + self.retry = False
> raise err
> - raise urwid.ExitMainLoop()
> + finally:
> + self.disconnecting = False
>
> def handle_event(self, event: Message) -> None:
> # FIXME: Consider all states present in qapi/run-state.json
> @@ -161,14 +188,61 @@ def _get_formatted_address(self) -> str:
> addr = f'{host}:{port}'
> return addr
>
> - async def connect_server(self) -> None:
> + async def _retry_connection(self) -> Optional[str]:
> + current_retries = 0
> + err = None
> + # Increase in power sequence of 2 if no delay is provided
> + cur_delay = 1
> + inc_delay = 2
> + if self.retry_delay:
> + inc_delay = 1
> + cur_delay = self.retry_delay
> + # initial try
> + await self.connect_server()
> + while self.retry and current_retries < self.num_retries:
> + LOGGER.info('Connection Failed, retrying in %d', cur_delay)
> + status = f'[Retry #{current_retries} ({cur_delay}s)]'
> + self._set_status(status)
> +
> + await asyncio.sleep(cur_delay)
> +
> + err = await self.connect_server()
> + cur_delay *= inc_delay
> + # Cap delay to 5mins
> + cur_delay = min(cur_delay, 5 * 60)
> + current_retries += 1
> + # If all retries failed report the last error
> + LOGGER.info('All retries failed: %s', str(err))
> + return type_name(err)
>
I had suggested something like an exponential backoff, but maybe a constant
delay would be a little cleaner to implement for right now without getting
too fancy over it. If you go with a simpler retry algorithm, do you think
you could clean up the logic in the retry loop here a bit more?
Something like:
for _ in range(num_retries):
try:
whatever_you_have_to_do_to_connect()
return
except ConnectError as err:
LOGGER.info(...etc)
await asyncio.sleep(whatever_the_delay_is)
# ran out of retries here, presumably the connection manager will just go
idle until the user interferes some other way.
In particular, I think passing around the name of the exception is a little
dubious -- we should be logging with the actual Exception we've received.
> +
> + async def manage_connection(self) -> None:
> + while True:
> + if self.runstate == Runstate.IDLE:
> + LOGGER.info('Trying to reconnect')
>
But will this be true upon the very first boot? This message might not be
right.
> + err = await self._retry_connection()
>
This seems named oddly too, since it might be the initial attempt and not
necessarily a reconnection or a retry.
> + # If retry is still true then, we have exhausted all our
> tries.
> + if self.retry:
> + self._set_status(f'Error: {err}')
>
+ else:
> + addr = self._get_formatted_address()
> + self._set_status(f'[Connected {addr}]')
> + elif self.runstate == Runstate.DISCONNECTING:
> + self._set_status('[Disconnected]')
> + await self.disconnect()
> + # check if a retry is needed
>
Is this required? I would have hoped that after calling disconnect that the
state would have again changed to IDLE and you wouldn't need this clause
here.
> + if self.runstate == Runstate.IDLE:
> + continue
> + await self.runstate_changed()
> +
> + async def connect_server(self) -> Optional[str]:
> try:
> await self.connect(self.address)
> - addr = self._get_formatted_address()
> - self._set_status(f'Connected to {addr}')
> + self.retry = False
> except ConnectError as err:
> LOGGER.info('connect_server: ConnectError %s', str(err))
> - self._set_status('Server shutdown')
> + self.retry = True
> + return type_name(err)
> + return None
>
> def run(self, debug: bool = False) -> None:
> screen = urwid.raw_display.Screen()
> @@ -191,7 +265,7 @@ def run(self, debug: bool = False) -> None:
> event_loop=event_loop)
>
> create_task(self.wait_for_events(), self.aloop)
> - create_task(self.connect_server(), self.aloop)
> + create_task(self.manage_connection(), self.aloop)
> try:
> main_loop.run()
> except Exception as err:
> @@ -333,6 +407,11 @@ def main() -> None:
> parser = argparse.ArgumentParser(description='AQMP TUI')
> parser.add_argument('qmp_server', help='Address of the QMP server'
> '< UNIX socket path | TCP addr:port >')
> + parser.add_argument('--num-retries', type=int, default=10,
> + help='Number of times to reconnect before giving
> up')
> + parser.add_argument('--retry-delay', type=int,
> + help='Time(s) to wait before next retry.'
> + 'Default action is to increase delay in powers of
> 2')
> parser.add_argument('--log-file', help='The Log file name')
> parser.add_argument('--log-level', default='WARNING',
> help='Log level
> <CRITICAL|ERROR|WARNING|INFO|DEBUG|>')
> @@ -348,7 +427,7 @@ def main() -> None:
> except QMPBadPortError as err:
> parser.error(str(err))
>
> - app = App(address)
> + app = App(address, args.num_retries, args.retry_delay)
>
> if args.log_file:
> LOGGER.addHandler(logging.FileHandler(args.log_file))
> --
> 2.17.1
>
>
Right idea overall - possibly needs some polish and to be integrated with
an earlier patch to avoid the intermediate FIXMEs.
Thanks,
--js
