diff options
Diffstat (limited to 'python')
| -rw-r--r-- | python/qemu/aqmp/__init__.py | 6 | ||||
| -rw-r--r-- | python/qemu/aqmp/protocol.py | 159 |
2 files changed, 160 insertions, 5 deletions
diff --git a/python/qemu/aqmp/__init__.py b/python/qemu/aqmp/__init__.py index 5c0de72672..88ead4c023 100644 --- a/python/qemu/aqmp/__init__.py +++ b/python/qemu/aqmp/__init__.py @@ -22,12 +22,16 @@ managing QMP events. # the COPYING file in the top-level directory. from .error import AQMPError -from .protocol import ConnectError +from .protocol import ConnectError, Runstate, StateError # The order of these fields impact the Sphinx documentation order. __all__ = ( + # Classes + 'Runstate', + # Exceptions, most generic to most explicit 'AQMPError', + 'StateError', 'ConnectError', ) diff --git a/python/qemu/aqmp/protocol.py b/python/qemu/aqmp/protocol.py index 2a93da791e..19460857bd 100644 --- a/python/qemu/aqmp/protocol.py +++ b/python/qemu/aqmp/protocol.py @@ -12,11 +12,10 @@ class. import asyncio from asyncio import StreamReader, StreamWriter +from enum import Enum +from functools import wraps from ssl import SSLContext -# import exceptions will be removed in a forthcoming commit. -# The problem stems from pylint/flake8 believing that 'Any' -# is unused because of its only use in a string-quoted type. -from typing import ( # pylint: disable=unused-import # noqa +from typing import ( Any, Awaitable, Callable, @@ -26,6 +25,7 @@ from typing import ( # pylint: disable=unused-import # noqa Tuple, TypeVar, Union, + cast, ) from .error import AQMPError @@ -44,6 +44,20 @@ _TaskFN = Callable[[], Awaitable[None]] # aka ``async def func() -> None`` _FutureT = TypeVar('_FutureT', bound=Optional['asyncio.Future[Any]']) +class Runstate(Enum): + """Protocol session runstate.""" + + #: Fully quiesced and disconnected. + IDLE = 0 + #: In the process of connecting or establishing a session. + CONNECTING = 1 + #: Fully connected and active session. + RUNNING = 2 + #: In the process of disconnecting. + #: Runstate may be returned to `IDLE` by calling `disconnect()`. + DISCONNECTING = 3 + + class ConnectError(AQMPError): """ Raised when the initial connection process has failed. @@ -65,6 +79,76 @@ class ConnectError(AQMPError): return f"{self.error_message}: {self.exc!s}" +class StateError(AQMPError): + """ + An API command (connect, execute, etc) was issued at an inappropriate time. + + This error is raised when a command like + :py:meth:`~AsyncProtocol.connect()` is issued at an inappropriate + time. + + :param error_message: Human-readable string describing the state violation. + :param state: The actual `Runstate` seen at the time of the violation. + :param required: The `Runstate` required to process this command. + """ + def __init__(self, error_message: str, + state: Runstate, required: Runstate): + super().__init__(error_message) + self.error_message = error_message + self.state = state + self.required = required + + +F = TypeVar('F', bound=Callable[..., Any]) # pylint: disable=invalid-name + + +# Don't Panic. +def require(required_state: Runstate) -> Callable[[F], F]: + """ + Decorator: protect a method so it can only be run in a certain `Runstate`. + + :param required_state: The `Runstate` required to invoke this method. + :raise StateError: When the required `Runstate` is not met. + """ + def _decorator(func: F) -> F: + # _decorator is the decorator that is built by calling the + # require() decorator factory; e.g.: + # + # @require(Runstate.IDLE) def foo(): ... + # will replace 'foo' with the result of '_decorator(foo)'. + + @wraps(func) + def _wrapper(proto: 'AsyncProtocol[Any]', + *args: Any, **kwargs: Any) -> Any: + # _wrapper is the function that gets executed prior to the + # decorated method. + + name = type(proto).__name__ + + if proto.runstate != required_state: + if proto.runstate == Runstate.CONNECTING: + emsg = f"{name} is currently connecting." + elif proto.runstate == Runstate.DISCONNECTING: + emsg = (f"{name} is disconnecting." + " Call disconnect() to return to IDLE state.") + elif proto.runstate == Runstate.RUNNING: + emsg = f"{name} is already connected and running." + elif proto.runstate == Runstate.IDLE: + emsg = f"{name} is disconnected and idle." + else: + assert False + raise StateError(emsg, proto.runstate, required_state) + # No StateError, so call the wrapped method. + return func(proto, *args, **kwargs) + + # Return the decorated method; + # Transforming Func to Decorated[Func]. + return cast(F, _wrapper) + + # Return the decorator instance from the decorator factory. Phew! + return _decorator + + class AsyncProtocol(Generic[T]): """ AsyncProtocol implements a generic async message-based protocol. @@ -118,7 +202,24 @@ class AsyncProtocol(Generic[T]): #: exit. self._dc_task: Optional[asyncio.Future[None]] = None + self._runstate = Runstate.IDLE + self._runstate_changed: Optional[asyncio.Event] = None + + @property # @upper_half + def runstate(self) -> Runstate: + """The current `Runstate` of the connection.""" + return self._runstate + @upper_half + async def runstate_changed(self) -> Runstate: + """ + Wait for the `runstate` to change, then return that runstate. + """ + await self._runstate_event.wait() + return self.runstate + + @upper_half + @require(Runstate.IDLE) async def connect(self, address: Union[str, Tuple[str, int]], ssl: Optional[SSLContext] = None) -> None: """ @@ -152,6 +253,30 @@ class AsyncProtocol(Generic[T]): # Section: Session machinery # -------------------------- + @property + def _runstate_event(self) -> asyncio.Event: + # asyncio.Event() objects should not be created prior to entrance into + # an event loop, so we can ensure we create it in the correct context. + # Create it on-demand *only* at the behest of an 'async def' method. + if not self._runstate_changed: + self._runstate_changed = asyncio.Event() + return self._runstate_changed + + @upper_half + @bottom_half + def _set_state(self, state: Runstate) -> None: + """ + Change the `Runstate` of the protocol connection. + + Signals the `runstate_changed` event. + """ + if state == self._runstate: + return + + self._runstate = state + self._runstate_event.set() + self._runstate_event.clear() + @upper_half async def _new_session(self, address: Union[str, Tuple[str, int]], @@ -176,6 +301,8 @@ class AsyncProtocol(Generic[T]): protocol-level failure occurs while establishing a new session, the wrapped error may also be an `AQMPError`. """ + assert self.runstate == Runstate.IDLE + try: phase = "connection" await self._establish_connection(address, ssl) @@ -185,6 +312,7 @@ class AsyncProtocol(Generic[T]): except BaseException as err: emsg = f"Failed to establish {phase}" + # Reset from CONNECTING back to IDLE. await self.disconnect() # NB: CancelledError is not a BaseException before Python 3.8 @@ -197,6 +325,8 @@ class AsyncProtocol(Generic[T]): # Raise BaseExceptions un-wrapped, they're more important. raise + assert self.runstate == Runstate.RUNNING + @upper_half async def _establish_connection( self, @@ -211,6 +341,14 @@ class AsyncProtocol(Generic[T]): UNIX socket path or TCP address/port. :param ssl: SSL context to use, if any. """ + assert self.runstate == Runstate.IDLE + self._set_state(Runstate.CONNECTING) + + # Allow runstate watchers to witness 'CONNECTING' state; some + # failures in the streaming layer are synchronous and will not + # otherwise yield. + await asyncio.sleep(0) + await self._do_connect(address, ssl) @upper_half @@ -240,6 +378,8 @@ class AsyncProtocol(Generic[T]): own negotiations here. The Runstate will be RUNNING upon successful conclusion. """ + assert self.runstate == Runstate.CONNECTING + self._outgoing = asyncio.Queue() reader_coro = self._bh_loop_forever(self._bh_recv_message) @@ -253,6 +393,9 @@ class AsyncProtocol(Generic[T]): self._writer_task, ) + self._set_state(Runstate.RUNNING) + await asyncio.sleep(0) # Allow runstate_event to process + @upper_half @bottom_half def _schedule_disconnect(self) -> None: @@ -266,6 +409,7 @@ class AsyncProtocol(Generic[T]): It can be invoked no matter what the `runstate` is. """ if not self._dc_task: + self._set_state(Runstate.DISCONNECTING) self._dc_task = create_task(self._bh_disconnect()) @upper_half @@ -281,6 +425,7 @@ class AsyncProtocol(Generic[T]): :raise Exception: Arbitrary exception re-raised on behalf of the reader/writer. """ + assert self.runstate == Runstate.DISCONNECTING assert self._dc_task aws: List[Awaitable[object]] = [self._dc_task] @@ -295,6 +440,7 @@ class AsyncProtocol(Generic[T]): await all_defined_tasks # Raise Exceptions from the bottom half. finally: self._cleanup() + self._set_state(Runstate.IDLE) @upper_half def _cleanup(self) -> None: @@ -306,6 +452,7 @@ class AsyncProtocol(Generic[T]): assert (task is None) or task.done() return None if (task and task.done()) else task + assert self.runstate == Runstate.DISCONNECTING self._dc_task = _paranoid_task_erase(self._dc_task) self._reader_task = _paranoid_task_erase(self._reader_task) self._writer_task = _paranoid_task_erase(self._writer_task) @@ -314,6 +461,9 @@ class AsyncProtocol(Generic[T]): self._reader = None self._writer = None + # NB: _runstate_changed cannot be cleared because we still need it to + # send the final runstate changed event ...! + # ---------------------------- # Section: Bottom Half methods # ---------------------------- @@ -328,6 +478,7 @@ class AsyncProtocol(Generic[T]): it is free to wait on any pending actions that may still need to occur in either the reader or writer tasks. """ + assert self.runstate == Runstate.DISCONNECTING def _done(task: Optional['asyncio.Future[Any]']) -> bool: return task is not None and task.done() |