""" Message stream types and APIs. """ import inspect from contextlib import contextmanager, asynccontextmanager from dataclasses import dataclass from typing import ( Any, Iterator, Optional, Callable, AsyncGenerator, ) import warnings import trio from ._ipc import Channel from ._exceptions import unpack_error from ._state import current_actor from .log import get_logger log = get_logger(__name__) # TODO: generic typing like trio's receive channel # but with msgspec messages? # class ReceiveChannel(AsyncResource, Generic[ReceiveType]): class ReceiveMsgStream(trio.abc.ReceiveChannel): """A wrapper around a ``trio._channel.MemoryReceiveChannel`` with special behaviour for signalling stream termination across an inter-actor ``Channel``. This is the type returned to a local task which invoked a remote streaming function using `Portal.run()`. Termination rules: - if the local task signals stop iteration a cancel signal is relayed to the remote task indicating to stop streaming - if the remote task signals the end of a stream, raise a ``StopAsyncIteration`` to terminate the local ``async for`` """ def __init__( self, ctx: 'Context', # typing: ignore # noqa rx_chan: trio.abc.ReceiveChannel, shield: bool = False, ) -> None: self._ctx = ctx self._rx_chan = rx_chan self._shielded = shield # flag to denote end of stream self._eoc: bool = False # delegate directly to underlying mem channel def receive_nowait(self): msg = self._rx_chan.receive_nowait() return msg['yield'] async def receive(self): # see ``.aclose()`` for an alt to always checking this if self._eoc: raise trio.EndOfChannel try: msg = await self._rx_chan.receive() return msg['yield'] except KeyError: # internal error should never get here assert msg.get('cid'), ("Received internal error at portal?") # TODO: handle 2 cases with 3.10 match syntax # - 'stop' # - 'error' # possibly just handle msg['stop'] here! if msg.get('stop'): log.debug(f"{self} was stopped at remote end") # when the send is closed we assume the stream has # terminated and signal this local iterator to stop await self.aclose() # XXX: this causes ``ReceiveChannel.__anext__()`` to # raise a ``StopAsyncIteration``. raise trio.EndOfChannel # TODO: test that shows stream raising an expected error!!! elif msg.get('error'): # raise the error message raise unpack_error(msg, self._ctx.chan) else: raise except trio.ClosedResourceError: # XXX: this indicates that a `stop` message was # sent by the far side of the underlying channel. # Currently this is triggered by calling ``.aclose()`` on # the send side of the channel inside # ``Actor._push_result()``, but maybe it should be put here? # to avoid exposing the internal mem chan closing mechanism? # in theory we could instead do some flushing of the channel # if needed to ensure all consumers are complete before # triggering closure too early? # Locally, we want to close this stream gracefully, by # terminating any local consumers tasks deterministically. # We **don't** want to be closing this send channel and not # relaying a final value to remaining consumers who may not # have been scheduled to receive it yet? # lots of testing to do here # when the send is closed we assume the stream has # terminated and signal this local iterator to stop await self.aclose() raise # propagate except trio.Cancelled: # relay cancels to the remote task await self.aclose() raise @contextmanager def shield( self ) -> Iterator['ReceiveMsgStream']: # noqa """Shield this stream's underlying channel such that a local consumer task can be cancelled (and possibly restarted) using ``trio.Cancelled``. Note that here, "shielding" here guards against relaying a ``'stop'`` message to the far end of the stream thus keeping the stream machinery active and ready for further use, it does not have anything to do with an internal ``trio.CancelScope``. """ self._shielded = True yield self self._shielded = False async def aclose(self): """Cancel associated remote actor task and local memory channel on close. """ self._eoc = True # XXX: keep proper adherance to trio's `.aclose()` semantics: # https://trio.readthedocs.io/en/stable/reference-io.html#trio.abc.AsyncResource.aclose rx_chan = self._rx_chan if rx_chan._closed: log.warning(f"{self} is already closed") # this stream has already been closed so silently succeed as # per ``trio.AsyncResource`` semantics. # https://trio.readthedocs.io/en/stable/reference-io.html#trio.abc.AsyncResource.aclose return # TODO: broadcasting to multiple consumers # stats = rx_chan.statistics() # if stats.open_receive_channels > 1: # # if we've been cloned don't kill the stream # log.debug( # "there are still consumers running keeping stream alive") # return if self._shielded: log.warning(f"{self} is shielded, portal channel being kept alive") return # NOTE: this is super subtle IPC messaging stuff: # Relay stop iteration to far end **iff** we're # in bidirectional mode. If we're only streaming # *from* one side then that side **won't** have an # entry in `Actor._cids2qs` (maybe it should though?). # So any `yield` or `stop` msgs sent from the caller side # will cause key errors on the callee side since there is # no entry for a local feeder mem chan since the callee task # isn't expecting messages to be sent by the caller. # Thus, we must check that this context DOES NOT # have a portal reference to ensure this is indeed the callee # side and can relay a 'stop'. In the bidirectional case, # `Context.open_stream()` will create the `Actor._cids2qs` # entry from a call to `Actor.get_memchans()`. if not self._ctx._portal: try: # only for 2 way streams can we can send # stop from the caller side await self._ctx.send_stop() except trio.BrokenResourceError: # the underlying channel may already have been pulled # in which case our stop message is meaningless since # it can't traverse the transport. log.debug(f'Channel for {self} was already closed') # close the local mem chan??!? # NOT if we're a ``MsgStream``! # BECAUSE this same core-msg-loop mem recv-chan is used to deliver # the potential final result from the surrounding inter-actor # `Context` so we don't want to close it until that context has # run to completion. # XXX: Notes on old behaviour. # In the receive-only case, ``Portal.open_stream_from()`` should # call this explicitly on teardown but additionally if for some # reason stream consumer code tries to manually receive a new # value before ``.aclose()`` is called **but** the far end has # stopped `.receive()` **must** raise ``trio.EndofChannel`` in # order to avoid an infinite hang on ``.__anext__()``. So we can # instead uncomment this check and close the underlying msg-loop # mem chan below and not then **not** check for ``self._eoc`` in # ``.receive()`` (if for some reason we think that check is # a bottle neck - not likely) such that the # ``trio.ClosedResourceError`` would instead trigger the # ``trio.EndOfChannel`` in ``.receive()`` (as it originally was # before bi-dir streaming support). # if not isinstance(self, MsgStream): # await rx_chan.aclose() # TODO: but make it broadcasting to consumers # def clone(self): # """Clone this receive channel allowing for multi-task # consumption from the same channel. # """ # return ReceiveStream( # self._cid, # self._rx_chan.clone(), # self._portal, # ) class MsgStream(ReceiveMsgStream, trio.abc.Channel): """ Bidirectional message stream for use within an inter-actor actor ``Context```. """ async def send( self, data: Any ) -> None: await self._ctx.chan.send({'yield': data, 'cid': self._ctx.cid}) @dataclass class Context: '''An inter-actor task communication context. Allows maintaining task or protocol specific state between 2 communicating actor tasks. A unique context is created on the callee side/end for every request to a remote actor from a portal. A context can be cancelled and (possibly eventually restarted) from either side of the underlying IPC channel. A context can be used to open task oriented message streams and can be thought of as an IPC aware inter-actor cancel scope. ''' chan: Channel cid: str # only set on the caller side _portal: Optional['Portal'] = None # type: ignore # noqa _recv_chan: Optional[trio.MemoryReceiveChannel] = None _result: Optional[Any] = False _cancel_called: bool = False # only set on the callee side _cancel_scope: Optional[trio.CancelScope] = None async def send_yield(self, data: Any) -> None: warnings.warn( "`Context.send_yield()` is now deprecated. " "Use ``MessageStream.send()``. ", DeprecationWarning, stacklevel=2, ) await self.chan.send({'yield': data, 'cid': self.cid}) async def send_stop(self) -> None: await self.chan.send({'stop': True, 'cid': self.cid}) async def cancel(self) -> None: '''Cancel this inter-actor-task context. Request that the far side cancel it's current linked context, Timeout quickly in an attempt to sidestep 2-generals... ''' self._cancel_called = True if self._portal: # caller side: if not self._portal: raise RuntimeError( "No portal found, this is likely a callee side context" ) cid = self.cid with trio.move_on_after(0.5) as cs: cs.shield = True log.warning( f"Cancelling stream {cid} to " f"{self._portal.channel.uid}") # NOTE: we're telling the far end actor to cancel a task # corresponding to *this actor*. The far end local channel # instance is passed to `Actor._cancel_task()` implicitly. await self._portal.run_from_ns('self', '_cancel_task', cid=cid) if cs.cancelled_caught: # XXX: there's no way to know if the remote task was indeed # cancelled in the case where the connection is broken or # some other network error occurred. # if not self._portal.channel.connected(): if not self.chan.connected(): log.warning( "May have failed to cancel remote task " f"{cid} for {self._portal.channel.uid}") else: # ensure callee side assert self._cancel_scope # TODO: should we have an explicit cancel message # or is relaying the local `trio.Cancelled` as an # {'error': trio.Cancelled, cid: "blah"} enough? # This probably gets into the discussion in # https://github.com/goodboy/tractor/issues/36 self._cancel_scope.cancel() @asynccontextmanager async def open_stream( self, shield: bool = False, ) -> AsyncGenerator[MsgStream, None]: '''Open a ``MsgStream``, a bi-directional stream connected to the cross-actor (far end) task for this ``Context``. This context manager must be entered on both the caller and callee for the stream to logically be considered "connected". A ``MsgStream`` is currently "one-shot" use, meaning if you close it you can not "re-open" it for streaming and instead you must re-establish a new surrounding ``Context`` using ``Portal.open_context()``. In the future this may change but currently there seems to be no obvious reason to support "re-opening": - pausing a stream can be done with a message. - task errors will normally require a restart of the entire scope of the inter-actor task context due to the nature of ``trio``'s cancellation system. ''' actor = current_actor() # here we create a mem chan that corresponds to the # far end caller / callee. # NOTE: in one way streaming this only happens on the # caller side inside `Actor.send_cmd()` so if you try # to send a stop from the caller to the callee in the # single-direction-stream case you'll get a lookup error # currently. _, recv_chan = actor.get_memchans( self.chan.uid, self.cid ) # XXX: If the underlying receive mem chan has been closed then # likely client code has already exited a ``.open_stream()`` # block prior. we error here until such a time that we decide # allowing streams to be "re-connected" is supported and/or # a good idea. if recv_chan._closed: task = trio.lowlevel.current_task().name raise trio.ClosedResourceError( f'stream for {actor.uid[0]}:{task} has already been closed.' '\nRe-opening a closed stream is not yet supported!' '\nConsider re-calling the containing `@tractor.context` func' ) async with MsgStream( ctx=self, rx_chan=recv_chan, shield=shield, ) as rchan: if self._portal: self._portal._streams.add(rchan) try: # ensure we aren't cancelled before delivering # the stream # await trio.lowlevel.checkpoint() yield rchan except trio.EndOfChannel: # stream iteration stop signal raise else: # XXX: Make the stream "one-shot use". On exit, signal # ``trio.EndOfChannel``/``StopAsyncIteration`` to the # far end. await self.send_stop() finally: if self._portal: self._portal._streams.remove(rchan) async def result(self) -> Any: '''From a caller side, wait for and return the final result from the callee side task. ''' assert self._portal, "Context.result() can not be called from callee!" assert self._recv_chan if self._result is False: if not self._recv_chan._closed: # type: ignore # wait for a final context result consuming # and discarding any bi dir stream msgs still # in transit from the far end. while True: msg = await self._recv_chan.receive() try: self._result = msg['return'] break except KeyError: if 'yield' in msg: # far end task is still streaming to us.. log.warning(f'Remote stream deliverd {msg}') # do disard continue elif 'stop' in msg: log.debug('Remote stream terminated') continue # internal error should never get here assert msg.get('cid'), ( "Received internal error at portal?") raise unpack_error(msg, self._portal.channel) return self._result async def started(self, value: Optional[Any] = None) -> None: if self._portal: raise RuntimeError( f"Caller side context {self} can not call started!") await self.chan.send({'started': value, 'cid': self.cid}) # TODO: do we need a restart api? # async def restart(self) -> None: # pass def stream(func: Callable) -> Callable: """Mark an async function as a streaming routine with ``@stream``. """ # annotate # TODO: apply whatever solution ``mypy`` ends up picking for this: # https://github.com/python/mypy/issues/2087#issuecomment-769266912 func._tractor_stream_function = True # type: ignore sig = inspect.signature(func) params = sig.parameters if 'stream' not in params and 'ctx' in params: warnings.warn( "`@tractor.stream decorated funcs should now declare a `stream` " " arg, `ctx` is now designated for use with @tractor.context", DeprecationWarning, stacklevel=2, ) if ( 'ctx' not in params and 'to_trio' not in params and 'stream' not in params ): raise TypeError( "The first argument to the stream function " f"{func.__name__} must be `ctx: tractor.Context` " "(Or ``to_trio`` if using ``asyncio`` in guest mode)." ) return func def context(func: Callable) -> Callable: """Mark an async function as a streaming routine with ``@context``. """ # annotate # TODO: apply whatever solution ``mypy`` ends up picking for this: # https://github.com/python/mypy/issues/2087#issuecomment-769266912 func._tractor_context_function = True # type: ignore sig = inspect.signature(func) params = sig.parameters if 'ctx' not in params: raise TypeError( "The first argument to the context function " f"{func.__name__} must be `ctx: tractor.Context`" ) return func