forked from goodboy/tractor
268 lines
9.8 KiB
Python
268 lines
9.8 KiB
Python
"""
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Messaging pattern APIs and helpers.
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"""
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import inspect
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import typing
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from typing import Dict, Any, Set, Union, Callable
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from functools import partial
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from async_generator import aclosing
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import trio
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import wrapt
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from .log import get_logger
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from . import current_actor
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from ._streaming import Context
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__all__ = ['pub']
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log = get_logger('messaging')
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async def fan_out_to_ctxs(
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pub_async_gen_func: typing.Callable, # it's an async gen ... gd mypy
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topics2ctxs: Dict[str, set],
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packetizer: typing.Callable = None,
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) -> None:
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"""Request and fan out quotes to each subscribed actor channel.
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"""
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def get_topics():
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return tuple(topics2ctxs.keys())
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agen = pub_async_gen_func(get_topics=get_topics)
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async with aclosing(agen) as pub_gen:
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async for published in pub_gen:
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ctx_payloads: Dict[str, Any] = {}
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for topic, data in published.items():
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log.debug(f"publishing {topic, data}")
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# build a new dict packet or invoke provided packetizer
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if packetizer is None:
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packet = {topic: data}
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else:
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packet = packetizer(topic, data)
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for ctx in topics2ctxs.get(topic, set()):
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ctx_payloads.setdefault(ctx, {}).update(packet),
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if not ctx_payloads:
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log.debug(f"Unconsumed values:\n{published}")
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# deliver to each subscriber (fan out)
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if ctx_payloads:
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for ctx, payload in ctx_payloads.items():
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try:
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await ctx.send_yield(payload)
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except (
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# That's right, anything you can think of...
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trio.ClosedResourceError, ConnectionResetError,
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ConnectionRefusedError,
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):
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log.warning(f"{ctx.chan} went down?")
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for ctx_set in topics2ctxs.values():
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ctx_set.discard(ctx)
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if not get_topics():
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log.warning(f"No subscribers left for {pub_gen}")
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break
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def modify_subs(topics2ctxs, topics, ctx):
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"""Absolute symbol subscription list for each quote stream.
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Effectively a symbol subscription api.
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"""
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log.info(f"{ctx.chan.uid} changed subscription to {topics}")
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# update map from each symbol to requesting client's chan
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for topic in topics:
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topics2ctxs.setdefault(topic, set()).add(ctx)
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# remove any existing symbol subscriptions if symbol is not
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# found in ``symbols``
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# TODO: this can likely be factored out into the pub-sub api
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for topic in filter(
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lambda topic: topic not in topics, topics2ctxs.copy()
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):
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ctx_set = topics2ctxs.get(topic)
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ctx_set.discard(ctx)
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if not ctx_set:
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# pop empty sets which will trigger bg quoter task termination
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topics2ctxs.pop(topic)
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def pub(
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wrapped: typing.Callable = None,
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*,
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tasks: Set[str] = set(),
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):
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"""Publisher async generator decorator.
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A publisher can be called multiple times from different actors but
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will only spawn a finite set of internal tasks to stream values to
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each caller. The ``tasks: Set[str]`` argument to the decorator
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specifies the names of the mutex set of publisher tasks. When the
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publisher function is called, an argument ``task_name`` must be
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passed to specify which task (of the set named in ``tasks``) should
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be used. This allows for using the same publisher with different
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input (arguments) without allowing more concurrent tasks then
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necessary.
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Values yielded from the decorated async generator must be
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``Dict[str, Dict[str, Any]]`` where the fist level key is the topic
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string and determines which subscription the packet will be
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delivered to and the value is a packet ``Dict[str, Any]`` by default
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of the form:
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.. ::python
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{topic: str: value: Any}
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The caller can instead opt to pass a ``packetizer`` callback who's
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return value will be delivered as the published response.
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The decorated async generator function must accept an argument
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:func:`get_topics` which dynamically returns the tuple of current
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subscriber topics:
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.. code:: python
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from tractor.msg import pub
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@pub(tasks={'source_1', 'source_2'})
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async def pub_service(get_topics):
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data = await web_request(endpoints=get_topics())
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for item in data:
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yield data['key'], data
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The publisher must be called passing in the following arguments:
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- ``topics: Set[str]`` the topic sequence or "subscriptions"
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- ``task_name: str`` the task to use (if ``tasks`` was passed)
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- ``ctx: Context`` the tractor context (only needed if calling the
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pub func without a nursery, otherwise this is provided implicitly)
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- packetizer: ``Callable[[str, Any], Any]`` a callback who receives
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the topic and value from the publisher function each ``yield`` such that
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whatever is returned is sent as the published value to subscribers of
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that topic. By default this is a dict ``{topic: value}``.
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As an example, to make a subscriber call the above function:
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.. code:: python
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from functools import partial
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import tractor
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async with tractor.open_nursery() as n:
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portal = n.run_in_actor(
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'publisher', # actor name
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partial( # func to execute in it
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pub_service,
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topics=('clicks', 'users'),
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task_name='source1',
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)
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)
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async for value in portal.result():
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print(f"Subscriber received {value}")
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Here, you don't need to provide the ``ctx`` argument since the
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remote actor provides it automatically to the spawned task. If you
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were to call ``pub_service()`` directly from a wrapping function you
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would need to provide this explicitly.
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Remember you only need this if you need *a finite set of tasks*
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running in a single actor to stream data to an arbitrary number of
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subscribers. If you are ok to have a new task running for every call
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to ``pub_service()`` then probably don't need this.
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"""
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# handle the decorator not called with () case
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if wrapped is None:
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return partial(pub, tasks=tasks)
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task2lock: Dict[Union[str, None], trio.StrictFIFOLock] = {
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None: trio.StrictFIFOLock()}
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for name in tasks:
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task2lock[name] = trio.StrictFIFOLock()
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@wrapt.decorator
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async def wrapper(agen, instance, args, kwargs):
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# this is used to extract arguments properly as per
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# the `wrapt` docs
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async def _execute(
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ctx: Context,
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topics: Set[str],
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*args,
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# *,
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task_name: str = None,
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packetizer: Callable = None,
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**kwargs,
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):
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if tasks and task_name is None:
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raise TypeError(
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f"{agen} must be called with a `task_name` named "
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f"argument with a falue from {tasks}")
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ss = current_actor().statespace
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lockmap = ss.setdefault('_pubtask2lock', task2lock)
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lock = lockmap[task_name]
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all_subs = ss.setdefault('_subs', {})
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topics2ctxs = all_subs.setdefault(task_name, {})
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try:
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modify_subs(topics2ctxs, topics, ctx)
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# block and let existing feed task deliver
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# stream data until it is cancelled in which case
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# the next waiting task will take over and spawn it again
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async with lock:
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# no data feeder task yet; so start one
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respawn = True
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while respawn:
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respawn = False
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log.info(
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f"Spawning data feed task for {funcname}")
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try:
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# unblocks when no more symbols subscriptions exist
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# and the streamer task terminates
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await fan_out_to_ctxs(
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pub_async_gen_func=partial(
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agen, *args, **kwargs),
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topics2ctxs=topics2ctxs,
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packetizer=packetizer,
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)
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log.info(
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f"Terminating stream task {task_name or ''}"
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f" for {agen.__name__}")
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except trio.BrokenResourceError:
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log.exception("Respawning failed data feed task")
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respawn = True
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finally:
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# remove all subs for this context
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modify_subs(topics2ctxs, (), ctx)
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# if there are truly no more subscriptions with this broker
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# drop from broker subs dict
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if not any(topics2ctxs.values()):
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log.info(
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f"No more subscriptions for publisher {task_name}")
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# invoke it
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await _execute(*args, **kwargs)
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funcname = wrapped.__name__
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if not inspect.isasyncgenfunction(wrapped):
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raise TypeError(
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f"Publisher {funcname} must be an async generator function"
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)
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if 'get_topics' not in inspect.signature(wrapped).parameters:
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raise TypeError(
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f"Publisher async gen {funcname} must define a "
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"`get_topics` argument"
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)
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# XXX: manually monkey the wrapped function since
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# ``wrapt.decorator`` doesn't seem to want to play nice with its
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# whole "adapter" thing...
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wrapped._tractor_stream_function = True # type: ignore
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return wrapper(wrapped)
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