Source code for distributed.pubsub

import asyncio
from collections import defaultdict, deque
from contextlib import suppress
import logging
import threading
import weakref

from .core import CommClosedError
from .metrics import time
from .utils import sync, TimeoutError, parse_timedelta
from .protocol.serialize import to_serialize

logger = logging.getLogger(__name__)


class PubSubSchedulerExtension:
    """ Extend Dask's scheduler with routes to handle PubSub machinery """

    def __init__(self, scheduler):
        self.scheduler = scheduler
        self.publishers = defaultdict(set)
        self.subscribers = defaultdict(set)
        self.client_subscribers = defaultdict(set)

        self.scheduler.handlers.update({"pubsub_add_publisher": self.add_publisher})

        self.scheduler.stream_handlers.update(
            {
                "pubsub-add-subscriber": self.add_subscriber,
                "pubsub-remove-publisher": self.remove_publisher,
                "pubsub-remove-subscriber": self.remove_subscriber,
                "pubsub-msg": self.handle_message,
            }
        )

        self.scheduler.extensions["pubsub"] = self

    def add_publisher(self, comm=None, name=None, worker=None):
        logger.debug("Add publisher: %s %s", name, worker)
        self.publishers[name].add(worker)
        return {
            "subscribers": {addr: {} for addr in self.subscribers[name]},
            "publish-scheduler": name in self.client_subscribers
            and len(self.client_subscribers[name]) > 0,
        }

    def add_subscriber(self, comm=None, name=None, worker=None, client=None):
        if worker:
            logger.debug("Add worker subscriber: %s %s", name, worker)
            self.subscribers[name].add(worker)
            for pub in self.publishers[name]:
                self.scheduler.worker_send(
                    pub,
                    {"op": "pubsub-add-subscriber", "address": worker, "name": name},
                )
        elif client:
            logger.debug("Add client subscriber: %s %s", name, client)
            for pub in self.publishers[name]:
                self.scheduler.worker_send(
                    pub,
                    {"op": "pubsub-publish-scheduler", "name": name, "publish": True},
                )
            self.client_subscribers[name].add(client)

    def remove_publisher(self, comm=None, name=None, worker=None):
        if worker in self.publishers[name]:
            logger.debug("Remove publisher: %s %s", name, worker)
            self.publishers[name].remove(worker)

            if not self.subscribers[name] and not self.publishers[name]:
                del self.subscribers[name]
                del self.publishers[name]

    def remove_subscriber(self, comm=None, name=None, worker=None, client=None):
        if worker:
            logger.debug("Remove worker subscriber: %s %s", name, worker)
            self.subscribers[name].remove(worker)
            for pub in self.publishers[name]:
                self.scheduler.worker_send(
                    pub,
                    {"op": "pubsub-remove-subscriber", "address": worker, "name": name},
                )
        elif client:
            logger.debug("Remove client subscriber: %s %s", name, client)
            self.client_subscribers[name].remove(client)
            if not self.client_subscribers[name]:
                del self.client_subscribers[name]
                for pub in self.publishers[name]:
                    self.scheduler.worker_send(
                        pub,
                        {
                            "op": "pubsub-publish-scheduler",
                            "name": name,
                            "publish": False,
                        },
                    )

        if not self.subscribers[name] and not self.publishers[name]:
            logger.debug("Remove PubSub topic %s", name)
            del self.subscribers[name]
            del self.publishers[name]

    def handle_message(self, name=None, msg=None, worker=None, client=None):
        for c in list(self.client_subscribers[name]):
            try:
                self.scheduler.client_comms[c].send(
                    {"op": "pubsub-msg", "name": name, "msg": msg}
                )
            except (KeyError, CommClosedError):
                self.remove_subscriber(name=name, client=c)

        if client:
            for sub in self.subscribers[name]:
                self.scheduler.worker_send(
                    sub, {"op": "pubsub-msg", "name": name, "msg": msg}
                )


class PubSubWorkerExtension:
    """ Extend Dask's Worker with routes to handle PubSub machinery """

    def __init__(self, worker):
        self.worker = worker
        self.worker.stream_handlers.update(
            {
                "pubsub-add-subscriber": self.add_subscriber,
                "pubsub-remove-subscriber": self.remove_subscriber,
                "pubsub-msg": self.handle_message,
                "pubsub-publish-scheduler": self.publish_scheduler,
            }
        )

        self.subscribers = defaultdict(weakref.WeakSet)
        self.publishers = defaultdict(weakref.WeakSet)
        self.publish_to_scheduler = defaultdict(lambda: False)

        self.worker.extensions["pubsub"] = self  # circular reference

    def add_subscriber(self, name=None, address=None, **info):
        for pub in self.publishers[name]:
            pub.subscribers[address] = info

    def remove_subscriber(self, name=None, address=None):
        for pub in self.publishers[name]:
            del pub.subscribers[address]

    def publish_scheduler(self, name=None, publish=None):
        self.publish_to_scheduler[name] = publish

    async def handle_message(self, name=None, msg=None):
        for sub in self.subscribers.get(name, []):
            await sub._put(msg)

    def trigger_cleanup(self):
        self.worker.loop.add_callback(self.cleanup)

    def cleanup(self):
        for name, s in dict(self.subscribers).items():
            if not len(s):
                msg = {"op": "pubsub-remove-subscriber", "name": name}
                self.worker.batched_stream.send(msg)
                del self.subscribers[name]

        for name, p in dict(self.publishers).items():
            if not len(p):
                msg = {"op": "pubsub-remove-publisher", "name": name}
                self.worker.batched_stream.send(msg)
                del self.publishers[name]
                del self.publish_to_scheduler[name]


class PubSubClientExtension:
    """ Extend Dask's Client with handlers to handle PubSub machinery """

    def __init__(self, client):
        self.client = client
        self.client._stream_handlers.update({"pubsub-msg": self.handle_message})

        self.subscribers = defaultdict(weakref.WeakSet)
        self.client.extensions["pubsub"] = self  # TODO: circular reference

    async def handle_message(self, name=None, msg=None):
        for sub in self.subscribers[name]:
            await sub._put(msg)

        if not self.subscribers[name]:
            self.client.scheduler_comm.send(
                {"op": "pubsub-remove-subscribers", "name": name}
            )

    def trigger_cleanup(self):
        self.client.loop.add_callback(self.cleanup)

    def cleanup(self):
        for name, s in self.subscribers.items():
            if not s:
                msg = {"op": "pubsub-remove-subscriber", "name": name}
                self.client.scheduler_comm.send(msg)


[docs]class Pub: """Publish data with Publish-Subscribe pattern This allows clients and workers to directly communicate data between each other with a typical Publish-Subscribe pattern. This involves two components, Pub objects, into which we put data: >>> pub = Pub('my-topic') >>> pub.put(123) And Sub objects, from which we collect data: >>> sub = Sub('my-topic') >>> sub.get() 123 Many Pub and Sub objects can exist for the same topic. All data sent from any Pub will be sent to all Sub objects on that topic that are currently connected. Pub's and Sub's find each other using the scheduler, but they communicate directly with each other without coordination from the scheduler. Pubs and Subs use the central scheduler to find each other, but not to mediate the communication. This means that there is very little additional latency or overhead, and they are appropriate for very frequent data transfers. For context, most data transfer first checks with the scheduler to find which workers should participate, and then does direct worker-to-worker transfers. This checking in with the scheduler provides some stability guarantees, but also adds in a few extra network hops. PubSub doesn't do this, and so is faster, but also can easily drop messages if Pubs or Subs disappear without notice. When using a Pub or Sub from a Client all communications will be routed through the scheduler. This can cause some performance degradation. Pubs and Subs only operate at top-speed when they are both on workers. Parameters ---------- name: object (msgpack serializable) The name of the group of Pubs and Subs on which to participate. worker: Worker (optional) The worker to be used for publishing data. Defaults to the value of ```get_worker()```. If given, ``client`` must be ``None``. client: Client (optional) Client used for communication with the scheduler. Defaults to the value of ``get_client()``. If given, ``worker`` must be ``None``. Examples -------- >>> pub = Pub('my-topic') >>> sub = Sub('my-topic') >>> pub.put([1, 2, 3]) >>> sub.get() [1, 2, 3] You can also use sub within a for loop: >>> for msg in sub: # doctest: +SKIP ... print(msg) or an async for loop >>> async for msg in sub: # doctest: +SKIP ... print(msg) Similarly the ``.get`` method will return an awaitable if used by an async client or within the IOLoop thread of a worker >>> await sub.get() # doctest: +SKIP You can see the set of connected worker subscribers by looking at the ``.subscribers`` attribute: >>> pub.subscribers {'tcp://...': {}, 'tcp://...': {}} See Also -------- Sub """ def __init__(self, name, worker=None, client=None): if worker is None and client is None: from distributed import get_worker, get_client try: worker = get_worker() except Exception: client = get_client() self.subscribers = dict() self.worker = worker self.client = client assert client or worker if self.worker: self.scheduler = self.worker.scheduler self.loop = self.worker.loop elif self.client: self.scheduler = self.client.scheduler self.loop = self.client.loop self.name = name self._started = False self._buffer = [] self.loop.add_callback(self._start) if self.worker: pubsub = self.worker.extensions["pubsub"] self.loop.add_callback(pubsub.publishers[name].add, self) weakref.finalize(self, pubsub.trigger_cleanup) async def _start(self): if self.worker: result = await self.scheduler.pubsub_add_publisher( name=self.name, worker=self.worker.address ) pubsub = self.worker.extensions["pubsub"] self.subscribers.update(result["subscribers"]) pubsub.publish_to_scheduler[self.name] = result["publish-scheduler"] self._started = True for msg in self._buffer: self.put(msg) del self._buffer[:] def _put(self, msg): if not self._started: self._buffer.append(msg) return data = {"op": "pubsub-msg", "name": self.name, "msg": to_serialize(msg)} if self.worker: for sub in self.subscribers: self.worker.send_to_worker(sub, data) if self.worker.extensions["pubsub"].publish_to_scheduler[self.name]: self.worker.batched_stream.send(data) elif self.client: self.client.scheduler_comm.send(data)
[docs] def put(self, msg): """ Publish a message to all subscribers of this topic """ self.loop.add_callback(self._put, msg)
def __repr__(self): return "<Pub: {}>".format(self.name) __str__ = __repr__
[docs]class Sub: """Subscribe to a Publish/Subscribe topic See Also -------- Pub: for full docstring """ def __init__(self, name, worker=None, client=None): if worker is None and client is None: from distributed.worker import get_worker, get_client try: worker = get_worker() except Exception: client = get_client() self.worker = worker self.client = client if self.worker: self.loop = self.worker.loop elif self.client: self.loop = self.client.loop self.name = name self.buffer = deque() if self.worker: pubsub = self.worker.extensions["pubsub"] elif self.client: pubsub = self.client.extensions["pubsub"] self.loop.add_callback(pubsub.subscribers[name].add, self) msg = {"op": "pubsub-add-subscriber", "name": self.name} if self.worker: self.loop.add_callback(self.worker.batched_stream.send, msg) elif self.client: self.loop.add_callback(self.client.scheduler_comm.send, msg) else: raise Exception() weakref.finalize(self, pubsub.trigger_cleanup) @property def condition(self): try: return self._condition except AttributeError: self._condition = asyncio.Condition() return self._condition async def _get(self, timeout=None): start = time() while not self.buffer: if timeout is not None: timeout2 = timeout - (time() - start) if timeout2 < 0: raise TimeoutError() else: timeout2 = None async def _(): await self.condition.acquire() await self.condition.wait() try: await asyncio.wait_for(_(), timeout2) finally: with suppress(RuntimeError): # Python 3.6 fails here sometimes self.condition.release() return self.buffer.popleft() __anext__ = _get
[docs] def get(self, timeout=None): """Get a single message Parameters ---------- timeout: number or string or timedelta, optional Time in seconds to wait before timing out. Instead of number of seconds, it is also possible to specify a timedelta in string format, e.g. "200ms". """ timeout = parse_timedelta(timeout) if self.client: return self.client.sync(self._get, timeout=timeout) elif self.worker.thread_id == threading.get_ident(): return self._get() else: if self.buffer: # fastpath return self.buffer.popleft() return sync(self.loop, self._get, timeout=timeout)
next = __next__ = get def __iter__(self): return self def __aiter__(self): return self async def _put(self, msg): self.buffer.append(msg) async with self.condition: self.condition.notify() def __repr__(self): return "<Sub: {}>".format(self.name) __str__ = __repr__