from __future__ import annotations
import asyncio
import logging
import threading
import weakref
from collections import defaultdict, deque
from dask.utils import parse_timedelta
from distributed.core import CommClosedError
from distributed.metrics import time
from distributed.protocol.serialize import to_serialize
from distributed.utils import TimeoutError, sync, wait_for
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,
}
)
def add_publisher(self, 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, 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, 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, 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(bool)
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)
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_client, get_worker
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 f"<Pub: {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_client, get_worker
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 wait_for(_(), timeout2)
finally:
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 f"<Sub: {self.name}>"
__str__ = __repr__