Source code for distributed.variable

import asyncio
from collections import defaultdict
from contextlib import suppress
import logging
import uuid

from tlz import merge

from .client import Future, Client
from .utils import tokey, log_errors, TimeoutError, parse_timedelta
from .worker import get_client

logger = logging.getLogger(__name__)


class VariableExtension:
    """ An extension for the scheduler to manage queues

    This adds the following routes to the scheduler

    *  variable-set
    *  variable-get
    *  variable-delete
    """

    def __init__(self, scheduler):
        self.scheduler = scheduler
        self.variables = dict()
        self.waiting = defaultdict(set)
        self.waiting_conditions = defaultdict(asyncio.Condition)
        self.started = asyncio.Condition()

        self.scheduler.handlers.update(
            {"variable_set": self.set, "variable_get": self.get}
        )

        self.scheduler.stream_handlers["variable-future-release"] = self.future_release
        self.scheduler.stream_handlers["variable_delete"] = self.delete

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

    async def set(self, comm=None, name=None, key=None, data=None, client=None):
        if key is not None:
            record = {"type": "Future", "value": key}
            self.scheduler.client_desires_keys(keys=[key], client="variable-%s" % name)
        else:
            record = {"type": "msgpack", "value": data}
        try:
            old = self.variables[name]
        except KeyError:
            pass
        else:
            if old["type"] == "Future" and old["value"] != key:
                asyncio.ensure_future(self.release(old["value"], name))
        if name not in self.variables:
            async with self.started:
                self.started.notify_all()
        self.variables[name] = record

    async def release(self, key, name):
        while self.waiting[key, name]:
            async with self.waiting_conditions[name]:
                await self.waiting_conditions[name].wait()

        self.scheduler.client_releases_keys(keys=[key], client="variable-%s" % name)
        del self.waiting[key, name]

    async def future_release(self, name=None, key=None, token=None, client=None):
        self.waiting[key, name].remove(token)
        if not self.waiting[key, name]:
            async with self.waiting_conditions[name]:
                self.waiting_conditions[name].notify_all()

    async def get(self, comm=None, name=None, client=None, timeout=None):
        start = self.scheduler.loop.time()
        while name not in self.variables:
            if timeout is not None:
                left = timeout - (self.scheduler.loop.time() - start)
            else:
                left = None
            if left and left < 0:
                raise TimeoutError()
            try:

                async def _():  # Python 3.6 is odd and requires special help here
                    await self.started.acquire()
                    await self.started.wait()

                await asyncio.wait_for(_(), timeout=left)
            finally:
                with suppress(RuntimeError):  # Python 3.6 loses lock on finally clause
                    self.started.release()

        record = self.variables[name]
        if record["type"] == "Future":
            key = record["value"]
            token = uuid.uuid4().hex
            ts = self.scheduler.tasks.get(key)
            state = ts.state if ts is not None else "lost"
            msg = {"token": token, "state": state}
            if state == "erred":
                msg["exception"] = ts.exception_blame.exception
                msg["traceback"] = ts.exception_blame.traceback
            record = merge(record, msg)
            self.waiting[key, name].add(token)
        return record

    async def delete(self, comm=None, name=None, client=None):
        with log_errors():
            try:
                old = self.variables[name]
            except KeyError:
                pass
            else:
                if old["type"] == "Future":
                    await self.release(old["value"], name)
            with suppress(KeyError):
                del self.waiting_conditions[name]
            with suppress(KeyError):
                del self.variables[name]

            self.scheduler.remove_client("variable-%s" % name)


[docs]class Variable: """ Distributed Global Variable This allows multiple clients to share futures and data between each other with a single mutable variable. All metadata is sequentialized through the scheduler. Race conditions can occur. Values must be either Futures or msgpack-encodable data (ints, lists, strings, etc..) All data will be kept and sent through the scheduler, so it is wise not to send too much. If you want to share a large amount of data then ``scatter`` it and share the future instead. .. warning:: This object is experimental and has known issues in Python 2 Parameters ---------- name: string (optional) Name used by other clients and the scheduler to identify the variable. If not given, a random name will be generated. client: Client (optional) Client used for communication with the scheduler. Defaults to the value of ``Client.current()``. Examples -------- >>> from dask.distributed import Client, Variable # doctest: +SKIP >>> client = Client() # doctest: +SKIP >>> x = Variable('x') # doctest: +SKIP >>> x.set(123) # docttest: +SKIP >>> x.get() # docttest: +SKIP 123 >>> future = client.submit(f, x) # doctest: +SKIP >>> x.set(future) # doctest: +SKIP See Also -------- Queue: shared multi-producer/multi-consumer queue between clients """ def __init__(self, name=None, client=None, maxsize=0): self.client = client or Client.current() self.name = name or "variable-" + uuid.uuid4().hex async def _set(self, value): if isinstance(value, Future): await self.client.scheduler.variable_set( key=tokey(value.key), name=self.name ) else: await self.client.scheduler.variable_set(data=value, name=self.name)
[docs] def set(self, value, **kwargs): """ Set the value of this variable Parameters ---------- value: Future or object Must be either a Future or a msgpack-encodable value """ return self.client.sync(self._set, value, **kwargs)
async def _get(self, timeout=None): d = await self.client.scheduler.variable_get( timeout=timeout, name=self.name, client=self.client.id ) if d["type"] == "Future": value = Future(d["value"], self.client, inform=True, state=d["state"]) if d["state"] == "erred": value._state.set_error(d["exception"], d["traceback"]) self.client._send_to_scheduler( { "op": "variable-future-release", "name": self.name, "key": d["value"], "token": d["token"], } ) else: value = d["value"] return value
[docs] def get(self, timeout=None, **kwargs): """ Get the value of this variable 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) return self.client.sync(self._get, timeout=timeout, **kwargs)
[docs] def delete(self): """ Delete this variable Caution, this affects all clients currently pointing to this variable. """ if self.client.status == "running": # TODO: can leave zombie futures self.client._send_to_scheduler({"op": "variable_delete", "name": self.name})
def __getstate__(self): return (self.name, self.client.scheduler.address) def __setstate__(self, state): name, address = state try: client = get_client(address) assert client.scheduler.address == address except (AttributeError, AssertionError): client = Client(address, set_as_default=False) self.__init__(name=name, client=client)