text: 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, stream=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, stream=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, stream=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]
  
  
  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)
  
      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
  
      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)
  
      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)
  