import asyncio
import logging
import uuid
from collections import defaultdict
from contextlib import suppress
from tlz import merge
from dask.utils import parse_timedelta, stringify
from .client import Client, Future
from .utils import TimeoutError, log_errors
from .worker import get_client, get_worker
logger = logging.getLogger(__name__)
class VariableExtension:
"""An extension for the scheduler to manage Variables
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:
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.
If not given, the default global client will be used.
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):
try:
self.client = client or Client.current()
except ValueError:
# Initialise new client
self.client = get_worker().client
self.name = name or "variable-" + uuid.uuid4().hex
async def _set(self, value):
if isinstance(value, Future):
await self.client.scheduler.variable_set(
key=stringify(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)