import asyncio
from collections import defaultdict
from contextlib import suppress
import logging
import uuid
from tlz import merge
from dask.utils import stringify
from .client import Future, Client
from .utils import log_errors, TimeoutError, parse_timedelta
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:
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.
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)