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173 | import asyncio
from collections import defaultdict, deque
import logging
import uuid
from .client import Client
from .utils import log_errors, TimeoutError
from .worker import get_worker
from .utils import parse_timedelta
logger = logging.getLogger(__name__)
class LockExtension:
"""An extension for the scheduler to manage Locks
This adds the following routes to the scheduler
* lock_acquire
* lock_release
"""
def __init__(self, scheduler):
self.scheduler = scheduler
self.events = defaultdict(deque)
self.ids = dict()
self.scheduler.handlers.update(
{"lock_acquire": self.acquire, "lock_release": self.release}
)
self.scheduler.extensions["locks"] = self
async def acquire(self, comm=None, name=None, id=None, timeout=None):
with log_errors():
if isinstance(name, list):
name = tuple(name)
if name not in self.ids:
result = True
else:
while name in self.ids:
event = asyncio.Event()
self.events[name].append(event)
future = event.wait()
if timeout is not None:
future = asyncio.wait_for(future, timeout)
try:
await future
except TimeoutError:
result = False
break
else:
result = True
finally:
event2 = self.events[name].popleft()
assert event is event2
if result:
assert name not in self.ids
self.ids[name] = id
return result
def release(self, comm=None, name=None, id=None):
with log_errors():
if isinstance(name, list):
name = tuple(name)
if self.ids.get(name) != id:
raise ValueError("This lock has not yet been acquired")
del self.ids[name]
if self.events[name]:
self.scheduler.loop.add_callback(self.events[name][0].set)
else:
del self.events[name]
class Lock:
"""Distributed Centralized Lock
Parameters
----------
name: string (optional)
Name of the lock to acquire. Choosing the same name allows two
disconnected processes to coordinate a lock. If not given, a random
name will be generated.
client: Client (optional)
Client to use for communication with the scheduler. If not given, the
default global client will be used.
Examples
--------
>>> lock = Lock('x') # doctest: +SKIP
>>> lock.acquire(timeout=1) # doctest: +SKIP
>>> # do things with protected resource
>>> lock.release() # doctest: +SKIP
"""
def __init__(self, name=None, client=None):
try:
self.client = client or Client.current()
except ValueError:
# Initialise new client
self.client = get_worker().client
self.name = name or "lock-" + uuid.uuid4().hex
self.id = uuid.uuid4().hex
self._locked = False
def acquire(self, blocking=True, timeout=None):
"""Acquire the lock
Parameters
----------
blocking : bool, optional
If false, don't wait on the lock in the scheduler at all.
timeout : string or number or timedelta, optional
Seconds to wait on the lock in the scheduler. This does not
include local coroutine time, network transfer time, etc..
It is forbidden to specify a timeout when blocking is false.
Instead of number of seconds, it is also possible to specify
a timedelta in string format, e.g. "200ms".
Examples
--------
>>> lock = Lock('x') # doctest: +SKIP
>>> lock.acquire(timeout="1s") # doctest: +SKIP
Returns
-------
True or False whether or not it sucessfully acquired the lock
"""
timeout = parse_timedelta(timeout)
if not blocking:
if timeout is not None:
raise ValueError("can't specify a timeout for a non-blocking call")
timeout = 0
result = self.client.sync(
self.client.scheduler.lock_acquire,
name=self.name,
id=self.id,
timeout=timeout,
)
self._locked = True
return result
def release(self):
""" Release the lock if already acquired """
if not self.locked():
raise ValueError("Lock is not yet acquired")
result = self.client.sync(
self.client.scheduler.lock_release, name=self.name, id=self.id
)
self._locked = False
return result
def locked(self):
return self._locked
def __enter__(self):
self.acquire()
return self
def __exit__(self, *args, **kwargs):
self.release()
async def __aenter__(self):
await self.acquire()
return self
async def __aexit__(self, *args, **kwargs):
await self.release()
def __reduce__(self):
return (Lock, (self.name,))
|