Source code for distributed.lock

from __future__ import annotations

import asyncio
import logging
import uuid
from collections import defaultdict, deque

from dask.utils import parse_timedelta

from distributed.client import Client
from distributed.utils import TimeoutError, log_errors
from distributed.worker import get_worker

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}
        )

    @log_errors
    async def acquire(self, name=None, id=None, timeout=None):
        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

    @log_errors
    def release(self, name=None, id=None):
        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]


[docs]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
[docs] 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
[docs] 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, exc_type, exc_value, traceback): self.release() async def __aenter__(self): await self.acquire() return self async def __aexit__(self, exc_type, exc_value, traceback): await self.release() def __reduce__(self): return (Lock, (self.name,))