Source code for betty.concurrent

"""
Provide utilities for concurrent programming.
"""

import asyncio
import threading
import time
from abc import ABC, abstractmethod
from asyncio import sleep
from math import floor
from types import TracebackType
from typing import Self, final

from typing_extensions import override


[docs] class Lock(ABC): """ Provide an asynchronous lock. """ async def __aenter__(self): await self.acquire() async def __aexit__( self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None, ) -> None: await self.release()
[docs] @abstractmethod async def acquire(self, *, wait: bool = True) -> bool: """ Acquire the lock. """ pass
[docs] @abstractmethod async def release(self) -> None: """ Release the lock. """ pass
[docs] async def asynchronize_acquire(lock: threading.Lock, *, wait: bool = True) -> bool: """ Acquire a synchronous lock asynchronously. """ while not lock.acquire(blocking=False): if not wait: return False # Sleeping for zero seconds does not actually sleep, but gives the event # loop a chance to progress other tasks while we wait for another chance # to acquire the lock. await sleep(0) return True
[docs] @final class AsynchronizedLock(Lock): """ Make a sychronous (blocking) lock asynchronous (non-blocking). """ __slots__ = "_lock"
[docs] def __init__(self, lock: threading.Lock): self._lock = lock
[docs] @override async def acquire(self, *, wait: bool = True) -> bool: return await asynchronize_acquire(self._lock, wait=wait)
[docs] @override async def release(self) -> None: self._lock.release()
[docs] @classmethod def threading(cls) -> Self: """ Create a new thread-safe, asynchronous lock. """ return cls(threading.Lock())
[docs] @final class RateLimiter: """ Rate-limit operations. This class implements the `Token Bucket algorithm <https://en.wikipedia.org/wiki/Token_bucket>`_. This class is thread-safe. """ _PERIOD = 1
[docs] def __init__(self, maximum: int): self._lock = AsynchronizedLock.threading() self._maximum = maximum self._available: int | float = maximum # A Token Bucket fills as time passes. However, we want callers to be able to start # using the limiter immediately, so we 'preload' the first's period's tokens, and # set the last added time to the end of the first period. This ensures there is no # needless waiting if the number of tokens consumed in total is less than the limit # per period. self._last_add = time.monotonic() + self._PERIOD
def _add_tokens(self): now = time.monotonic() elapsed = now - self._last_add added = elapsed * self._maximum possibly_available = floor(self._available + added) if possibly_available > 0: self._available = min(possibly_available, self._maximum) self._last_add = now async def __aenter__(self) -> None: await self.wait() async def __aexit__( self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None, ) -> None: return
[docs] async def wait(self) -> None: """ Wait until an operation may be performed (again). """ async with self._lock: while self._available < 1: self._add_tokens() if self._available < 1: await asyncio.sleep(0.1) self._available -= 1