"""
Provide utilities for concurrent programming.
"""
import asyncio
import threading
import time
from asyncio import sleep
from math import floor
from threading import Lock
from types import TracebackType
from typing import Self
from typing_extensions import override
from betty.asyncio import gather
class _Lock:
"""
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:
self.release()
async def acquire(self, *, wait: bool = True) -> bool:
"""
Acquire the lock.
"""
raise NotImplementedError
def release(self) -> None:
"""
Release the lock.
"""
raise NotImplementedError
[docs]
async def asynchronize_acquire(lock: 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]
class AsynchronizedLock(_Lock):
"""
Make a sychronous (blocking) lock asynchronous (non-blocking).
"""
__slots__ = "_lock"
[docs]
@override
async def acquire(self, *, wait: bool = True) -> bool:
acquisitions = await gather(*(lock.acquire(wait=wait) for lock in self._locks))
# We require all locks to be acquired, or none at all
# If one or more fail, release the others.
if False in acquisitions:
for lock, acquisition in zip(self._locks, acquisitions):
if acquisition:
lock.release()
return False
self._locked = True
return True
[docs]
@override
def release(self) -> None:
self._locked = False
for lock in self._locks:
lock.release()
[docs]
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
[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