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from __future__ import annotations
import asyncio
from distributed.metrics import time
class ResourceLimiter:
"""Limit an abstract resource
This allows us to track usage of an abstract resource. If the usage of this
resources goes beyond a defined maxvalue, we can block further execution
Example::
limiter = ResourceLimiter(2)
limiter.increase(1)
limiter.increase(2)
limiter.decrease(1)
# This will block since we're still not below maxvalue
await limiter.wait_for_available()
"""
def __init__(self, maxvalue: int) -> None:
self._maxvalue = maxvalue
self._acquired = 0
self._condition = asyncio.Condition()
self._waiters = 0
self.time_blocked_total = 0.0
self.time_blocked_avg = 0.0
def __repr__(self) -> str:
return f"<ResourceLimiter maxvalue: {self._maxvalue} available: {self.available()}>"
def available(self) -> int:
"""How far can the value be increased before blocking"""
return max(0, self._maxvalue - self._acquired)
def free(self) -> bool:
"""Return True if nothing has been acquired / the limiter is in a neutral state"""
return self._acquired == 0
async def wait_for_available(self) -> None:
"""Block until the counter drops below maxvalue"""
start = time()
duration = 0
try:
if self.available():
return
async with self._condition:
self._waiters += 1
await self._condition.wait_for(self.available)
self._waiters -= 1
duration = time() - start
finally:
self.time_blocked_total += duration
self.time_blocked_avg = self.time_blocked_avg * 0.9 + duration * 0.1
def increase(self, value: int) -> None:
"""Increase the internal counter by value"""
self._acquired += value
async def decrease(self, value: int) -> None:
"""Decrease the internal counter by value"""
if value > self._acquired:
raise RuntimeError(
f"Cannot release more than what was acquired! release: {value} acquired: {self._acquired}"
)
self._acquired -= value
async with self._condition:
self._condition.notify_all()
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