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Use a sentinel instead of None for cache presence

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This commit is contained in:
Zoe Roux 2024-01-08 01:03:01 +01:00
parent b180429505
commit 0b55bd7dbb
1 changed files with 16 additions and 10 deletions
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26
scanner/scanner/cache.py
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@ -1,9 +1,15 @@
import asyncio
from datetime import datetime, timedelta
from functools import wraps
from typing import Any, Optional, Tuple
from typing import Any, Optional, Tuple, Final, Literal
from enum import Enum
type Cache = dict[Any, Tuple[Optional[asyncio.Event], Optional[datetime], Any]]
# Waiting for https://github.com/python/typing/issues/689 for better sentinels
class Sentinel(Enum):
NoneSentinel = 0
none: Final = Sentinel.NoneSentinel
type Cache = dict[Any, Tuple[asyncio.Event | Literal[none], datetime | Literal[none], Any]]
def cache(ttl: timedelta, cache: Optional[Cache] = None, typed=False):
"""
@ -25,19 +31,19 @@ def cache(ttl: timedelta, cache: Optional[Cache] = None, typed=False):
async def wrapper(*args, **kwargs):
key = make_key(args, kwargs, typed)
ret = cache.get(key, (None, None, None))
ret = cache.get(key, (none, none, none))
# First check if the same method is already running and wait for it.
if ret[0] is not None:
if ret[0] != none:
await ret[0].wait()
ret = cache.get(key, (None, None, None))
if ret[2] is None:
ret = cache.get(key, (none, none, none))
if ret[2] == none:
# ret[2] can be None if the cached method failed. if that is the case, run again.
return await wrapper(*args, **kwargs)
return ret[2]
# Return the cached result if it exits and is not expired
if (
ret[2] is not None
and ret[1] is not None
ret[2] != none
and ret[1] != none
and datetime.now() - ret[1] < ttl
):
return ret[2]
@ -50,7 +56,7 @@ def cache(ttl: timedelta, cache: Optional[Cache] = None, typed=False):
async def exec_as_cache(cache: Cache, key, f):
event = asyncio.Event()
cache[key] = (event, None, None)
cache[key] = (event, none, none)
try:
result = await f()
except:
@ -58,7 +64,7 @@ async def exec_as_cache(cache: Cache, key, f):
event.set()
raise
cache[key] = (None, datetime.now(), result)
cache[key] = (none, datetime.now(), result)
event.set()
return result