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fix(site_cache): site cache thread safety (#28870)

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Identified two cases where site cache can break:

1. Other thread clears cache using clear_cache because of TTL or manual
   eviction.
2. Other thread pops the eliment we are about to read because of
   `maxsize` limit.

This change should fix both and even make it lil bit faster.
This commit is contained in:
Ankush Menat 2024-12-23 13:44:19 +05:30 • committed by GitHub
parent 197a49cf27
commit 17686eba3b
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GPG key ID: B5690EEEBB952194
1 changed files with 26 additions and 12 deletions
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38
frappe/utils/caching.py
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@ -117,23 +117,37 @@ def site_cache(ttl: int | None = None, maxsize: int | None = None) -> Callable:
@wraps(func)
def site_cache_wrapper(*args, **kwargs):
if site := getattr(frappe.local, "site", None):
func_call_key = __generate_request_cache_key(args, kwargs)
site = getattr(frappe.local, "site", None)
if not site:
return func(*args, **kwargs)
if hasattr(func, "ttl") and time.monotonic() >= func.expiration:
func.clear_cache()
func.expiration = time.monotonic() + func.ttl
func_call_key = __generate_request_cache_key(args, kwargs)
if hasattr(func, "maxsize") and len(_SITE_CACHE[func_key][site]) >= func.maxsize:
# Note: This implements FIFO eviction policy
_SITE_CACHE[func_key][site].pop(next(iter(_SITE_CACHE[func_key][site])), None)
if hasattr(func, "ttl") and time.monotonic() >= func.expiration:
func.clear_cache()
func.expiration = time.monotonic() + func.ttl
if func_call_key not in _SITE_CACHE[func_key][site]:
_SITE_CACHE[func_key][site][func_call_key] = func(*args, **kwargs)
# NOTE: Important things to consider from thread safety POV:
# 1. Other thread can issue clear_cache and delete entire func_key dictionary.
# 2. Other thread can pop the exact elemement we are reading if maxsize is hit.
return _SITE_CACHE[func_key][site][func_call_key]
# NOTE: Keep a local reference to dictionary of interest so it doesn't get swapped
site_specific_cache = _SITE_CACHE[func_key][site]
return func(*args, **kwargs)
try:
return site_specific_cache[func_call_key]
except KeyError:
# NOTE: This is just a cache miss
pass
if hasattr(func, "maxsize") and len(site_specific_cache) >= func.maxsize:
# Note: This implements FIFO eviction policy
site_specific_cache.pop(next(iter(site_specific_cache)), None)
result = func(*args, **kwargs)
site_specific_cache[func_call_key] = result
return result
return site_cache_wrapper