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fix: data race between GET and INVALIDATE

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Fix for the documented example given here: https://redis.io/docs/latest/develop/reference/client-side-caching/#avoiding-race-conditions
This commit is contained in:
Ankush Menat 2025-01-07 11:06:46 +05:30
parent 73dc99275d
commit 8dd4ad53e2
1 changed files with 9 additions and 1 deletions
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10
frappe/utils/redis_wrapper.py
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@ -410,6 +410,7 @@ class _TrackedConnection(redis.Connection):
CachedValue = namedtuple("CachedValue", ["value", "expiry"])
_PLACEHOLDER_VALUE = CachedValue(value=None, expiry=-1)
class ClientCache:
@ -469,6 +470,10 @@ class ClientCache:
except KeyError:
pass # cache miss
# Store a placeholder value to detect race between GET and parallel invalidation.
with self.lock:
self.cache[key] = _PLACEHOLDER_VALUE
val = self.redis.get_value(key, shared=True, use_local_cache=not self.cache_healthy)
# Note: We should not "cache" the cache-misses in client cache.
@ -479,7 +484,10 @@ class ClientCache:
self.ensure_max_size()
with self.lock:
self.cache[key] = CachedValue(value=val, expiry=time.monotonic() + self.local_ttl)
# Note: If our placeholder value is not present then it's possible that value we just
# got is invalidated, so we should not store it in local cache.
if key in self.cache:
self.cache[key] = CachedValue(value=val, expiry=time.monotonic() + self.local_ttl)
return val