| // Copyright 2016 The LUCI Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package authdb |
| |
| import ( |
| "context" |
| "time" |
| |
| "go.chromium.org/luci/common/data/caching/lazyslot" |
| "go.chromium.org/luci/common/data/rand/mathrand" |
| ) |
| |
| // DBCacheUpdater knows how to update local in-memory copy of DB. |
| // |
| // Used by NewDBCache. |
| type DBCacheUpdater func(c context.Context, prev DB) (DB, error) |
| |
| // NewDBCache returns a provider of DB instances that uses local memory to |
| // cache DB instances for 5-10 seconds. It uses supplied callback to refetch DB |
| // from some permanent storage when cache expires. |
| // |
| // Even though the return value is technically a function, treat it as a heavy |
| // stateful object, since it has the cache of DB in its closure. |
| func NewDBCache(updater DBCacheUpdater) func(c context.Context) (DB, error) { |
| cacheSlot := lazyslot.Slot{} |
| return func(c context.Context) (DB, error) { |
| val, err := cacheSlot.Get(c, func(prev interface{}) (db interface{}, exp time.Duration, err error) { |
| prevDB, _ := prev.(DB) |
| if db, err = updater(c, prevDB); err == nil { |
| exp = 5*time.Second + time.Duration(mathrand.Get(c).Intn(5000))*time.Millisecond |
| } |
| return |
| }) |
| if err != nil { |
| return nil, err |
| } |
| return val.(DB), nil |
| } |
| } |