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// Copyright 2018 The Hugo Authors. All rights reserved.
//
// 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 namedmemcache provides a memory cache with a named lock. This is suitable
// for situations where creating the cached resource can be time consuming or otherwise
// resource hungry, or in situations where a "once only per key" is a requirement.
package namedmemcache
import (
"sync"
"github.com/BurntSushi/locker"
)
// Cache holds the cached values.
type Cache struct {
nlocker *locker.Locker
cache map[string]cacheEntry
mu sync.RWMutex
}
type cacheEntry struct {
value interface{}
err error
}
// New creates a new cache.
func New() *Cache {
return &Cache{
nlocker: locker.NewLocker(),
cache: make(map[string]cacheEntry),
}
}
// Clear clears the cache state.
func (c *Cache) Clear() {
c.mu.Lock()
defer c.mu.Unlock()
c.cache = make(map[string]cacheEntry)
c.nlocker = locker.NewLocker()
}
// GetOrCreate tries to get the value with the given cache key, if not found
// create will be called and cached.
// This method is thread safe. It also guarantees that the create func for a given
// key is invoked only once for this cache.
func (c *Cache) GetOrCreate(key string, create func() (interface{}, error)) (interface{}, error) {
c.mu.RLock()
entry, found := c.cache[key]
c.mu.RUnlock()
if found {
return entry.value, entry.err
}
c.nlocker.Lock(key)
defer c.nlocker.Unlock(key)
// Create it.
value, err := create()
c.mu.Lock()
c.cache[key] = cacheEntry{value: value, err: err}
c.mu.Unlock()
return value, err
}
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