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cache.go
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cache.go
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// Copyright (c) 2016 Couchbase, Inc.
//
// 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 registry
import (
"fmt"
"sync"
)
var ErrAlreadyDefined = fmt.Errorf("item already defined")
type CacheBuild func(name string, config map[string]interface{}, cache *Cache) (interface{}, error)
type ConcurrentCache struct {
mutex sync.RWMutex
data map[string]interface{}
}
func NewConcurrentCache() *ConcurrentCache {
return &ConcurrentCache{
data: make(map[string]interface{}),
}
}
func (c *ConcurrentCache) ItemNamed(name string, cache *Cache, build CacheBuild) (interface{}, error) {
c.mutex.RLock()
item, cached := c.data[name]
if cached {
c.mutex.RUnlock()
return item, nil
}
// give up read lock
c.mutex.RUnlock()
// try to build it
newItem, err := build(name, nil, cache)
if err != nil {
return nil, err
}
// acquire write lock
c.mutex.Lock()
defer c.mutex.Unlock()
// check again because it could have been created while trading locks
item, cached = c.data[name]
if cached {
return item, nil
}
c.data[name] = newItem
return newItem, nil
}
func (c *ConcurrentCache) DefineItem(name string, typ string, config map[string]interface{}, cache *Cache, build CacheBuild) (interface{}, error) {
c.mutex.RLock()
_, cached := c.data[name]
if cached {
c.mutex.RUnlock()
return nil, ErrAlreadyDefined
}
// give up read lock so others lookups can proceed
c.mutex.RUnlock()
// really not there, try to build it
newItem, err := build(typ, config, cache)
if err != nil {
return nil, err
}
// now we've built it, acquire lock
c.mutex.Lock()
defer c.mutex.Unlock()
// check again because it could have been created while trading locks
_, cached = c.data[name]
if cached {
return nil, ErrAlreadyDefined
}
c.data[name] = newItem
return newItem, nil
}