e00577f265
previously we just used a Go builtin map this was not safe for concurrent read/write and upon upgrading to Go 1.6 we were notified of the problem fixes #349
83 lines
2.2 KiB
Go
83 lines
2.2 KiB
Go
// Copyright (c) 2016 Couchbase, Inc.
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
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// except in compliance with the License. You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing, software distributed under the
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// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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// either express or implied. See the License for the specific language governing permissions
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// and limitations under the License.
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package registry
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import (
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"fmt"
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"sync"
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)
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var ErrAlreadyDefined = fmt.Errorf("item already defined")
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type CacheBuild func(name string, config map[string]interface{}, cache *Cache) (interface{}, error)
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type ConcurrentCache struct {
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mutex sync.RWMutex
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data map[string]interface{}
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}
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func NewConcurrentCache() *ConcurrentCache {
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return &ConcurrentCache{
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data: make(map[string]interface{}),
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}
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}
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func (c *ConcurrentCache) ItemNamed(name string, cache *Cache, build CacheBuild) (interface{}, error) {
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c.mutex.RLock()
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item, cached := c.data[name]
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if cached {
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c.mutex.RUnlock()
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return item, nil
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}
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// give up read lock
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c.mutex.RUnlock()
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// try to build it
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newItem, err := build(name, nil, cache)
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if err != nil {
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return nil, err
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}
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// acquire write lock
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c.mutex.Lock()
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defer c.mutex.Unlock()
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// check again because it could have been created while trading locks
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item, cached = c.data[name]
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if cached {
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return item, nil
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}
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c.data[name] = newItem
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return newItem, nil
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}
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func (c *ConcurrentCache) DefineItem(name string, typ string, config map[string]interface{}, cache *Cache, build CacheBuild) (interface{}, error) {
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c.mutex.RLock()
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_, cached := c.data[name]
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if cached {
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c.mutex.RUnlock()
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return nil, ErrAlreadyDefined
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}
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// give up read lock so others lookups can proceed
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c.mutex.RUnlock()
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// really not there, try to build it
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newItem, err := build(typ, config, cache)
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if err != nil {
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return nil, err
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}
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// now we've built it, acquire lock
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c.mutex.Lock()
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defer c.mutex.Unlock()
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// check again because it could have been created while trading locks
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_, cached = c.data[name]
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if cached {
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return nil, ErrAlreadyDefined
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}
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c.data[name] = newItem
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return newItem, nil
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}
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