mirror of
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78 lines
2 KiB
Go
78 lines
2 KiB
Go
// Copyright 2018 The Hugo Authors. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// 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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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package namedmemcache provides a memory cache with a named lock. This is suitable
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// for situations where creating the cached resource can be time consuming or otherwise
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// resource hungry, or in situations where a "once only per key" is a requirement.
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package namedmemcache
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import (
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"sync"
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"github.com/BurntSushi/locker"
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)
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// Cache holds the cached values.
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type Cache struct {
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nlocker *locker.Locker
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cache map[string]cacheEntry
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mu sync.RWMutex
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}
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type cacheEntry struct {
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value interface{}
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err error
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}
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// New creates a new cache.
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func New() *Cache {
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return &Cache{
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nlocker: locker.NewLocker(),
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cache: make(map[string]cacheEntry),
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}
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}
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// Clear clears the cache state.
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func (c *Cache) Clear() {
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c.mu.Lock()
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defer c.mu.Unlock()
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c.cache = make(map[string]cacheEntry)
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c.nlocker = locker.NewLocker()
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}
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// GetOrCreate tries to get the value with the given cache key, if not found
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// create will be called and cached.
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// This method is thread safe. It also guarantees that the create func for a given
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// key is invoced only once for this cache.
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func (c *Cache) GetOrCreate(key string, create func() (interface{}, error)) (interface{}, error) {
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c.mu.RLock()
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entry, found := c.cache[key]
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c.mu.RUnlock()
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if found {
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return entry.value, entry.err
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}
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c.nlocker.Lock(key)
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defer c.nlocker.Unlock(key)
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// Create it.
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value, err := create()
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c.mu.Lock()
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c.cache[key] = cacheEntry{value: value, err: err}
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c.mu.Unlock()
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return value, err
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}
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