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query_conversion_lru.go
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query_conversion_lru.go
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// Copyright (c) 2019 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package storage
import (
"container/list"
"fmt"
"github.com/m3db/m3/src/m3ninx/idx"
)
// QueryConversionLRU implements a fixed size LRU cache
type QueryConversionLRU struct {
size int
evictList *list.List
items map[string]*list.Element
}
// entry is used to hold a value in the evictList
type entry struct {
key []byte
value idx.Query
}
// NewQueryConversionLRU constructs an LRU of the given size
func NewQueryConversionLRU(size int) (*QueryConversionLRU, error) {
if size <= 0 {
return nil, fmt.Errorf("must provide a positive size, instead got: %d", size)
}
c := &QueryConversionLRU{
size: size,
evictList: list.New(),
items: make(map[string]*list.Element, size),
}
return c, nil
}
// Set adds a value to the cache. Returns true if an eviction occurred.
func (c *QueryConversionLRU) Set(key []byte, value idx.Query) (evicted bool) {
// Check for existing item
if ent, ok := c.items[string(key)]; ok {
c.evictList.MoveToFront(ent)
ent.Value.(*entry).value = value
return false
}
// Add new item
ent := &entry{key, value}
entry := c.evictList.PushFront(ent)
c.items[string(key)] = entry
evict := c.evictList.Len() > c.size
// Verify size not exceeded
if evict {
c.removeOldest()
}
return evict
}
// Get looks up a key's value from the cache.
func (c *QueryConversionLRU) Get(key []byte) (value idx.Query, ok bool) {
if ent, ok := c.items[string(key)]; ok {
c.evictList.MoveToFront(ent)
return ent.Value.(*entry).value, true
}
return
}
// removeOldest removes the oldest item from the cache.
func (c *QueryConversionLRU) removeOldest() {
ent := c.evictList.Back()
if ent != nil {
c.removeElement(ent)
}
}
// removeElement is used to remove a given list element from the cache
func (c *QueryConversionLRU) removeElement(e *list.Element) {
c.evictList.Remove(e)
kv := e.Value.(*entry)
delete(c.items, string(kv.key))
}