cubefs

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// Copyright 2018 The CubeFS Authors.
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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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//
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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
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// implied. See the License for the specific language governing
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// permissions and limitations under the License.
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package storage
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import (
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	"container/list"
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	"sync"
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)
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// ExtentMapItem stores the extent entity pointer and the element
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// pointer of the extent entity in a cache list.
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type ExtentMapItem struct {
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	e       *Extent
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	element *list.Element
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}
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// ExtentCache is an implementation of the ExtentCache with LRU support.
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type ExtentCache struct {
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	extentMap   map[uint64]*ExtentMapItem
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	extentList  *list.List
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	tinyExtents map[uint64]*Extent
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	tinyLock    sync.RWMutex
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	lock        sync.RWMutex
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	capacity    int
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}
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// NewExtentCache creates and returns a new ExtentCache instance.
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func NewExtentCache(capacity int) *ExtentCache {
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	return &ExtentCache{
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		extentMap:   make(map[uint64]*ExtentMapItem),
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		extentList:  list.New(),
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		capacity:    capacity,
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		tinyExtents: make(map[uint64]*Extent),
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	}
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}
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// Put puts an extent object into the cache.
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func (cache *ExtentCache) Put(e *Extent) {
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	if IsTinyExtent(e.extentID) {
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		cache.tinyLock.Lock()
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		cache.tinyExtents[e.extentID] = e
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		cache.tinyLock.Unlock()
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		return
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	}
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	cache.lock.Lock()
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	defer cache.lock.Unlock()
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	item := &ExtentMapItem{
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		e:       e,
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		element: cache.extentList.PushBack(e),
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	}
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	cache.extentMap[e.extentID] = item
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	cache.evict()
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}
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// Get gets the extent from the cache.
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func (cache *ExtentCache) Get(extentID uint64) (e *Extent, ok bool) {
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	if IsTinyExtent(extentID) {
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		cache.tinyLock.RLock()
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		e, ok = cache.tinyExtents[extentID]
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		cache.tinyLock.RUnlock()
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		return
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	}
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	cache.lock.Lock()
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	defer cache.lock.Unlock()
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	var item *ExtentMapItem
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	if item, ok = cache.extentMap[extentID]; ok {
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		if !IsTinyExtent(extentID) {
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			cache.extentList.MoveToBack(item.element)
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		}
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		e = item.e
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	}
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	return
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}
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// Del deletes the extent stored in the cache.
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func (cache *ExtentCache) Del(extentID uint64) {
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	if IsTinyExtent(extentID) {
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		return
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	}
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	cache.lock.Lock()
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	defer cache.lock.Unlock()
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	var (
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		item *ExtentMapItem
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		ok   bool
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	)
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	if item, ok = cache.extentMap[extentID]; ok {
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		delete(cache.extentMap, extentID)
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		cache.extentList.Remove(item.element)
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		item.e.Close()
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	}
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}
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// Clear closes all the extents stored in the cache.
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func (cache *ExtentCache) Clear() {
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	cache.tinyLock.RLock()
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	for _, extent := range cache.tinyExtents {
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		extent.Close()
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	}
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	cache.tinyLock.RUnlock()
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	cache.lock.Lock()
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	defer cache.lock.Unlock()
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	for e := cache.extentList.Front(); e != nil; {
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		curr := e
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		e = e.Next()
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		ec := curr.Value.(*Extent)
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		delete(cache.extentMap, ec.extentID)
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		ec.Close()
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		cache.extentList.Remove(curr)
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	}
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	cache.extentList = list.New()
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	cache.extentMap = make(map[uint64]*ExtentMapItem)
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}
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// Size returns number of extents stored in the cache.
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func (cache *ExtentCache) Size() int {
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	cache.lock.RLock()
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	defer cache.lock.RUnlock()
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	return cache.extentList.Len()
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}
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func (cache *ExtentCache) evict() {
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	if cache.capacity <= 0 {
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		return
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	}
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	needRemove := cache.extentList.Len() - cache.capacity
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	for i := 0; i < needRemove; i++ {
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		if e := cache.extentList.Front(); e != nil {
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			front := e.Value.(*Extent)
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			if IsTinyExtent(front.extentID) {
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				continue
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			}
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			delete(cache.extentMap, front.extentID)
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			cache.extentList.Remove(e)
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			front.Close()
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		}
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	}
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}
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// Flush synchronizes the extent stored in the cache to the disk.
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func (cache *ExtentCache) Flush() {
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	cache.tinyLock.RLock()
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	for _, extent := range cache.tinyExtents {
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		extent.Flush()
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	}
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	cache.tinyLock.RUnlock()
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	cache.lock.RLock()
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	defer cache.lock.RUnlock()
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	for _, item := range cache.extentMap {
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		item.e.Flush()
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	}
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}
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