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cache.go
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cache.go
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package store
import (
"bytes"
"errors"
"io"
"mime/multipart"
)
type cache struct {
data map[string][]byte //图片缓存
keyList []string //按照时间顺序排列的图片KEY列表
useSize int64 //缓存已用空间
maxSize int64 //最大缓存
}
var gCache cache
func computeSize(keyLen, dataLen int) int {
//map 中每个项额外占用大概10.79字节,此处取11表示
const extraLen = 11
return keyLen*2 + dataLen + extraLen
}
//准备cache空间,注意此函数仅在逻辑上释放已占用空间,真正的内存回收依赖Golang的GC
func (c *cache) prepare(expectLen int) error {
//请求空间超出能力
if c.maxSize < int64(expectLen) {
return errors.New("缓存空间不足")
}
//剩余空间充足
if c.maxSize-c.useSize >= int64(expectLen) {
return nil
}
//释放空间
var releaseLen int
var releaseNum int
for _, key := range c.keyList {
releaseLen = releaseLen + computeSize(len(key), len(c.data[key]))
delete(c.data, key)
releaseNum = releaseNum + 1
if releaseLen >= expectLen {
break
}
}
c.keyList = c.keyList[releaseNum:]
c.useSize = c.useSize - int64(releaseLen)
return nil
}
func (c *cache) write(f multipart.File, md5 string, name string) error {
//此处必须Seek回起点,否则copy不到东西
_, err := f.Seek(0, 0)
if err != nil {
return err
}
//文件写入内存
var buf bytes.Buffer
_, err = io.Copy(&buf, f)
if err != nil {
return err
}
//准备缓存空间
key := md5 + name
err = c.prepare(computeSize(len(key), buf.Len()))
if err != nil {
return err
}
//写入缓存
c.derectWrite(key, buf.Bytes())
return nil
}
func (c *cache) derectWrite(key string, data []byte) {
c.data[key] = data
c.keyList = append(c.keyList, key)
c.useSize = c.useSize + int64(computeSize(len(key), len(data)))
}
func (c *cache) read(key string) ([]byte, error) {
if v, ok := c.data[key]; ok {
return v, nil
}
return nil, errors.New("缓存未命中")
}
func (c *cache) memWrite(key string, data []byte) error {
//准备缓存空间
err := c.prepare(computeSize(len(key), len(data)))
if err != nil {
return err
}
//写入缓存
c.derectWrite(key, data)
return nil
}
func (c cache) isEnable() bool {
return c.maxSize > 0
}