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store.go
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store.go
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package levelcache
import (
"fmt"
"os"
"path/filepath"
"sync"
"syscall"
"time"
)
const (
minBlockSize int64 = 1024 * 1024
maxBlockSize int64 = 1024 * 1024 * 1024 * 10
defaultBlockCount int64 = 1024
)
type store struct {
dir string
cap int64
size int64
blockSize int64
curOff int64
curBlock int64
lock sync.RWMutex
blocks map[int64][]byte
}
func getBlockSize(capacity int64) int64 {
// blockSize = min(max(minBlockSize, capacity / defaultBlockCount), maxBlockSize)
size := int64(capacity / defaultBlockCount)
if size < minBlockSize {
size = minBlockSize
}
if size > maxBlockSize {
size = maxBlockSize
}
return size
}
func newStore(dir string, cap int64) *store {
blockSize := getBlockSize(cap)
s := &store{
dir: dir,
cap: cap,
size: 0,
blockSize: blockSize,
curOff: blockSize,
curBlock: 0,
blocks: make(map[int64][]byte)}
blocks, err := filepath.Glob(fmt.Sprintf("%s/*.blk", dir))
success(err)
var b int64
pattern := fmt.Sprintf("%s/%d-%%d.blk", dir, version)
for _, path := range blocks {
fmt.Sscanf(path, pattern, &b)
data := s.mmap(path, 0)
s.blocks[b] = data
s.size += int64(len(data))
}
return s
}
func (s *store) get(sv *segValue) []byte {
s.lock.RLock()
defer s.lock.RUnlock()
if b, ok := s.blocks[sv.Block]; ok {
return b[sv.Off : sv.Off+int64(sv.Size)]
}
return nil
}
func (s *store) add(data []byte) (block int64, off int64) {
s.lock.Lock()
defer s.lock.Unlock()
size := int64(len(data))
if size > s.blockSize {
s.addBlock(size) // single block for big data
} else if size+s.curOff > s.blockSize {
s.addBlock(s.blockSize)
}
block = s.curBlock
off = int64(s.curOff)
copy(s.blocks[s.curBlock][s.curOff:s.curOff+size], data)
s.curOff += size
return block, off
}
func (s *store) clear() (blocks []int64) {
s.lock.Lock()
defer s.lock.Unlock()
for len(s.blocks) >= 0 && s.size > s.cap {
min, data := s.minBlock()
path := s.getPath(min)
s.size -= int64(len(data))
delete(s.blocks, min)
blocks = append(blocks, min)
success(os.Remove(path))
success(syscall.Munmap(data))
}
return blocks
}
func (s *store) close() {
s.lock.Lock()
defer s.lock.Unlock()
for _, data := range s.blocks {
syscall.Munmap(data)
}
}
func (s *store) minBlock() (min int64, data []byte) {
min = 0
for i, d := range s.blocks {
if i < min || min == 0 {
min, data = i, d
}
}
return min, data
}
func (s *store) addBlock(size int64) {
s.curBlock = time.Now().UnixNano()
s.blocks[s.curBlock] = s.mmap(s.getPath(s.curBlock), int64(s.blockSize))
s.curOff = 0
s.size += size
}
func (s *store) getPath(block int64) string {
return fmt.Sprintf("%s/%d-%016x.dat", s.dir, version, block)
}
func (s *store) mmap(path string, size int64) (data []byte) {
if size == 0 {
info, e1 := os.Stat(path)
success(e1)
size = info.Size()
}
f, e2 := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0600)
success(e2)
defer f.Close()
success(f.Truncate(size))
data, err := syscall.Mmap(int(f.Fd()), 0, int(size),
syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
success(err)
return data
}