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segment.go
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segment.go
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package bigcache
import (
"github.com/QuangTung97/bigcache/memhash"
"sync"
"sync/atomic"
"unsafe"
)
type segment struct {
mu sync.Mutex
rb ringBuf
kv map[uint32]int
getNow func() uint32
maxConsecutiveEvacuation int
totalAccessTime uint64
total uint64
accessCount uint64
hitCount uint64
_padding [18]byte // for align with cache lines
}
type entryHeader struct {
hash uint32
accessTime uint32
keyLen uint16
deleted bool
valLen uint32
valCap uint32
}
const entryHeaderSize = int(unsafe.Sizeof(entryHeader{}))
const entryHeaderAlign = int(unsafe.Alignof(entryHeader{}))
const entryHeaderAlignMask = ^uint32(entryHeaderAlign - 1)
func initSegment(s *segment, bufSize int) {
s.rb = newRingBuf(bufSize)
s.kv = map[uint32]int{}
s.getNow = getNowMono
s.maxConsecutiveEvacuation = 5
}
func getNowMono() uint32 {
return uint32(memhash.NanoTime() / 1000000000)
}
func (s *segment) put(hash uint32, key []byte, value []byte) {
var headerData [entryHeaderSize]byte
offset, existed := s.kv[hash]
if existed {
s.rb.readAt(headerData[:], offset)
header := (*entryHeader)(unsafe.Pointer(&headerData[0]))
s.totalAccessTime -= uint64(header.accessTime)
if s.keyEqual(header, offset, key) {
if len(value) <= int(header.valCap) {
s.rb.writeAt(value, offset+entryHeaderSize+int(header.keyLen))
header.valLen = uint32(len(value))
header.accessTime = s.getNow()
s.totalAccessTime += uint64(header.accessTime)
s.rb.writeAt(headerData[:], offset)
return
}
}
header.deleted = true
s.rb.writeAt(headerData[:], offset)
}
keyLen := uint16(len(key))
valLen := uint32(len(value))
totalLen := uint32(keyLen) + valLen
totalLenAligned := nextNumberAlignToHeader(totalLen)
totalSize := entryHeaderSize + int(totalLenAligned)
s.evacuate(totalSize)
header := (*entryHeader)(unsafe.Pointer(&headerData[0]))
header.hash = hash
header.accessTime = s.getNow()
header.keyLen = keyLen
header.deleted = false
header.valLen = valLen
header.valCap = totalLenAligned - uint32(keyLen)
offset = s.rb.append(headerData[:])
s.rb.append(key)
s.rb.append(value)
s.rb.appendEmpty(int(header.valCap - header.valLen))
s.kv[hash] = offset
if !existed {
atomic.AddUint64(&s.total, 1)
}
s.totalAccessTime += uint64(header.accessTime)
}
func (s *segment) evacuate(expectedSize int) {
var headerData [entryHeaderSize]byte
consecutiveEvacuation := 0
for s.rb.getAvailable() < expectedSize {
offset := s.rb.getBegin()
s.rb.readAt(headerData[:], offset)
header := (*entryHeader)(unsafe.Pointer(&headerData[0]))
size := entryHeaderSize + int(header.keyLen) + int(header.valCap)
expired := atomic.LoadUint64(&s.total)*uint64(header.accessTime) < s.totalAccessTime
if header.deleted || expired || consecutiveEvacuation >= s.maxConsecutiveEvacuation {
consecutiveEvacuation = 0
s.rb.skip(size)
if !header.deleted {
delete(s.kv, header.hash)
atomic.AddUint64(&s.total, ^uint64(0))
s.totalAccessTime -= uint64(header.accessTime)
}
} else {
prevEnd := s.rb.evacuate(size)
s.kv[header.hash] = prevEnd
consecutiveEvacuation++
}
}
}
func (s *segment) get(hash uint32, key []byte, value []byte) (n int, ok bool) {
atomic.AddUint64(&s.accessCount, 1)
offset, ok := s.kv[hash]
if !ok {
return 0, false
}
var headerData [entryHeaderSize]byte
s.rb.readAt(headerData[:], offset)
header := (*entryHeader)(unsafe.Pointer(&headerData[0]))
if !s.keyEqual(header, offset, key) {
return 0, false
}
atomic.AddUint64(&s.hitCount, 1)
readLen := int(header.valLen)
if readLen > len(value) {
readLen = len(value)
}
s.rb.readAt(value[:readLen], offset+entryHeaderSize+int(header.keyLen))
s.totalAccessTime -= uint64(header.accessTime)
header.accessTime = s.getNow()
s.rb.writeAt(headerData[:], offset)
s.totalAccessTime += uint64(header.accessTime)
return int(header.valLen), true
}
func (s *segment) delete(hash uint32, key []byte) bool {
offset, ok := s.kv[hash]
if !ok {
return false
}
var headerData [entryHeaderSize]byte
s.rb.readAt(headerData[:], offset)
header := (*entryHeader)(unsafe.Pointer(&headerData[0]))
if !s.keyEqual(header, offset, key) {
return false
}
header.deleted = true
s.rb.writeAt(headerData[:], offset)
delete(s.kv, hash)
atomic.AddUint64(&s.total, ^uint64(0))
s.totalAccessTime -= uint64(header.accessTime)
return true
}
func (s *segment) keyEqual(header *entryHeader, offset int, key []byte) bool {
if int(header.keyLen) != len(key) {
return false
}
if ok := s.rb.bytesEqual(offset+entryHeaderSize, key); !ok {
return false
}
return true
}
func (s *segment) getTotal() uint64 {
return atomic.LoadUint64(&s.total)
}
func (s *segment) getHitCount() uint64 {
return atomic.LoadUint64(&s.hitCount)
}
func (s *segment) getAccessCount() uint64 {
return atomic.LoadUint64(&s.accessCount)
}
func nextNumberAlignToHeader(n uint32) uint32 {
return (n + uint32(entryHeaderAlign) - 1) & entryHeaderAlignMask
}