动手实现一个localcache - 实现篇

// ICache abstract interface
type ICache interface {
 // Set value use default expire time. default does not expire.
 Set(key string, value []byte) error
 // Get value if find it. if value already expire will delete.
 Get(key string) ([]byte, error)
 // SetWithTime set value with expire time
 SetWithTime(key string, value []byte, expired time.Duration) error
 // Delete manual removes the key
 Delete(key string) error
 // Len computes number of entries in cache
 Len() int
 // Capacity returns amount of bytes store in the cache.
 Capacity() int
 // Close is used to signal a shutdown of the cache when you are done with it.
 // This allows the cleaning goroutines to exit and ensures references are not
 // kept to the cache preventing GC of the entire cache.
 Close() error
 // Stats returns cache's statistics
 Stats() Stats
 // GetKeyHit returns key hit
 GetKeyHit(key string) int64
}

type cache struct {
 // hashFunc represents used hash func
 hashFunc HashFunc
 // bucketCount represents the number of segments within a cache instance. value must be a power of two.
 bucketCount uint64
 // bucketMask is bitwise AND applied to the hashVal to find the segment id.
 bucketMask uint64
 // segment is shard
 segments []*segment
 // segment lock
 locks    []sync.RWMutex
 // close cache
 close chan struct{}
}

// NewCache constructor cache instance
func NewCache(opts ...Opt) (ICache, error) {
 options := &options{
  hashFunc: NewDefaultHashFunc(),
  bucketCount: defaultBucketCount,
  maxBytes: defaultMaxBytes,
  cleanTime: defaultCleanTIme,
  statsEnabled: defaultStatsEnabled,
  cleanupEnabled: defaultCleanupEnabled,
 }
 for _, each := range opts{
  each(options)
 }

 if !isPowerOfTwo(options.bucketCount){
  return nil, errShardCount
 }

  if options.maxBytes <= 0 {
  return nil, ErrBytes
 }
  
 segments := make([]*segment, options.bucketCount)
 locks := make([]sync.RWMutex, options.bucketCount)

 maxSegmentBytes := (options.maxBytes + options.bucketCount - 1) / options.bucketCount
 for index := range segments{
  segments[index] = newSegment(maxSegmentBytes, options.statsEnabled)
 }

 c := &cache{
  hashFunc: options.hashFunc,
  bucketCount: options.bucketCount,
  bucketMask: options.bucketCount - 1,
  segments: segments,
  locks: locks,
  close: make(chan struct{}),
 }
    if options.cleanupEnabled {
  go c.cleanup(options.cleanTime)
 }
 
 return c, nil
}

type segment struct {
 hashmap map[uint64]uint32
 entries buffer.IBuffer
 clock   clock
 evictList  *list.List
 stats IStats
}

func newSegment(bytes uint64, statsEnabled bool) *segment {
 if bytes == 0 {
  panic(fmt.Errorf("bytes cannot be zero"))
 }
 if bytes >= maxSegmentSize{
  panic(fmt.Errorf("too big bytes=%d; should be smaller than %d", bytes, maxSegmentSize))
 }
 capacity := (bytes + segmentSize - 1) / segmentSize
 entries := buffer.NewBuffer(int(capacity))
 entries.Reset()
 return &segment{
  entries: entries,
  hashmap: make(map[uint64]uint32),
  clock:   &systemClock{},
  evictList: list.New(),
  stats: newStats(statsEnabled),
 }
}

type Buffer struct {
 array [][]byte
 capacity int
 index int
 // maxCount = capacity - 1
 count int
 // availableSpace If any objects are removed after the buffer is full, the idle index is logged.
 // Avoid array "wormhole"
 availableSpace map[int]struct{}
 // placeholder record the index that buffer has stored.
 placeholder map[int]struct{}
}

func (c *cache) Set(key string, value []byte) error  {
 hashKey := c.hashFunc.Sum64(key)
 bucketIndex := hashKey&c.bucketMask
 c.locks[bucketIndex].Lock()
 defer c.locks[bucketIndex].Unlock()
 err := c.segments[bucketIndex].set(key, hashKey, value, defaultExpireTime)
 return err
}

func (s *segment) set(key string, hashKey uint64, value []byte, expireTime time.Duration) error {
 if expireTime <= 0{
  return ErrExpireTimeInvalid
 }
 expireAt := uint64(s.clock.Epoch(expireTime))

 if previousIndex, ok := s.hashmap[hashKey]; ok {
  if err := s.entries.Remove(int(previousIndex)); err != nil{
   return err
  }
  delete(s.hashmap, hashKey)
 }

 entry := wrapEntry(expireAt, key, hashKey, value)
 for {
  index, err := s.entries.Push(entry)
  if err == nil {
   s.hashmap[hashKey] = uint32(index)
   s.evictList.PushFront(index)
   return nil
  }
  ele := s.evictList.Back()
  if err := s.entries.Remove(ele.Value.(int)); err != nil{
   return err
  }
  s.evictList.Remove(ele)
 }
}

func (c *cache) Get(key string) ([]byte, error)  {
 hashKey := c.hashFunc.Sum64(key)
 bucketIndex := hashKey&c.bucketMask
 c.locks[bucketIndex].RLock()
 defer c.locks[hashKey&c.bucketMask].RUnlock()
 entry, err := c.segments[bucketIndex].get(key, hashKey)
 if err != nil{
  return nil, err
 }
 return entry,nil
}

func (s *segment) getWarpEntry(key string, hashKey uint64) ([]byte,error) {
 index, ok := s.hashmap[hashKey]
 if !ok {
  s.stats.miss()
  return nil, ErrEntryNotFound
 }
 entry, err := s.entries.Get(int(index))
 if err != nil{
  s.stats.miss()
  return nil, err
 }
 if entry == nil{
  s.stats.miss()
  return nil, ErrEntryNotFound
 }

 if entryKey := readKeyFromEntry(entry); key != entryKey {
  s.stats.collision()
  return nil, ErrEntryNotFound
 }
 return entry, nil
}

func (s *segment) get(key string, hashKey uint64) ([]byte, error) {
 currentTimestamp := s.clock.TimeStamp()
 entry, err := s.getWarpEntry(key, hashKey)
 if err != nil{
  return nil, err
 }
 res := readEntry(entry)

 expireAt := int64(readExpireAtFromEntry(entry))
 if currentTimestamp - expireAt >= 0{
  _ = s.entries.Remove(int(s.hashmap[hashKey]))
  delete(s.hashmap, hashKey)
  return nil, ErrEntryNotFound
 }
 s.stats.hit(key)

 return res, nil
}

func (h *cacheTestSuite) TestSetAndGet() {
 cache, err := NewCache()
 assert.Equal(h.T(), nil, err)
 key := "asong"
 value := []byte("公众号：Golang梦工厂")

 err = cache.Set(key, value)
 assert.Equal(h.T(), nil, err)

 res, err := cache.Get(key)
 assert.Equal(h.T(), nil, err)
 assert.Equal(h.T(), value, res)
 h.T().Logf("get value is %s", string(res))
}

=== RUN   TestCacheTestSuite
=== RUN   TestCacheTestSuite/TestSetAndGet
    cache_test.go:33: get value is 公众号：Golang梦工厂
--- PASS: TestCacheTestSuite (0.00s)
    --- PASS: TestCacheTestSuite/TestSetAndGet (0.00s)
PASS