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sequence.go
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sequence.go
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package kvstore
import (
"encoding/binary"
"sync"
"github.com/iotaledger/hive.go/ierrors"
)
// Sequence represents a simple integer sequence backed by a KVStore.
// A Sequence can be used to get a list of monotonically increasing integers.
type Sequence struct {
sync.Mutex
store KVStore
key []byte
interval uint64 // the interval in which numbers are backed by the store
next uint64 // next number to be returned
reserved uint64 // until which number is reserved in the store
}
// NewSequence initiates a new sequence object backed by the provided store.
// The interval value defines how many Next() requests can be served from memory without an access to the store.
// Multiple sequences can be created by providing different keys.
func NewSequence(store KVStore, key []byte, interval uint64) (*Sequence, error) {
if interval == 0 {
panic("interval must be greater than zero")
}
seq := &Sequence{
store: store,
key: key,
next: 0,
reserved: 0,
interval: interval,
}
return seq, nil
}
// Next returns the next integer in the sequence.
func (seq *Sequence) Next() (uint64, error) {
seq.Lock()
defer seq.Unlock()
if seq.next >= seq.reserved {
if err := seq.update(); err != nil {
return 0, err
}
}
val := seq.next
seq.next++
return val, nil
}
// Release the leased sequence to avoid wasted integers.
func (seq *Sequence) Release() error {
seq.Lock()
defer seq.Unlock()
var buf [8]byte
binary.BigEndian.PutUint64(buf[:], seq.next)
if err := seq.store.Set(seq.key, buf[:]); err != nil {
return err
}
seq.reserved = seq.next
return nil
}
func (seq *Sequence) update() error {
value, err := seq.store.Get(seq.key)
switch {
case ierrors.Is(err, ErrKeyNotFound):
seq.next = 0
case err != nil:
return err
default:
num := binary.BigEndian.Uint64(value)
seq.next = num
}
// reserve the interval and set in store
reserved := seq.next + seq.interval
var buf [8]byte
binary.BigEndian.PutUint64(buf[:], reserved)
err = seq.store.Set(seq.key, buf[:])
if err != nil {
return err
}
seq.reserved = reserved
return nil
}