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linkeddb.go
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linkeddb.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package linkeddb
import (
"sync"
"golang.org/x/exp/maps"
"golang.org/x/exp/slices"
"github.com/ava-labs/avalanchego/cache"
"github.com/ava-labs/avalanchego/database"
)
const (
defaultCacheSize = 1024
)
var (
headKey = []byte{0x01}
_ LinkedDB = (*linkedDB)(nil)
_ database.Iterator = (*iterator)(nil)
)
// LinkedDB provides a key value interface while allowing iteration.
type LinkedDB interface {
database.KeyValueReaderWriterDeleter
IsEmpty() (bool, error)
HeadKey() ([]byte, error)
Head() (key []byte, value []byte, err error)
NewIterator() database.Iterator
NewIteratorWithStart(start []byte) database.Iterator
}
type linkedDB struct {
// lock ensure that this data structure handles its thread safety correctly.
lock sync.RWMutex
cacheLock sync.Mutex
// these variables provide caching for the head key.
headKeyIsSynced, headKeyExists, headKeyIsUpdated, updatedHeadKeyExists bool
headKey, updatedHeadKey []byte
// these variables provide caching for the nodes.
nodeCache cache.Cacher[string, *node] // key -> *node
updatedNodes map[string]*node
// db is the underlying database that this list is stored in.
db database.Database
// batch writes to [db] atomically.
batch database.Batch
}
type node struct {
Value []byte `serialize:"true"`
HasNext bool `serialize:"true"`
Next []byte `serialize:"true"`
HasPrevious bool `serialize:"true"`
Previous []byte `serialize:"true"`
}
func New(db database.Database, cacheSize int) LinkedDB {
return &linkedDB{
nodeCache: &cache.LRU[string, *node]{Size: cacheSize},
updatedNodes: make(map[string]*node),
db: db,
batch: db.NewBatch(),
}
}
func NewDefault(db database.Database) LinkedDB {
return New(db, defaultCacheSize)
}
func (ldb *linkedDB) Has(key []byte) (bool, error) {
ldb.lock.RLock()
defer ldb.lock.RUnlock()
return ldb.db.Has(nodeKey(key))
}
func (ldb *linkedDB) Get(key []byte) ([]byte, error) {
ldb.lock.RLock()
defer ldb.lock.RUnlock()
node, err := ldb.getNode(key)
return node.Value, err
}
func (ldb *linkedDB) Put(key, value []byte) error {
ldb.lock.Lock()
defer ldb.lock.Unlock()
ldb.resetBatch()
// If the key already has a node in the list, update that node.
existingNode, err := ldb.getNode(key)
if err == nil {
existingNode.Value = slices.Clone(value)
if err := ldb.putNode(key, existingNode); err != nil {
return err
}
return ldb.writeBatch()
}
if err != database.ErrNotFound {
return err
}
// The key isn't currently in the list, so we should add it as the head.
newHead := node{Value: slices.Clone(value)}
if headKey, err := ldb.getHeadKey(); err == nil {
// The list currently has a head, so we need to update the old head.
oldHead, err := ldb.getNode(headKey)
if err != nil {
return err
}
oldHead.HasPrevious = true
oldHead.Previous = key
if err := ldb.putNode(headKey, oldHead); err != nil {
return err
}
newHead.HasNext = true
newHead.Next = headKey
} else if err != database.ErrNotFound {
return err
}
if err := ldb.putNode(key, newHead); err != nil {
return err
}
if err := ldb.putHeadKey(key); err != nil {
return err
}
return ldb.writeBatch()
}
func (ldb *linkedDB) Delete(key []byte) error {
ldb.lock.Lock()
defer ldb.lock.Unlock()
currentNode, err := ldb.getNode(key)
if err == database.ErrNotFound {
return nil
}
if err != nil {
return err
}
ldb.resetBatch()
// We're trying to delete this node.
if err := ldb.deleteNode(key); err != nil {
return err
}
switch {
case currentNode.HasPrevious:
// We aren't modifying the head.
previousNode, err := ldb.getNode(currentNode.Previous)
if err != nil {
return err
}
previousNode.HasNext = currentNode.HasNext
previousNode.Next = currentNode.Next
if err := ldb.putNode(currentNode.Previous, previousNode); err != nil {
return err
}
if currentNode.HasNext {
// We aren't modifying the tail.
nextNode, err := ldb.getNode(currentNode.Next)
if err != nil {
return err
}
nextNode.HasPrevious = true
nextNode.Previous = currentNode.Previous
if err := ldb.putNode(currentNode.Next, nextNode); err != nil {
return err
}
}
case !currentNode.HasNext:
// This is the only node, so we don't have a head anymore.
if err := ldb.deleteHeadKey(); err != nil {
return err
}
default:
// The next node will be the new head.
if err := ldb.putHeadKey(currentNode.Next); err != nil {
return err
}
nextNode, err := ldb.getNode(currentNode.Next)
if err != nil {
return err
}
nextNode.HasPrevious = false
nextNode.Previous = nil
if err := ldb.putNode(currentNode.Next, nextNode); err != nil {
return err
}
}
return ldb.writeBatch()
}
func (ldb *linkedDB) IsEmpty() (bool, error) {
_, err := ldb.HeadKey()
if err == database.ErrNotFound {
return true, nil
}
return false, err
}
func (ldb *linkedDB) HeadKey() ([]byte, error) {
ldb.lock.RLock()
defer ldb.lock.RUnlock()
return ldb.getHeadKey()
}
func (ldb *linkedDB) Head() ([]byte, []byte, error) {
ldb.lock.RLock()
defer ldb.lock.RUnlock()
headKey, err := ldb.getHeadKey()
if err != nil {
return nil, nil, err
}
head, err := ldb.getNode(headKey)
return headKey, head.Value, err
}
// This iterator does not guarantee that keys are returned in lexicographic
// order.
func (ldb *linkedDB) NewIterator() database.Iterator {
return &iterator{ldb: ldb}
}
// NewIteratorWithStart returns an iterator that starts at [start].
// This iterator does not guarantee that keys are returned in lexicographic
// order.
// If [start] is not in the list, starts iterating from the list head.
func (ldb *linkedDB) NewIteratorWithStart(start []byte) database.Iterator {
hasStartKey, err := ldb.Has(start)
if err == nil && hasStartKey {
return &iterator{
ldb: ldb,
initialized: true,
nextKey: start,
}
}
// If the start key isn't present, start from the head
return ldb.NewIterator()
}
func (ldb *linkedDB) getHeadKey() ([]byte, error) {
// If the ldb read lock is held, then there needs to be additional
// synchronization here to avoid racy behavior.
ldb.cacheLock.Lock()
defer ldb.cacheLock.Unlock()
if ldb.headKeyIsSynced {
if ldb.headKeyExists {
return ldb.headKey, nil
}
return nil, database.ErrNotFound
}
headKey, err := ldb.db.Get(headKey)
if err == nil {
ldb.headKeyIsSynced = true
ldb.headKeyExists = true
ldb.headKey = headKey
return headKey, nil
}
if err == database.ErrNotFound {
ldb.headKeyIsSynced = true
ldb.headKeyExists = false
return nil, database.ErrNotFound
}
return headKey, err
}
func (ldb *linkedDB) putHeadKey(key []byte) error {
ldb.headKeyIsUpdated = true
ldb.updatedHeadKeyExists = true
ldb.updatedHeadKey = key
return ldb.batch.Put(headKey, key)
}
func (ldb *linkedDB) deleteHeadKey() error {
ldb.headKeyIsUpdated = true
ldb.updatedHeadKeyExists = false
return ldb.batch.Delete(headKey)
}
func (ldb *linkedDB) getNode(key []byte) (node, error) {
// If the ldb read lock is held, then there needs to be additional
// synchronization here to avoid racy behavior.
ldb.cacheLock.Lock()
defer ldb.cacheLock.Unlock()
keyStr := string(key)
if n, exists := ldb.nodeCache.Get(keyStr); exists {
if n == nil {
return node{}, database.ErrNotFound
}
return *n, nil
}
nodeBytes, err := ldb.db.Get(nodeKey(key))
if err == database.ErrNotFound {
ldb.nodeCache.Put(keyStr, nil)
return node{}, err
}
if err != nil {
return node{}, err
}
n := node{}
_, err = c.Unmarshal(nodeBytes, &n)
if err == nil {
ldb.nodeCache.Put(keyStr, &n)
}
return n, err
}
func (ldb *linkedDB) putNode(key []byte, n node) error {
ldb.updatedNodes[string(key)] = &n
nodeBytes, err := c.Marshal(codecVersion, n)
if err != nil {
return err
}
return ldb.batch.Put(nodeKey(key), nodeBytes)
}
func (ldb *linkedDB) deleteNode(key []byte) error {
ldb.updatedNodes[string(key)] = nil
return ldb.batch.Delete(nodeKey(key))
}
func (ldb *linkedDB) resetBatch() {
ldb.headKeyIsUpdated = false
maps.Clear(ldb.updatedNodes)
ldb.batch.Reset()
}
func (ldb *linkedDB) writeBatch() error {
if err := ldb.batch.Write(); err != nil {
return err
}
if ldb.headKeyIsUpdated {
ldb.headKeyIsSynced = true
ldb.headKeyExists = ldb.updatedHeadKeyExists
ldb.headKey = ldb.updatedHeadKey
}
for key, n := range ldb.updatedNodes {
ldb.nodeCache.Put(key, n)
}
return nil
}
type iterator struct {
ldb *linkedDB
initialized, exhausted bool
key, value, nextKey []byte
err error
}
func (it *iterator) Next() bool {
// If the iterator has been exhausted, there is no next value.
if it.exhausted {
it.key = nil
it.value = nil
return false
}
it.ldb.lock.RLock()
defer it.ldb.lock.RUnlock()
// If the iterator was not yet initialized, do it now.
if !it.initialized {
it.initialized = true
headKey, err := it.ldb.getHeadKey()
if err == database.ErrNotFound {
it.exhausted = true
it.key = nil
it.value = nil
return false
}
if err != nil {
it.exhausted = true
it.key = nil
it.value = nil
it.err = err
return false
}
it.nextKey = headKey
}
nextNode, err := it.ldb.getNode(it.nextKey)
if err == database.ErrNotFound {
it.exhausted = true
it.key = nil
it.value = nil
return false
}
if err != nil {
it.exhausted = true
it.key = nil
it.value = nil
it.err = err
return false
}
it.key = it.nextKey
it.value = nextNode.Value
it.nextKey = nextNode.Next
it.exhausted = !nextNode.HasNext
return true
}
func (it *iterator) Error() error {
return it.err
}
func (it *iterator) Key() []byte {
return it.key
}
func (it *iterator) Value() []byte {
return it.value
}
func (*iterator) Release() {}
func nodeKey(key []byte) []byte {
newKey := make([]byte, len(key)+1)
copy(newKey[1:], key)
return newKey
}