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// Copyright 2019 Lunny Xiao. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package levelqueue
import (
"bytes"
"encoding/binary"
"sync"
"github.com/syndtr/goleveldb/leveldb"
)
// Queue defines a queue struct
type Queue struct {
db *leveldb.DB
highLock sync.Mutex
lowLock sync.Mutex
low int64
high int64
}
// Open opens a queue object or create it if not exist
func Open(dataDir string) (*Queue, error) {
db, err := leveldb.OpenFile(dataDir, nil)
if err != nil {
return nil, err
}
var queue = &Queue{
db: db,
}
queue.low, err = queue.readID(lowKey)
if err == leveldb.ErrNotFound {
queue.low = 1
err = db.Put(lowKey, id2bytes(1), nil)
}
if err != nil {
return nil, err
}
queue.high, err = queue.readID(highKey)
if err == leveldb.ErrNotFound {
err = db.Put(highKey, id2bytes(0), nil)
}
if err != nil {
return nil, err
}
return queue, nil
}
func (queue *Queue) readID(key []byte) (int64, error) {
bs, err := queue.db.Get(key, nil)
if err != nil {
return 0, err
}
return bytes2id(bs)
}
var (
lowKey = []byte("low")
highKey = []byte("high")
)
func (queue *Queue) highincrement() (int64, error) {
id := queue.high + 1
queue.high = id
err := queue.db.Put(highKey, id2bytes(queue.high), nil)
if err != nil {
queue.high = queue.high - 1
return 0, err
}
return id, nil
}
func (queue *Queue) highdecrement() (int64, error) {
queue.high = queue.high - 1
err := queue.db.Put(highKey, id2bytes(queue.high), nil)
if err != nil {
queue.high = queue.high + 1
return 0, err
}
return queue.high, nil
}
func (queue *Queue) lowincrement() (int64, error) {
queue.low = queue.low + 1
err := queue.db.Put(lowKey, id2bytes(queue.low), nil)
if err != nil {
queue.low = queue.low - 1
return 0, err
}
return queue.low, nil
}
func (queue *Queue) lowdecrement() (int64, error) {
queue.low = queue.low - 1
err := queue.db.Put(lowKey, id2bytes(queue.low), nil)
if err != nil {
queue.low = queue.low + 1
return 0, err
}
return queue.low, nil
}
// Len returns the length of the queue
func (queue *Queue) Len() int64 {
queue.lowLock.Lock()
queue.highLock.Lock()
l := queue.high - queue.low + 1
queue.highLock.Unlock()
queue.lowLock.Unlock()
return l
}
func id2bytes(id int64) []byte {
var buf = make([]byte, 8)
binary.PutVarint(buf, id)
return buf
}
func bytes2id(b []byte) (int64, error) {
return binary.ReadVarint(bytes.NewReader(b))
}
// RPush pushes a data from right of queue
func (queue *Queue) RPush(data []byte) error {
queue.highLock.Lock()
id, err := queue.highincrement()
if err != nil {
queue.highLock.Unlock()
return err
}
err = queue.db.Put(id2bytes(id), data, nil)
queue.highLock.Unlock()
return err
}
// LPush pushes a data from left of queue
func (queue *Queue) LPush(data []byte) error {
queue.highLock.Lock()
id, err := queue.lowdecrement()
if err != nil {
queue.highLock.Unlock()
return err
}
err = queue.db.Put(id2bytes(id), data, nil)
queue.highLock.Unlock()
return err
}
// RPop pop a data from right of queue
func (queue *Queue) RPop() ([]byte, error) {
queue.highLock.Lock()
currentID := queue.high
res, err := queue.db.Get(id2bytes(currentID), nil)
if err != nil {
queue.highLock.Unlock()
if err == leveldb.ErrNotFound {
return nil, ErrNotFound
}
return nil, err
}
_, err = queue.highdecrement()
if err != nil {
queue.highLock.Unlock()
return nil, err
}
err = queue.db.Delete(id2bytes(currentID), nil)
queue.highLock.Unlock()
if err != nil {
return nil, err
}
return res, nil
}
// LPop pop a data from left of queue
func (queue *Queue) LPop() ([]byte, error) {
queue.lowLock.Lock()
currentID := queue.low
res, err := queue.db.Get(id2bytes(currentID), nil)
if err != nil {
queue.lowLock.Unlock()
if err == leveldb.ErrNotFound {
return nil, ErrNotFound
}
return nil, err
}
_, err = queue.lowincrement()
if err != nil {
return nil, err
}
err = queue.db.Delete(id2bytes(currentID), nil)
queue.lowLock.Unlock()
if err != nil {
return nil, err
}
return res, nil
}
// Close closes the queue
func (queue *Queue) Close() error {
err := queue.db.Close()
queue.db = nil
return err
}
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