/
pqueue.go
227 lines (210 loc) · 5.4 KB
/
pqueue.go
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package boltqueue
import (
"encoding/binary"
"errors"
"fmt"
"io"
"github.com/coreos/bbolt"
)
// TODO: Interfacification of messages
var (
foundItem = errors.New("item found")
)
// PQueue is a priority queue backed by a Bolt database on disk
type PQueue struct {
conn *bolt.DB
}
// NewPQueue consumes an existing opened *bold.DB.
func NewPQueue(db *bolt.DB) *PQueue {
b := &PQueue{
conn: db,
}
return b
}
// NewPQueueFromFile loads or creates a new PQueue with the given filename
func NewPQueueFromFile(filename string) (*PQueue, error) {
db, err := bolt.Open(filename, 0600, nil)
if err != nil {
return nil, err
}
b := &PQueue{
conn: db,
}
return b, nil
}
// Enqueue adds a message to the queue
func (b *PQueue) Enqueue(topic string, priority int, messages ...*Message) error {
if priority < 0 || priority > 255 {
return fmt.Errorf("Invalid priority %d on Enqueue", priority)
}
p := append([]byte(topic), byte(uint8(priority)))
return b.conn.Update(func(tx *bolt.Tx) error {
// Get bucket for this priority level
pb, err := tx.CreateBucketIfNotExists(p)
if err != nil {
return err
}
for _, message := range messages {
if message.Key == 0 {
id, err := pb.NextSequence()
if err != nil {
return err
}
message.Key = id
}
key := make([]byte, binary.MaxVarintLen64)
binary.BigEndian.PutUint64(key, message.Key)
if err = pb.Put(key, message.Value); err != nil {
return err
}
}
return nil
})
}
// Requeue adds a message back into the queue, keeping its precedence.
// If added at the same priority, it should be among the first to dequeue.
// If added at a different priority, it will dequeue before newer messages
// of that priority.
func (b *PQueue) Requeue(topic string, priority int, messages ...*Message) error {
for _, message := range messages {
if message.Key == 0 {
return fmt.Errorf("Cannot requeue new message")
}
}
return b.Enqueue(topic, priority, messages...)
}
// Dequeue removes the oldest, highest priority message from the queue and
// returns it
func (b *PQueue) Dequeue(topic string) (*Message, error) {
var m *Message
err := b.conn.Update(func(tx *bolt.Tx) error {
err := tx.ForEach(func(bname []byte, bucket *bolt.Bucket) error {
// Only operate on buckets which match topic.
btopic := string(bname)[0 : len(bname)-1]
if btopic != topic {
return nil
}
bpri := bname[len(bname)-1 : len(bname)]
cursor := bucket.Cursor()
k, v := cursor.First()
if len(v) == 0 {
return nil
}
priority, _ := binary.Uvarint(bpri)
m = &Message{
Key: binary.BigEndian.Uint64(k),
Value: cloneBytes(v),
priority: int(priority),
}
// Remove message.
if err := cursor.Delete(); err != nil {
return err
}
return foundItem // To stop iteration.
})
if err != nil && err != foundItem {
return err
}
return nil
})
if err != nil {
return nil, err
}
if m == nil {
return nil, io.EOF
}
return m, nil
}
// Scan invokes a callback on each message in a topic.
func (b *PQueue) Scan(topic string, fn func(m *Message)) error {
return b.conn.View(func(tx *bolt.Tx) error {
return tx.ForEach(func(bname []byte, bucket *bolt.Bucket) error {
// Only operate on buckets which match topic.
btopic := string(bname)[0 : len(bname)-1]
if btopic != topic {
return nil
}
bpri := bname[len(bname)-1 : len(bname)]
cursor := bucket.Cursor()
for k, v := cursor.First(); len(v) > 0; k, v = cursor.Next() {
if len(v) == 0 {
return nil
}
priority, _ := binary.Uvarint(bpri)
m := &Message{
Key: binary.BigEndian.Uint64(k),
Value: cloneBytes(v),
priority: int(priority),
}
fn(m)
}
return nil
})
})
}
// ScanWithBreak invokes a callback on each message in a topic as long as the callback
// returns true.
func (b *PQueue) ScanWithBreak(topic string, fn func(m *Message) bool) error {
keepGoing := true
return b.conn.View(func(tx *bolt.Tx) error {
return tx.ForEach(func(bname []byte, bucket *bolt.Bucket) error {
if !keepGoing {
return nil
}
// Only operate on buckets which match topic.
btopic := string(bname)[0 : len(bname)-1]
if btopic != topic {
return nil
}
bpri := bname[len(bname)-1 : len(bname)]
cursor := bucket.Cursor()
for k, v := cursor.First(); len(v) > 0; k, v = cursor.Next() {
if len(v) == 0 {
return nil
}
priority, _ := binary.Uvarint(bpri)
m := &Message{
Key: binary.BigEndian.Uint64(k),
Value: cloneBytes(v),
priority: int(priority),
}
if keepGoing = fn(m); !keepGoing {
break
}
}
return nil
})
})
}
// Len returns the number of entries of a given priority from 1 to 5.
func (b *PQueue) Len(topic string, priority int) (int, error) {
if priority < 0 || priority > 255 {
return 0, fmt.Errorf("Invalid priority %d for Size()", priority)
}
tx, err := b.conn.Begin(false)
if err != nil {
return 0, err
}
defer tx.Rollback()
btopic := append([]byte(topic), byte(uint8(priority)))
bucket := tx.Bucket(btopic)
if bucket == nil {
return 0, nil
}
count := bucket.Stats().KeyN
return count, nil
}
// Close closes the queue and releases all resources
func (b *PQueue) Close() error {
err := b.conn.Close()
if err != nil {
return err
}
return nil
}
// cloneBytes was taken from boltDB. Avoids corruption when re-queueing.
func cloneBytes(v []byte) []byte {
var clone = make([]byte, len(v))
copy(clone, v)
return clone
}