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ackqueue.go
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ackqueue.go
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// Copyright (c) 2014 The SurgeMQ Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sessions
import (
"errors"
"fmt"
"math"
"sync"
"github.com/liaoliaopro/surgemq/message"
)
var (
errQueueFull error = errors.New("queue full")
errQueueEmpty error = errors.New("queue empty")
errWaitMessage error = errors.New("Invalid message to wait for ack")
errAckMessage error = errors.New("Invalid message for acking")
)
type ackmsg struct {
// Message type of the message waiting for ack
Mtype message.MessageType
// Current state of the ack-waiting message
State message.MessageType
// Packet ID of the message. Every message that require ack'ing must have a valid
// packet ID. Messages that have message I
Pktid uint16
// Slice containing the message bytes
Msgbuf []byte
// Slice containing the ack message bytes
Ackbuf []byte
// When ack cycle completes, call this function
OnComplete interface{}
}
// Ackqueue is a growing queue implemented based on a ring buffer. As the buffer
// gets full, it will auto-grow.
//
// Ackqueue is used to store messages that are waiting for acks to come back. There
// are a few scenarios in which acks are required.
// 1. Client sends SUBSCRIBE message to server, waits for SUBACK.
// 2. Client sends UNSUBSCRIBE message to server, waits for UNSUBACK.
// 3. Client sends PUBLISH QoS 1 message to server, waits for PUBACK.
// 4. Server sends PUBLISH QoS 1 message to client, waits for PUBACK.
// 5. Client sends PUBLISH QoS 2 message to server, waits for PUBREC.
// 6. Server sends PUBREC message to client, waits for PUBREL.
// 7. Client sends PUBREL message to server, waits for PUBCOMP.
// 8. Server sends PUBLISH QoS 2 message to client, waits for PUBREC.
// 9. Client sends PUBREC message to server, waits for PUBREL.
// 10. Server sends PUBREL message to client, waits for PUBCOMP.
// 11. Client sends PINGREQ message to server, waits for PINGRESP.
type Ackqueue struct {
size int64
mask int64
count int64
head int64
tail int64
ping ackmsg
ring []ackmsg
emap map[uint16]int64
ackdone []ackmsg
mu sync.Mutex
}
func newAckqueue(n int) *Ackqueue {
m := int64(n)
if !powerOfTwo64(m) {
m = roundUpPowerOfTwo64(m)
}
return &Ackqueue{
size: m,
mask: m - 1,
count: 0,
head: 0,
tail: 0,
ring: make([]ackmsg, m),
emap: make(map[uint16]int64, m),
ackdone: make([]ackmsg, 0),
}
}
// Wait() copies the message into a waiting queue, and waits for the corresponding
// ack message to be received.
func (this *Ackqueue) Wait(msg message.Message, onComplete interface{}) error {
this.mu.Lock()
defer this.mu.Unlock()
switch msg := msg.(type) {
case *message.PublishMessage:
if msg.QoS() == message.QosAtMostOnce {
//return fmt.Errorf("QoS 0 messages don't require ack")
return errWaitMessage
}
this.insert(msg.PacketId(), msg, onComplete)
case *message.SubscribeMessage:
this.insert(msg.PacketId(), msg, onComplete)
case *message.UnsubscribeMessage:
this.insert(msg.PacketId(), msg, onComplete)
case *message.PingreqMessage:
this.ping = ackmsg{
Mtype: message.PINGREQ,
State: message.RESERVED,
OnComplete: onComplete,
}
default:
return errWaitMessage
}
return nil
}
// Ack() takes the ack message supplied and updates the status of messages waiting.
func (this *Ackqueue) Ack(msg message.Message) error {
this.mu.Lock()
defer this.mu.Unlock()
switch msg.Type() {
case message.PUBACK, message.PUBREC, message.PUBREL, message.PUBCOMP, message.SUBACK, message.UNSUBACK:
// Check to see if the message w/ the same packet ID is in the queue
i, ok := this.emap[msg.PacketId()]
if ok {
// If message w/ the packet ID exists, update the message state and copy
// the ack message
this.ring[i].State = msg.Type()
ml := msg.Len()
this.ring[i].Ackbuf = make([]byte, ml)
_, err := msg.Encode(this.ring[i].Ackbuf)
if err != nil {
return err
}
//glog.Debugf("Acked: %v", msg)
//} else {
//glog.Debugf("Cannot ack %s message with packet ID %d", msg.Type(), msg.PacketId())
}
case message.PINGRESP:
if this.ping.Mtype == message.PINGREQ {
this.ping.State = message.PINGRESP
}
default:
return errAckMessage
}
return nil
}
// Acked() returns the list of messages that have completed the ack cycle.
func (this *Ackqueue) Acked() []ackmsg {
this.mu.Lock()
defer this.mu.Unlock()
this.ackdone = this.ackdone[0:0]
if this.ping.State == message.PINGRESP {
this.ackdone = append(this.ackdone, this.ping)
this.ping = ackmsg{}
}
FORNOTEMPTY:
for !this.empty() {
switch this.ring[this.head].State {
case message.PUBACK, message.PUBREL, message.PUBCOMP, message.SUBACK, message.UNSUBACK:
this.ackdone = append(this.ackdone, this.ring[this.head])
this.removeHead()
default:
break FORNOTEMPTY
}
}
return this.ackdone
}
func (this *Ackqueue) insert(pktid uint16, msg message.Message, onComplete interface{}) error {
if this.full() {
this.grow()
}
if _, ok := this.emap[pktid]; !ok {
// message length
ml := msg.Len()
// ackmsg
am := ackmsg{
Mtype: msg.Type(),
State: message.RESERVED,
Pktid: msg.PacketId(),
Msgbuf: make([]byte, ml),
OnComplete: onComplete,
}
if _, err := msg.Encode(am.Msgbuf); err != nil {
return err
}
this.ring[this.tail] = am
this.emap[pktid] = this.tail
this.tail = this.increment(this.tail)
this.count++
} else {
// If packet w/ pktid already exist, then this must be a PUBLISH message
// Other message types should never send with the same packet ID
pm, ok := msg.(*message.PublishMessage)
if !ok {
return fmt.Errorf("ack/insert: duplicate packet ID for %s message", msg.Name())
}
// If this is a publish message, then the DUP flag must be set. This is the
// only scenario in which we will receive duplicate messages.
if pm.Dup() {
return fmt.Errorf("ack/insert: duplicate packet ID for PUBLISH message, but DUP flag is not set")
}
// Since it's a dup, there's really nothing we need to do. Moving on...
}
return nil
}
func (this *Ackqueue) removeHead() error {
if this.empty() {
return errQueueEmpty
}
it := this.ring[this.head]
// set this to empty ackmsg{} to ensure GC will collect the buffer
this.ring[this.head] = ackmsg{}
this.head = this.increment(this.head)
this.count--
delete(this.emap, it.Pktid)
return nil
}
func (this *Ackqueue) grow() {
if math.MaxInt64/2 < this.size {
panic("new size will overflow int64")
}
newsize := this.size << 1
newmask := newsize - 1
newring := make([]ackmsg, newsize)
if this.tail > this.head {
copy(newring, this.ring[this.head:this.tail])
} else {
copy(newring, this.ring[this.head:])
copy(newring[this.size-this.head:], this.ring[:this.tail])
}
this.size = newsize
this.mask = newmask
this.ring = newring
this.head = 0
this.tail = this.count
this.emap = make(map[uint16]int64, this.size)
for i := int64(0); i < this.tail; i++ {
this.emap[this.ring[i].Pktid] = i
}
}
func (this *Ackqueue) len() int {
return int(this.count)
}
func (this *Ackqueue) cap() int {
return int(this.size)
}
func (this *Ackqueue) index(n int64) int64 {
return n & this.mask
}
func (this *Ackqueue) full() bool {
return this.count == this.size
}
func (this *Ackqueue) empty() bool {
return this.count == 0
}
func (this *Ackqueue) increment(n int64) int64 {
return this.index(n + 1)
}
func powerOfTwo64(n int64) bool {
return n != 0 && (n&(n-1)) == 0
}
func roundUpPowerOfTwo64(n int64) int64 {
n--
n |= n >> 1
n |= n >> 2
n |= n >> 4
n |= n >> 8
n |= n >> 16
n |= n >> 32
n++
return n
}