htlcswitch: add new mailBox abstraction to the package

In this commit, we add a new abstraction to the package: the mailBox. The mailBox is a non-blocking, concurrent safe, in-order queue for delivering messages to a given channelLink instance. With this abstraction in place, we can now allow the switch to no longer launch a new goroutine for each forwarded HTLC, or instantiated user payment.
2017-11-10 19:51:01 -08:00
1 parent 1734f96544
commit 890559edfa
@@ -0,0 +1,248 @@
+package htlcswitch
+
+import (
+	"sync"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+// mailBox is an interface which represents a concurrent-safe, in-order
+// delivery queue for messages from the network and also from the main switch.
+// This struct servers as a buffer between incoming messages, and messages to
+// the handled by the link. Each of the mutating methods within this interface
+// should be implemented in a non-blocking manner.
+type mailBox interface {
+	// AddMessage appends a new message to the end of the message queue.
+	AddMessage(msg lnwire.Message) error
+
+	// AddPacket appends a new message to the end of the packet queue.
+	AddPacket(pkt *htlcPacket) error
+
+	// MessageOutBox returns a channel that any new messages ready for
+	// delivery will be sent on.
+	MessageOutBox() chan lnwire.Message
+
+	// PacketOutBox returns a channel that any new packets ready for
+	// delivery will be sent on.
+	PacketOutBox() chan *htlcPacket
+
+	// Start starts the mailbox and any goroutines it needs to operate
+	// properly.
+	Start() error
+
+	// Stop signals the mailbox and its goroutines for a graceful shutdown.
+	Stop() error
+}
+
+// memoryMailBox is an implementation of the mailBox struct backed by purely
+// in-memory queues.
+type memoryMailBox struct {
+	wireMessages []lnwire.Message
+	wireMtx      sync.Mutex
+	wireCond     *sync.Cond
+
+	messageOutbox chan lnwire.Message
+
+	htlcPkts []*htlcPacket
+	pktMtx   sync.Mutex
+	pktCond  *sync.Cond
+
+	pktOutbox chan *htlcPacket
+
+	wg   sync.WaitGroup
+	quit chan struct{}
+}
+
+// newMemoryMailBox creates a new instance of the memoryMailBox.
+func newMemoryMailBox() *memoryMailBox {
+	box := &memoryMailBox{
+		quit:          make(chan struct{}),
+		messageOutbox: make(chan lnwire.Message),
+		pktOutbox:     make(chan *htlcPacket),
+	}
+	box.wireCond = sync.NewCond(&box.wireMtx)
+	box.pktCond = sync.NewCond(&box.pktMtx)
+
+	return box
+}
+
+// A compile time assertion to ensure that memoryMailBox meets the mailBox
+// interface.
+var _ mailBox = (*memoryMailBox)(nil)
+
+// courierType is an enum that reflects the distinct types of messages a
+// mailBox can handle. Each type will be placed in an isolated mail box and
+// will have a dedicated goroutine for delivering the messages.
+type courierType uint8
+
+const (
+	// wireCourier is a type of courier that handles wire messages.
+	wireCourier courierType = iota
+
+	// pktCourier is a type of courier that handles hltc packets.
+	pktCourier
+)
+
+// Start starts the mailbox and any goroutines it needs to operate properly.
+//
+// NOTE: This method is part of the mailBox interface.
+func (m *memoryMailBox) Start() error {
+	m.wg.Add(2)
+	go m.mailCourier(wireCourier)
+	go m.mailCourier(pktCourier)
+
+	return nil
+}
+
+// Stop signals the mailbox and its goroutines for a graceful shutdown.
+//
+// NOTE: This method is part of the mailBox interface.
+func (m *memoryMailBox) Stop() error {
+	close(m.quit)
+
+	m.wireCond.Signal()
+	m.pktCond.Signal()
+
+	return nil
+}
+
+// mailCourier is a dedicated goroutine whose job is to reliably deliver
+// messages of a particular type. There are two types of couriers: wire
+// couriers, and mail couriers. Depending on the passed courierType, this
+// goroutine will assume one of two roles.
+func (m *memoryMailBox) mailCourier(cType courierType) {
+	defer m.wg.Done()
+
+	// TODO(roasbeef): refactor...
+
+	for {
+		// First, we'll check our condition. If our target mailbox is
+		// empty, then we'll wait until a new item is added.
+		switch cType {
+		case wireCourier:
+			m.wireCond.L.Lock()
+			for len(m.wireMessages) == 0 {
+				m.wireCond.Wait()
+
+				select {
+				case <-m.quit:
+					m.wireCond.L.Unlock()
+					return
+				default:
+				}
+			}
+
+		case pktCourier:
+			m.pktCond.L.Lock()
+			for len(m.htlcPkts) == 0 {
+				m.pktCond.Wait()
+
+				select {
+				case <-m.quit:
+					m.pktCond.L.Unlock()
+					return
+				default:
+				}
+			}
+		}
+
+		// Grab the datum off the front of the queue, shifting the
+		// slice's reference down one in order to remove the datum from
+		// the queue.
+		var (
+			nextPkt *htlcPacket
+			nextMsg lnwire.Message
+		)
+		switch cType {
+		case wireCourier:
+			nextMsg = m.wireMessages[0]
+			m.wireMessages[0] = nil // Set to nil to prevent GC leak.
+			m.wireMessages = m.wireMessages[1:]
+		case pktCourier:
+			nextPkt = m.htlcPkts[0]
+			m.htlcPkts[0] = nil // Set to nil to prevent GC leak.
+			m.htlcPkts = m.htlcPkts[1:]
+		}
+
+		// Now that we're done with the condition, we can unlock it to
+		// allow any callers to append to the end of our target queue.
+		switch cType {
+		case wireCourier:
+			m.wireCond.L.Unlock()
+		case pktCourier:
+			m.pktCond.L.Unlock()
+		}
+
+		// With the next message obtained, we'll now select to attempt
+		// to deliver the message. If we receive a kill signal, then
+		// we'll bail out.
+		switch cType {
+		case wireCourier:
+			select {
+			case m.messageOutbox <- nextMsg:
+			case <-m.quit:
+				return
+			}
+
+		case pktCourier:
+			select {
+			case m.pktOutbox <- nextPkt:
+			case <-m.quit:
+				return
+			}
+		}
+
+	}
+}
+
+// AddMessage appends a new message to the end of the message queue.
+//
+// NOTE: This method is safe for concrete use and part of the mailBox
+// interface.
+func (m *memoryMailBox) AddMessage(msg lnwire.Message) error {
+	// First, we'll lock the condition, and add the message to the end of
+	// the wire message inbox.
+	m.wireCond.L.Lock()
+	m.wireMessages = append(m.wireMessages, msg)
+	m.wireCond.L.Unlock()
+
+	// With the message added, we signal to the mailCourier that there are
+	// additional messages to deliver.
+	m.wireCond.Signal()
+
+	return nil
+}
+
+// AddPacket appends a new message to the end of the packet queue.
+//
+// NOTE: This method is safe for concrete use and part of the mailBox
+// interface.
+func (m *memoryMailBox) AddPacket(pkt *htlcPacket) error {
+	// First, we'll lock the condition, and add the packet to the end of
+	// the htlc packet inbox.
+	m.pktCond.L.Lock()
+	m.htlcPkts = append(m.htlcPkts, pkt)
+	m.pktCond.L.Unlock()
+
+	// With the packet added, we signal to the mailCourier that there are
+	// additional packets to consume.
+	m.pktCond.Signal()
+
+	return nil
+}
+
+// MessageOutBox returns a channel that any new messages ready for delivery
+// will be sent on.
+//
+// NOTE: This method is part of the mailBox interface.
+func (m *memoryMailBox) MessageOutBox() chan lnwire.Message {
+	return m.messageOutbox
+}
+
+// PacketOutBox returns a channel that any new packets ready for delivery will
+// be sent on.
+//
+// NOTE: This method is part of the mailBox interface.
+func (m *memoryMailBox) PacketOutBox() chan *htlcPacket {
+	return m.pktOutbox
+}