1 files changed, 144 insertions, 4 deletions
diff --git a/src/pkg/netchan/common.go b/src/pkg/netchan/common.go
index bde3087a5..6c085484e 100644
--- a/src/pkg/netchan/common.go
+++ b/src/pkg/netchan/common.go
@@ -38,21 +38,24 @@ const (
 	payData           // user payload follows
 	payAck            // acknowledgement; no payload
 	payClosed         // channel is now closed
+	payAckSend        // payload has been delivered.
 )
 
 // A header is sent as a prefix to every transmission.  It will be followed by
 // a request structure, an error structure, or an arbitrary user payload structure.
 type header struct {
-	Name        string
+	Id          int
 	PayloadType int
 	SeqNum      int64
 }
 
 // Sent with a header once per channel from importer to exporter to report
 // that it wants to bind to a channel with the specified direction for count
-// messages.  If count is -1, it means unlimited.
+// messages, with space for size buffered values. If count is -1, it means unlimited.
 type request struct {
+	Name  string
 	Count int64
+	Size  int
 	Dir   Dir
 }
 
@@ -78,7 +81,7 @@ type chanDir struct {
 // clients of an exporter and draining outstanding messages.
 type clientSet struct {
 	mu      sync.Mutex // protects access to channel and client maps
-	chans   map[string]*chanDir
+	names   map[string]*chanDir
 	clients map[unackedCounter]bool
 }
 
@@ -132,7 +135,7 @@ func (cs *clientSet) drain(timeout int64) os.Error {
 		pending := false
 		cs.mu.Lock()
 		// Any messages waiting for a client?
-		for _, chDir := range cs.chans {
+		for _, chDir := range cs.names {
 			if chDir.ch.Len() > 0 {
 				pending = true
 			}
@@ -189,3 +192,140 @@ func (cs *clientSet) sync(timeout int64) os.Error {
 	}
 	return nil
 }
+
+// A netChan represents a channel imported or exported
+// on a single connection. Flow is controlled by the receiving
+// side by sending payAckSend messages when values
+// are delivered into the local channel.
+type netChan struct {
+	*chanDir
+	name string
+	id   int
+	size int // buffer size of channel.
+
+	// sender-specific state
+	ackCh chan bool // buffered with space for all the acks we need
+	space int       // available space.
+
+	// receiver-specific state
+	sendCh chan reflect.Value // buffered channel of values received from other end.
+	ed     *encDec            // so that we can send acks.
+	count  int64              // number of values still to receive.
+}
+
+// Create a new netChan with the given name (only used for
+// messages), id, direction, buffer size, and count.
+// The connection to the other side is represented by ed.
+func newNetChan(name string, id int, ch *chanDir, ed *encDec, size int, count int64) *netChan {
+	c := &netChan{chanDir: ch, name: name, id: id, size: size, ed: ed, count: count}
+	if c.dir == Send {
+		c.ackCh = make(chan bool, size)
+		c.space = size
+	}
+	return c
+}
+
+// Close the channel.
+func (nch *netChan) close() {
+	if nch.dir == Recv {
+		if nch.sendCh != nil {
+			// If the sender goroutine is active, close the channel to it.
+			// It will close nch.ch when it can.
+			close(nch.sendCh)
+		} else {
+			nch.ch.Close()
+		}
+	} else {
+		nch.ch.Close()
+		close(nch.ackCh)
+	}
+}
+
+// Send message from remote side to local receiver.
+func (nch *netChan) send(val reflect.Value) {
+	if nch.dir != Recv {
+		panic("send on wrong direction of channel")
+	}
+	if nch.sendCh == nil {
+		// If possible, do local send directly and ack immediately.
+		if nch.ch.TrySend(val) {
+			nch.sendAck()
+			return
+		}
+		// Start sender goroutine to manage delayed delivery of values.
+		nch.sendCh = make(chan reflect.Value, nch.size)
+		go nch.sender()
+	}
+	select {
+	case nch.sendCh <- val:
+		// ok
+	default:
+		// TODO: should this be more resilient?
+		panic("netchan: remote sender sent more values than allowed")
+	}
+}
+
+// sendAck sends an acknowledgment that a message has left
+// the channel's buffer. If the messages remaining to be sent
+// will fit in the channel's buffer, then we don't
+// need to send an ack.
+func (nch *netChan) sendAck() {
+	if nch.count < 0 || nch.count > int64(nch.size) {
+		nch.ed.encode(&header{Id: nch.id}, payAckSend, nil)
+	}
+	if nch.count > 0 {
+		nch.count--
+	}
+}
+
+// The sender process forwards items from the sending queue
+// to the destination channel, acknowledging each item.
+func (nch *netChan) sender() {
+	if nch.dir != Recv {
+		panic("sender on wrong direction of channel")
+	}
+	// When Exporter.Hangup is called, the underlying channel is closed,
+	// and so we may get a "too many operations on closed channel" error
+	// if there are outstanding messages in sendCh.
+	// Make sure that this doesn't panic the whole program.
+	defer func() {
+		if r := recover(); r != nil {
+			// TODO check that r is "too many operations", otherwise re-panic.
+		}
+	}()
+	for v := range nch.sendCh {
+		nch.ch.Send(v)
+		nch.sendAck()
+	}
+	nch.ch.Close()
+}
+
+// Receive value from local side for sending to remote side.
+func (nch *netChan) recv() (val reflect.Value, closed bool) {
+	if nch.dir != Send {
+		panic("recv on wrong direction of channel")
+	}
+
+	if nch.space == 0 {
+		// Wait for buffer space.
+		<-nch.ackCh
+		nch.space++
+	}
+	nch.space--
+	return nch.ch.Recv(), nch.ch.Closed()
+}
+
+// acked is called when the remote side indicates that
+// a value has been delivered.
+func (nch *netChan) acked() {
+	if nch.dir != Send {
+		panic("recv on wrong direction of channel")
+	}
+	select {
+	case nch.ackCh <- true:
+		// ok
+	default:
+		// TODO: should this be more resilient?
+		panic("netchan: remote receiver sent too many acks")
+	}
+}