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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package netchan
import (
"gob"
"io"
"os"
"reflect"
"sync"
"time"
)
// The direction of a connection from the client's perspective.
type Dir int
const (
Recv Dir = iota
Send
)
func (dir Dir) String() string {
switch dir {
case Recv:
return "Recv"
case Send:
return "Send"
}
return "???"
}
// Payload types
const (
payRequest = iota // request structure follows
payError // error structure follows
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 {
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, with space for size buffered values. If count is -1, it means unlimited.
type request struct {
Name string
Count int64
Size int
Dir Dir
}
// Sent with a header to report an error.
type error struct {
Error string
}
// Used to unify management of acknowledgements for import and export.
type unackedCounter interface {
unackedCount() int64
ack() int64
seq() int64
}
// A channel and its direction.
type chanDir struct {
ch reflect.Value
dir Dir
}
// clientSet contains the objects and methods needed for tracking
// clients of an exporter and draining outstanding messages.
type clientSet struct {
mu sync.Mutex // protects access to channel and client maps
names map[string]*chanDir
clients map[unackedCounter]bool
}
// Mutex-protected encoder and decoder pair.
type encDec struct {
decLock sync.Mutex
dec *gob.Decoder
encLock sync.Mutex
enc *gob.Encoder
}
func newEncDec(conn io.ReadWriter) *encDec {
return &encDec{
dec: gob.NewDecoder(conn),
enc: gob.NewEncoder(conn),
}
}
// Decode an item from the connection.
func (ed *encDec) decode(value reflect.Value) os.Error {
ed.decLock.Lock()
err := ed.dec.DecodeValue(value)
if err != nil {
// TODO: tear down connection?
}
ed.decLock.Unlock()
return err
}
// Encode a header and payload onto the connection.
func (ed *encDec) encode(hdr *header, payloadType int, payload interface{}) os.Error {
ed.encLock.Lock()
hdr.PayloadType = payloadType
err := ed.enc.Encode(hdr)
if err == nil {
if payload != nil {
err = ed.enc.Encode(payload)
}
}
if err != nil {
// TODO: tear down connection if there is an error?
}
ed.encLock.Unlock()
return err
}
// See the comment for Exporter.Drain.
func (cs *clientSet) drain(timeout int64) os.Error {
startTime := time.Nanoseconds()
for {
pending := false
cs.mu.Lock()
// Any messages waiting for a client?
for _, chDir := range cs.names {
if chDir.ch.Len() > 0 {
pending = true
}
}
// Any unacknowledged messages?
for client := range cs.clients {
n := client.unackedCount()
if n > 0 { // Check for > rather than != just to be safe.
pending = true
break
}
}
cs.mu.Unlock()
if !pending {
break
}
if timeout > 0 && time.Nanoseconds()-startTime >= timeout {
return os.NewError("timeout")
}
time.Sleep(100 * 1e6) // 100 milliseconds
}
return nil
}
// See the comment for Exporter.Sync.
func (cs *clientSet) sync(timeout int64) os.Error {
startTime := time.Nanoseconds()
// seq remembers the clients and their seqNum at point of entry.
seq := make(map[unackedCounter]int64)
for client := range cs.clients {
seq[client] = client.seq()
}
for {
pending := false
cs.mu.Lock()
// Any unacknowledged messages? Look only at clients that existed
// when we started and are still in this client set.
for client := range seq {
if _, ok := cs.clients[client]; ok {
if client.ack() < seq[client] {
pending = true
break
}
}
}
cs.mu.Unlock()
if !pending {
break
}
if timeout > 0 && time.Nanoseconds()-startTime >= timeout {
return os.NewError("timeout")
}
time.Sleep(100 * 1e6) // 100 milliseconds
}
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.
closed bool
// 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.closed {
return
}
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)
}
nch.closed = true
}
// 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, ok 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()
}
// 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")
}
}