@ -208,23 +208,37 @@ type ClientSubscription struct {
channel reflect . Value
namespace string
subid string
in chan json . RawMessage
quitOnce sync . Once // ensures quit is closed once
quit chan struct { } // quit is closed when the subscription exits
errOnce sync . Once // ensures err is closed once
err chan error
// The in channel receives notification values from client dispatcher.
in chan json . RawMessage
// The error channel receives the error from the forwarding loop.
// It is closed by Unsubscribe.
err chan error
errOnce sync . Once
// Closing of the subscription is requested by sending on 'quit'. This is handled by
// the forwarding loop, which closes 'forwardDone' when it has stopped sending to
// sub.channel. Finally, 'unsubDone' is closed after unsubscribing on the server side.
quit chan error
forwardDone chan struct { }
unsubDone chan struct { }
}
// This is the sentinel value sent on sub.quit when Unsubscribe is called.
var errUnsubscribed = errors . New ( "unsubscribed" )
func newClientSubscription ( c * Client , namespace string , channel reflect . Value ) * ClientSubscription {
sub := & ClientSubscription {
client : c ,
namespace : namespace ,
etype : channel . Type ( ) . Elem ( ) ,
channel : channel ,
quit : make ( chan struct { } ) ,
err : make ( chan error , 1 ) ,
in : make ( chan json . RawMessage ) ,
client : c ,
namespace : namespace ,
etype : channel . Type ( ) . Elem ( ) ,
channel : channel ,
in : make ( chan json . RawMessage ) ,
quit : make ( chan error ) ,
forwardDone : make ( chan struct { } ) ,
unsubDone : make ( chan struct { } ) ,
err : make ( chan error , 1 ) ,
}
return sub
}
@ -232,9 +246,9 @@ func newClientSubscription(c *Client, namespace string, channel reflect.Value) *
// Err returns the subscription error channel. The intended use of Err is to schedule
// resubscription when the client connection is closed unexpectedly.
//
// The error channel receives a value when the subscription has ended due
// to an error. The received error is nil if Close has been called
// on the underlying client and no other error has occurred.
// The error channel receives a value when the subscription has ended due to an error. The
// received error is nil if Close has been called on the underlying client and no other
// error has occurred.
//
// The error channel is closed when Unsubscribe is called on the subscription.
func ( sub * ClientSubscription ) Err ( ) <- chan error {
@ -244,41 +258,63 @@ func (sub *ClientSubscription) Err() <-chan error {
// Unsubscribe unsubscribes the notification and closes the error channel.
// It can safely be called more than once.
func ( sub * ClientSubscription ) Unsubscribe ( ) {
sub . quitWithError ( true , nil )
sub . errOnce . Do ( func ( ) { close ( sub . err ) } )
}
func ( sub * ClientSubscription ) quitWithError ( unsubscribeServer bool , err error ) {
sub . quitOnce . Do ( func ( ) {
// The dispatch loop won't be able to execute the unsubscribe call
// if it is blocked on deliver. Close sub.quit first because it
// unblocks deliver.
close ( sub . quit )
if unsubscribeServer {
sub . requestUnsubscribe ( )
}
if err != nil {
if err == ErrClientQuit {
err = nil // Adhere to subscription semantics.
}
sub . err <- err
sub . errOnce . Do ( func ( ) {
select {
case sub . quit <- errUnsubscribed :
<- sub . unsubDone
case <- sub . unsubDone :
}
close ( sub . err )
} )
}
// deliver is called by the client's message dispatcher to send a notification value.
func ( sub * ClientSubscription ) deliver ( result json . RawMessage ) ( ok bool ) {
select {
case sub . in <- result :
return true
case <- sub . quit :
case <- sub . forwardDone :
return false
}
}
func ( sub * ClientSubscription ) start ( ) {
sub . quitWithError ( sub . forward ( ) )
// close is called by the client's message dispatcher when the connection is closed.
func ( sub * ClientSubscription ) close ( err error ) {
select {
case sub . quit <- err :
case <- sub . forwardDone :
}
}
// run is the forwarding loop of the subscription. It runs in its own goroutine and
// is launched by the client's handler after the subscription has been created.
func ( sub * ClientSubscription ) run ( ) {
defer close ( sub . unsubDone )
unsubscribe , err := sub . forward ( )
// The client's dispatch loop won't be able to execute the unsubscribe call if it is
// blocked in sub.deliver() or sub.close(). Closing forwardDone unblocks them.
close ( sub . forwardDone )
// Call the unsubscribe method on the server.
if unsubscribe {
sub . requestUnsubscribe ( )
}
// Send the error.
if err != nil {
if err == ErrClientQuit {
// ErrClientQuit gets here when Client.Close is called. This is reported as a
// nil error because it's not an error, but we can't close sub.err here.
err = nil
}
sub . err <- err
}
}
// forward is the forwarding loop. It takes in RPC notifications and sends them
// on the subscription channel.
func ( sub * ClientSubscription ) forward ( ) ( unsubscribeServer bool , err error ) {
cases := [ ] reflect . SelectCase {
{ Dir : reflect . SelectRecv , Chan : reflect . ValueOf ( sub . quit ) } ,
@ -286,7 +322,7 @@ func (sub *ClientSubscription) forward() (unsubscribeServer bool, err error) {
{ Dir : reflect . SelectSend , Chan : sub . channel } ,
}
buffer := list . New ( )
defer buffer . Init ( )
for {
var chosen int
var recv reflect . Value
@ -301,7 +337,15 @@ func (sub *ClientSubscription) forward() (unsubscribeServer bool, err error) {
switch chosen {
case 0 : // <-sub.quit
return false , nil
if ! recv . IsNil ( ) {
err = recv . Interface ( ) . ( error )
}
if err == errUnsubscribed {
// Exiting because Unsubscribe was called, unsubscribe on server.
return true , nil
}
return false , err
case 1 : // <-sub.in
val , err := sub . unmarshal ( recv . Interface ( ) . ( json . RawMessage ) )
if err != nil {
@ -311,6 +355,7 @@ func (sub *ClientSubscription) forward() (unsubscribeServer bool, err error) {
return true , ErrSubscriptionQueueOverflow
}
buffer . PushBack ( val )
case 2 : // sub.channel<-
cases [ 2 ] . Send = reflect . Value { } // Don't hold onto the value.
buffer . Remove ( buffer . Front ( ) )
Felix Lange
4 years ago
committed by
GitHub