routing/validation_barrier: adds ErrVBarrierShuttingDown

Adds a new error ErrVBarrierShuttingDown that is returned
from WaitForDependants if the validation barrier's quit
chan is closed. This allows any blocked goroutines to
distinguish whether the dependent task has been completed,
or if validation should be aborted entirely.

routing/validation_barrier.go

@@ -1,12 +1,18 @@
 package routing
 
 import (
+	"errors"
 	"sync"
 
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnwire"
 )
 
+// ErrVBarrierShuttingDown signals that the barrier has been requested to
+// shutdown, and that the caller should not treat the wait condition as
+// fulfilled.
+var ErrVBarrierShuttingDown = errors.New("validation barrier shutting down")
+
 // ValidationBarrier is a barrier used to ensure proper validation order while
 // concurrently validating new announcements for channel edges, and the
 // attributes of channel edges.  It uses this set of maps (protected by this
@@ -152,7 +158,7 @@ func (v *ValidationBarrier) CompleteJob() {
 // finished executing. This allows us a graceful way to schedule goroutines
 // based on any pending uncompleted dependent jobs. If this job doesn't have an
 // active dependent, then this function will return immediately.
-func (v *ValidationBarrier) WaitForDependants(job interface{}) {
+func (v *ValidationBarrier) WaitForDependants(job interface{}) error {
 
 	var (
 		signal chan struct{}
@@ -181,13 +187,13 @@ func (v *ValidationBarrier) WaitForDependants(job interface{}) {
 	case *lnwire.AnnounceSignatures:
 		// TODO(roasbeef): need to wait on chan ann?
 		v.Unlock()
-		return
+		return nil
 	case *channeldb.ChannelEdgeInfo:
 		v.Unlock()
-		return
+		return nil
 	case *lnwire.ChannelAnnouncement:
 		v.Unlock()
-		return
+		return nil
 	}
 	v.Unlock()
 
@@ -196,10 +202,13 @@ func (v *ValidationBarrier) WaitForDependants(job interface{}) {
 	if ok {
 		select {
 		case <-v.quit:
-			return
+			return ErrVBarrierShuttingDown
 		case <-signal:
+			return nil
 		}
 	}
+
+	return nil
 }
 
 // SignalDependants will signal any jobs that are dependent on this job that