Add allocator.PeerGone

The function is registered within the mesh gc and it is responsible
for removing gone nicknames (#2057).

ipam/allocator.go

@@ -90,11 +90,13 @@ type Config struct {
 // NewAllocator creates and initialises a new Allocator
 func NewAllocator(config Config) *Allocator {
 	var participant paxos.Participant
+
 	if config.IsObserver {
 		participant = paxos.NewObserver()
 	} else {
 		participant = paxos.NewNode(config.OurName, config.OurUID, 0)
 	}
+
 	return &Allocator{
 		ourName:     config.OurName,
 		seed:        config.Seed,
@@ -485,6 +487,22 @@ func (alloc *Allocator) annotatePeernames(names []mesh.PeerName) []string {
 	return res
 }
 
+// PeerGone removes nicknames of peers which are no longer mentioned
+// in the ring. Async.
+//
+// NB: the function is invoked by the gossip library routines and should be
+//     registered manually.
+func (alloc *Allocator) PeerGone(peerName mesh.PeerName) {
+	alloc.debugln("PeerGone: peer %s", peerName)
+
+	alloc.actionChan <- func() {
+		ringPeers := alloc.ring.PeerNames()
+		if _, ok := ringPeers[peerName]; !ok {
+			delete(alloc.nicknames, peerName)
+		}
+	}
+}
+
 func decodeRange(msg []byte) (r address.Range, err error) {
 	decoder := gob.NewDecoder(bytes.NewReader(msg))
 	return r, decoder.Decode(&r)

prog/weaver/main.go

@@ -452,6 +452,7 @@ func createAllocator(router *weave.NetworkRouter, config ipamConfig, db db.DB, i
 
 	allocator.SetInterfaces(router.NewGossip("IPallocation", allocator))
 	allocator.Start()
+	router.Peers.OnGC(func(peer *mesh.Peer) { allocator.PeerGone(peer.Name) })
 
 	return allocator, defaultSubnet
 }