Merge pull request #43 from libp2p/fix/query-event-overhead

fix: avoid subscribing to query events unless necessary

Author: Stebalien

go.mod

@@ -4,7 +4,7 @@ require (
 	github.com/hashicorp/errwrap v1.0.0
 	github.com/hashicorp/go-multierror v1.1.0
 	github.com/ipfs/go-cid v0.0.5
-	github.com/libp2p/go-libp2p-core v0.5.1
+	github.com/libp2p/go-libp2p-core v0.5.3
 	github.com/libp2p/go-libp2p-record v0.1.2
 	github.com/multiformats/go-multihash v0.0.13
 )

go.sum

@@ -77,6 +77,8 @@ github.com/libp2p/go-libp2p-core v0.2.5 h1:iP1PIiIrlRrGbE1fYq2918yBc5NlCH3pFuIPS
 github.com/libp2p/go-libp2p-core v0.2.5/go.mod h1:6+5zJmKhsf7yHn1RbmYDu08qDUpIUxGdqHuEZckmZOA=
 github.com/libp2p/go-libp2p-core v0.5.1 h1:6Cu7WljPQtGY2krBlMoD8L/zH3tMUsCbqNFH7cZwCoI=
 github.com/libp2p/go-libp2p-core v0.5.1/go.mod h1:uN7L2D4EvPCvzSH5SrhR72UWbnSGpt5/a35Sm4upn4Y=
+github.com/libp2p/go-libp2p-core v0.5.3 h1:b9W3w7AZR2n/YJhG8d0qPFGhGhCWKIvPuJgp4hhc4MM=
+github.com/libp2p/go-libp2p-core v0.5.3/go.mod h1:uN7L2D4EvPCvzSH5SrhR72UWbnSGpt5/a35Sm4upn4Y=
 github.com/libp2p/go-libp2p-record v0.1.2 h1:M50VKzWnmUrk/M5/Dz99qO9Xh4vs8ijsK+7HkJvRP+0=
 github.com/libp2p/go-libp2p-record v0.1.2/go.mod h1:pal0eNcT5nqZaTV7UGhqeGqxFgGdsU/9W//C8dqjQDk=
 github.com/libp2p/go-msgio v0.0.4/go.mod h1:63lBBgOTDKQL6EWazRMCwXsEeEeK9O2Cd+0+6OOuipQ=

parallel.go

@@ -293,6 +293,10 @@ func (r Parallel) forKey(key string) Parallel {
 // routers fail.
 func (r Parallel) mergeQueryEvents(ctx context.Context) (context.Context, context.CancelFunc) {
 	subCtx, cancel := context.WithCancel(ctx)
+	if !routing.SubscribesToQueryEvents(ctx) {
+		return subCtx, cancel
+	}
+
 	subCtx, evCh := routing.RegisterForQueryEvents(subCtx)
 	go func() {
 		var errEvt *routing.QueryEvent