add option to control number of synchronous validation workers

pubsub.go

@@ -99,6 +99,9 @@ type PubSub struct {
 	// validateThrottle limits the number of active validation goroutines
 	validateThrottle chan struct{}
 
+	// this is the number of synchronous validation workers
+	validateWorkers int
+
 	// eval thunk in event loop
 	eval chan func()
 
@@ -194,6 +197,7 @@ func NewPubSub(ctx context.Context, h host.Host, rt PubSubRouter, opts ...Option
 		blacklistPeer:    make(chan peer.ID),
 		seenMessages:     timecache.NewTimeCache(TimeCacheDuration),
 		counter:          uint64(time.Now().UnixNano()),
+		validateWorkers:  runtime.NumCPU(),
 	}
 
 	for _, opt := range opts {
@@ -216,8 +220,7 @@ func NewPubSub(ctx context.Context, h host.Host, rt PubSubRouter, opts ...Option
 
 	go ps.processLoop(ctx)
 
-	numcpu := runtime.NumCPU()
-	for i := 0; i < numcpu; i++ {
+	for i := 0; i < ps.validateWorkers; i++ {
 		go ps.validateWorker()
 	}
 
@@ -233,6 +236,18 @@ func WithValidateThrottle(n int) Option {
 	}
 }
 
+// WithValidateWorkers sets the number of synchronous validation worker goroutines.
+// Defaults to NumCPU.
+func WithValidateWorkers(n int) Option {
+	return func(ps *PubSub) error {
+		if n > 0 {
+			ps.validateWorkers = n
+			return nil
+		}
+		return fmt.Errorf("number of validation workers must be > 0")
+	}
+}
+
 // WithMessageSigning enables or disables message signing (enabled by default).
 func WithMessageSigning(enabled bool) Option {
 	return func(p *PubSub) error {