p2p/discover: remove hot-spin in table refresh trigger

Author: fjl

p2p/discover/lookup.go

@@ -153,6 +153,7 @@ type lookupIterator struct {
 	cancel        func()
 	lookup        *lookup
 	tabRefreshing <-chan struct{}
+	lastWait      time.Time
 }
 
 type lookupFunc func(ctx context.Context) *lookup
@@ -220,6 +221,21 @@ func (it *lookupIterator) lookupFailed(tab *Table, timeout time.Duration) {
 		return
 	}
 
+	// Ensure we trigger refresh at most every 2s.
+	const minInterval = 2 * time.Second
+	now := time.Now()
+	diff := now.Sub(it.lastWait)
+	it.lastWait = now
+	if diff < minInterval {
+		wait := time.NewTimer(diff)
+		defer wait.Stop()
+		select {
+		case <-wait.C:
+		case <-tout.Done():
+			return
+		}
+	}
+
 	// Wait for ongoing refresh operation, or trigger one.
 	if it.tabRefreshing == nil {
 		it.tabRefreshing = tab.refresh()