internal/gcpdial: throttle polling for instances

gcpdial polls for instances in case instances from the sandbox instance
group change. Unfortunately, it is causing us to go over quota in our
production project, which breaks other services (mainly deploying from
Cloud Build).

This change introduces a 10s ticker. Verified locally using
internal/gcpdial/gcpdialtool.

Updates golang/go#38315

Change-Id: I36009397233c6fc1663a7f2cee4f47caea1ca161
Reviewed-on: https://go-review.googlesource.com/c/playground/+/227648
Run-TryBot: Alexander Rakoczy <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: toothrot

internal/gcpdial/gcpdial.go

@@ -18,7 +18,7 @@ import (
 	"sync"
 	"time"
 
-	compute "google.golang.org/api/compute/v1"
+	"google.golang.org/api/compute/v1"
 )
 
 type Dialer struct {
@@ -188,46 +188,58 @@ func (d *Dialer) pickIP() (string, bool) {
 }
 
 func (d *Dialer) poll() {
+	// TODO(golang.org/issue/38315) - Plumb a context in here correctly
+	ctx := context.TODO()
+	t := time.NewTicker(10 * time.Second)
+	defer t.Stop()
 	for {
-		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
-		res, err := d.lister.ListInstances(ctx)
-		cancel()
-		if err != nil {
-			log.Printf("gcpdial: polling %v: %v", d.lister, err)
-			time.Sleep(10 * time.Second)
-			continue
+		d.pollOnce(ctx)
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
 		}
+	}
+}
 
-		want := map[string]bool{} // the res []string turned into a set
-		for _, instURL := range res {
-			want[instURL] = true
-		}
+func (d *Dialer) pollOnce(ctx context.Context) {
+	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
+	res, err := d.lister.ListInstances(ctx)
+	cancel()
+	if err != nil {
+		log.Printf("gcpdial: polling %v: %v", d.lister, err)
+		return
+	}
+
+	want := map[string]bool{} // the res []string turned into a set
+	for _, instURL := range res {
+		want[instURL] = true
+	}
 
-		d.mu.Lock()
-		// Stop + remove any health check probers that no longer appear in the
-		// instance group.
-		for instURL, prober := range d.prober {
-			if !want[instURL] {
-				prober.cancel()
-				delete(d.prober, instURL)
-			}
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	// Stop + remove any health check probers that no longer appear in the
+	// instance group.
+	for instURL, prober := range d.prober {
+		if !want[instURL] {
+			prober.cancel()
+			delete(d.prober, instURL)
+		}
+	}
+	// And start any new health check probers that are newly added
+	// (or newly known at least) to the instance group.
+	for _, instURL := range res {
+		if _, ok := d.prober[instURL]; ok {
+			continue
 		}
-		// And start any new health check probers that are newly added
-		// (or newly known at least) to the instance group.
-		for _, instURL := range res {
-			if _, ok := d.prober[instURL]; ok {
-				continue
-			}
-			p := newProber(d, instURL)
-			go p.probeLoop()
-			if d.prober == nil {
-				d.prober = map[string]*prober{}
-			}
-			d.prober[instURL] = p
+		p := newProber(d, instURL)
+		go p.probeLoop()
+		if d.prober == nil {
+			d.prober = map[string]*prober{}
 		}
-		d.lastInstances = res
-		d.mu.Unlock()
+		d.prober[instURL] = p
 	}
+	d.lastInstances = res
 }
 
 // NewRegionInstanceGroupDialer returns a new dialer that dials named