Change containerd monitor ticker to sleep

With the ticker this could end up just doing back-to-back checks, which
isn't really what we want here.
Instead use a sleep to ensure we actually sleep for the desired
interval.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

image/store_test.go

@@ -1,6 +1,7 @@
 package image // import "github.com/docker/docker/image"
 
 import (
+	"fmt"
 	"runtime"
 	"testing"
 
@@ -171,6 +172,20 @@ func TestGetAndSetLastUpdated(t *testing.T) {
 	assert.Equal(t, updated.IsZero(), false)
 }
 
+func TestStoreLen(t *testing.T) {
+	store, cleanup := defaultImageStore(t)
+	defer cleanup()
+
+	expected := 10
+	for i := 0; i < expected; i++ {
+		_, err := store.Create([]byte(fmt.Sprintf(`{"comment": "abc%d", "rootfs": {"type": "layers"}}`, i)))
+		assert.NoError(t, err)
+	}
+	numImages := store.Len()
+	assert.Equal(t, expected, numImages)
+	assert.Equal(t, len(store.Map()), numImages)
+}
+
 type mockLayerGetReleaser struct{}
 
 func (ls *mockLayerGetReleaser) Get(layer.ChainID) (layer.Layer, error) {

libcontainerd/remote_daemon.go

@@ -263,11 +263,15 @@ func (r *remote) startContainerd() error {
 func (r *remote) monitorConnection(monitor *containerd.Client) {
 	var transientFailureCount = 0
 
-	ticker := time.NewTicker(500 * time.Millisecond)
-	defer ticker.Stop()
-
 	for {
-		<-ticker.C
+		select {
+		case <-r.shutdownContext.Done():
+			r.logger.Info("stopping healthcheck following graceful shutdown")
+			monitor.Close()
+			return
+		case <-time.After(500 * time.Millisecond):
+		}
+
 		ctx, cancel := context.WithTimeout(r.shutdownContext, healthCheckTimeout)
 		_, err := monitor.IsServing(ctx)
 		cancel()