Refactor the way that the that node_ping_controller works

This moves node ping controller to using the new internal lock
API.

The reason for this is twofold:
* The channel approach that was used to notify other
  controllers of changes could only be used once (at startup),
  and couldn't be used in the future to broadcast node
  ping status. The idea idea is here that we could move
  to a sync.Cond style API and only wakeup other controllers
  on change, as opposed to constantly polling each other
* The problem with sync.Cond is that it's not context friendly.
  If we want to do stuff like wait on a sync.cond and use a context
  or a timer or similar, it doesn't work whereas this API allows
  context cancellations on condition change.

The idea is that as we have more controllers that act as centralized
sources of authority, they can broadcast out their state.

internal/lock/monitor_test.go

@@ -0,0 +1,113 @@
+package lock
+
+import (
+	"sync"
+	"testing"
+	"time"
+
+	"golang.org/x/sync/errgroup"
+	"k8s.io/apimachinery/pkg/util/sets"
+
+	"gotest.tools/assert"
+	is "gotest.tools/assert/cmp"
+)
+
+func TestMonitorUninitialized(t *testing.T) {
+	t.Parallel()
+	mv := NewMonitorVariable()
+	subscription := mv.Subscribe()
+	select {
+	case <-subscription.NewValueReady():
+		t.Fatalf("Received value update message: %v", subscription.Value())
+	case <-time.After(time.Second):
+	}
+}
+
+func TestGetUninitialized(t *testing.T) {
+	mv := NewMonitorVariable()
+	subscription := mv.Subscribe()
+	val := subscription.Value()
+	assert.Assert(t, is.Equal(val.Version, int64(0)))
+}
+
+func TestMonitorSetInitialVersionAfterListen(t *testing.T) {
+	mv := NewMonitorVariable()
+	subscription := mv.Subscribe()
+	go mv.Set("test")
+	<-subscription.NewValueReady()
+	assert.Assert(t, is.Equal(subscription.Value().Value, "test"))
+}
+
+func TestMonitorSetInitialVersionBeforeListen(t *testing.T) {
+	mv := NewMonitorVariable()
+	subscription := mv.Subscribe()
+	mv.Set("test")
+	<-subscription.NewValueReady()
+	assert.Assert(t, is.Equal(subscription.Value().Value, "test"))
+}
+
+func TestMonitorMultipleVersionsBlock(t *testing.T) {
+	t.Parallel()
+	mv := NewMonitorVariable()
+	subscription := mv.Subscribe()
+	mv.Set("test")
+	<-subscription.NewValueReady()
+	/* This should mark the "current" version as seen */
+	val := subscription.Value()
+	assert.Assert(t, is.Equal(val.Version, int64(1)))
+	select {
+	case <-subscription.NewValueReady():
+		t.Fatalf("Received value update message: %v", subscription.Value())
+	case <-time.After(time.Second):
+	}
+}
+func TestMonitorMultipleVersions(t *testing.T) {
+	t.Parallel()
+	lock := sync.Mutex{}
+	lock.Lock()
+	mv := NewMonitorVariable()
+	triggers := []int{}
+	ch := make(chan struct{}, 10)
+	go func() {
+		defer lock.Unlock()
+		subscription := mv.Subscribe()
+		for {
+			select {
+			case <-subscription.NewValueReady():
+				val := subscription.Value()
+				triggers = append(triggers, val.Value.(int))
+				ch <- struct{}{}
+				if val.Value == 9 {
+					return
+				}
+			}
+
+		}
+	}()
+
+	for i := 0; i < 10; i++ {
+		mv.Set(i)
+		// Wait for the trigger to occur
+		<-ch
+	}
+
+	// Wait for the goroutine to finish
+	lock.Lock()
+	t.Logf("Saw %v triggers", triggers)
+	assert.Assert(t, is.Len(triggers, 10))
+	// Make sure we saw all 10 unique values
+	assert.Assert(t, is.Equal(sets.NewInt(triggers...).Len(), 10))
+}
+func TestMonitorMultipleSubscribers(t *testing.T) {
+	group := &errgroup.Group{}
+	mv := NewMonitorVariable()
+	for i := 0; i < 10; i++ {
+		sub := mv.Subscribe()
+		group.Go(func() error {
+			<-sub.NewValueReady()
+			return nil
+		})
+	}
+	mv.Set(1)
+	_ = group.Wait()
+}