hooks: make hooks manager a singleton

This will make it easier to use it from various places of kubevirt
without a need to pass the manager everywhere or recollect sidecar
sockets.

cmd/virt-launcher/virt-launcher.go

@@ -266,9 +266,10 @@ func main() {
 	log.InitializeLogging("virt-launcher")
 
 	// Block until all requested hookSidecars are ready
-	if *requestedHooks != 0 {
-		hookManager := hooks.NewManager()
-		hookManager.Collect(*requestedHooks)
+	hookManager := hooks.GetManager()
+	err := hookManager.Collect(*requestedHooks)
+	if err != nil {
+		panic(err)
 	}
 
 	vm := v1.NewVMIReferenceFromNameWithNS(*namespace, *name)

pkg/hooks/manager.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"google.golang.org/grpc"
@@ -23,12 +24,19 @@ type hookClient struct {
 	hookPoints []*hooksInfo.HookPoint
 }
 
+var manager *Manager
+var once sync.Once
+
 type Manager struct {
+	collected             bool
 	callbacksPerHookPoint map[string][]*hookClient
 }
 
-func NewManager() *Manager {
-	return &Manager{}
+func GetManager() *Manager {
+	once.Do(func() {
+		manager = &Manager{collected: false}
+	})
+	return manager
 }
 
 func (m *Manager) Collect(numberOfRequestedHookSidecars uint) error {
@@ -41,6 +49,7 @@ func (m *Manager) Collect(numberOfRequestedHookSidecars uint) error {
 	sortCallbacksPerHookPoint(callbacksPerHookPoint)
 	log.Log.Infof("Sorted all collected sidecar sockets per hook point based on their priority and name: %v", callbacksPerHookPoint)
 
+	m.collected = true
 	m.callbacksPerHookPoint = callbacksPerHookPoint
 
 	return nil