use sync.Once instead of a mutex

Signed-off-by: Olga Shestopalova <[email protected]>

Author: olyazavr

pkg/volume/flexvolume/probe.go

@@ -40,6 +40,7 @@ type flexVolumeProber struct {
 	factory        PluginFactory
 	fs             utilfs.Filesystem
 	probeAllNeeded bool
+	probeAllOnce   sync.Once
 	eventsMap      map[string]volume.ProbeOperation // the key is the driver directory path, the value is the corresponding operation
 }
 
@@ -55,7 +56,7 @@ func GetDynamicPluginProber(pluginDir string, runner exec.Interface) volume.Dyna
 }
 
 func (prober *flexVolumeProber) Init() error {
-	prober.testAndSetProbeAllNeeded(true)
+	prober.probeAllNeeded = true
 	prober.eventsMap = map[string]volume.ProbeOperation{}
 
 	if err := prober.createPluginDir(); err != nil {
@@ -68,23 +69,18 @@ func (prober *flexVolumeProber) Init() error {
 	return nil
 }
 
-// If probeAllNeeded is true, probe all pluginDir
+// If we haven't yet done so, probe all pluginDir
 // else probe events in eventsMap
 func (prober *flexVolumeProber) Probe() (events []volume.ProbeEvent, err error) {
-	prober.mutex.RLock()
-	if prober.probeAllNeeded {
-		prober.mutex.RUnlock()
-		prober.mutex.Lock()
-		// check again, if multiple readers got through the first if, only one should probeAll
-		if prober.probeAllNeeded {
-			events, err = prober.probeAll()
-			prober.probeAllNeeded = false
-			prober.mutex.Unlock()
-			return
-		}
-		prober.mutex.Unlock()
+	probedAll := false
+	prober.probeAllOnce.Do(func() {
+		events, err = prober.probeAll()
+		probedAll = true
+		prober.probeAllNeeded = false
+	})
+	if probedAll {
+		return events, err
 	}
-	prober.mutex.RUnlock()
 	return prober.probeMap()
 }
 
@@ -287,10 +283,3 @@ func (prober *flexVolumeProber) createPluginDir() error {
 
 	return nil
 }
-
-func (prober *flexVolumeProber) testAndSetProbeAllNeeded(newval bool) (oldval bool) {
-	prober.mutex.Lock()
-	defer prober.mutex.Unlock()
-	oldval, prober.probeAllNeeded = prober.probeAllNeeded, newval
-	return
-}