Shrink mutation detection critical section

Author: liggitt

staging/src/k8s.io/client-go/tools/cache/mutation_detector.go

@@ -68,7 +68,13 @@ type defaultCacheMutationDetector struct {
 	name   string
 	period time.Duration
 
-	lock       sync.Mutex
+	// compareLock ensures only a single call to CompareObjects runs at a time
+	compareObjectsLock sync.Mutex
+
+	// addLock guards addedObjs between AddObject and CompareObjects
+	addedObjsLock sync.Mutex
+	addedObjs     []cacheObj
+
 	cachedObjs []cacheObj
 
 	retainDuration     time.Duration
@@ -118,15 +124,22 @@ func (d *defaultCacheMutationDetector) AddObject(obj interface{}) {
 	if obj, ok := obj.(runtime.Object); ok {
 		copiedObj := obj.DeepCopyObject()
 
-		d.lock.Lock()
-		defer d.lock.Unlock()
-		d.cachedObjs = append(d.cachedObjs, cacheObj{cached: obj, copied: copiedObj})
+		d.addedObjsLock.Lock()
+		defer d.addedObjsLock.Unlock()
+		d.addedObjs = append(d.addedObjs, cacheObj{cached: obj, copied: copiedObj})
 	}
 }
 
 func (d *defaultCacheMutationDetector) CompareObjects() {
-	d.lock.Lock()
-	defer d.lock.Unlock()
+	d.compareObjectsLock.Lock()
+	defer d.compareObjectsLock.Unlock()
+
+	// move addedObjs into cachedObjs under lock
+	// this keeps the critical section small to avoid blocking AddObject while we compare cachedObjs
+	d.addedObjsLock.Lock()
+	d.cachedObjs = append(d.cachedObjs, d.addedObjs...)
+	d.addedObjs = nil
+	d.addedObjsLock.Unlock()
 
 	altered := false
 	for i, obj := range d.cachedObjs {