fix for flux plugin: combine two separate code paths for populating t…

…he cache in resync() scenario and regular case #4117  (#4276)

* attempt #2

* small DRYing in unit tests

* step 2

* step 3

* michael's feedback

cmd/kubeapps-apis/plugins/fluxv2/packages/v1alpha1/cache/chart_cache.go

@@ -63,7 +63,7 @@ type ChartCache struct {
 	// significant in that it flushes the whole redis cache and re-populates the state from k8s.
 	// When that happens we don't really want any concurrent access to the cache until the resync()
 	// operation is complete. In other words, we want to:
-	//  - be able to have multiple concurrent readers (goroutines doing GetForOne()/GetForMultiple())
+	//  - be able to have multiple concurrent readers (goroutines doing GetForOne())
 	//  - only a single writer (goroutine doing a resync()) is allowed, and while its doing its job
 	//    no readers are allowed
 	resyncCond *sync.Cond

cmd/kubeapps-apis/plugins/fluxv2/packages/v1alpha1/cache/rate_limiting_queue.go

@@ -17,6 +17,10 @@ import (
 	log "k8s.io/klog/v2"
 )
 
+// Inspired by https://github.com/kubernetes/client-go/blob/master/util/workqueue/queue.go and
+//         by https://github.com/kubernetes/client-go/blob/v0.22.4/util/workqueue/rate_limiting_queue.go
+//	but adds a few funcs, like Name(), ExpectAdd(), WaitUntilForgotten() and Reset()
+
 // RateLimitingInterface is an interface that rate limits items being added to the queue.
 type RateLimitingInterface interface {
 	workqueue.RateLimitingInterface
@@ -83,19 +87,17 @@ func (q *rateLimitingType) Reset() {
 
 	q.queue.reset()
 
-	// this way we "forget" about ratelimit failures
+	// this way we "forget" about ratelimit failures, i.e. the items queued up
+	// via previous call(s) to .AddRateLimited() (i.e. via q.DelayingInterface.AddAfter)
 	q.rateLimiter = workqueue.DefaultControllerRateLimiter()
-
-	// TODO (gfichtenholt) Also need to "forget" the items queued up via previous call(s)
-	// to .AddRateLimited() (i.e. via q.DelayingInterface.AddAfter) ?
 }
 
 // only used in unit tests
 func (q *rateLimitingType) ExpectAdd(item string) {
 	q.queue.expectAdd(item)
 }
 
-// used in unit test and production code, when a repo/chart needs to be loaded on demand
+// used in unit test AND production code, when a repo/chart needs to be loaded on demand
 func (q *rateLimitingType) WaitUntilForgotten(item string) {
 	q.queue.waitUntilDone(item)
 	// q.queue might be done with the item, but it may have been