Merge pull request #59159 from roycaihw/dfifo

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Add comments about potential race in delta fifo

**What this PR does / why we need it**:

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

/sig api-machinery

Kubernetes-commit: 0394ffba6de860ece173a9a485d3518d3a8d37f2

Godeps/Godeps.json

@@ -248,331 +248,331 @@
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 			"ImportPath": "k8s.io/apimachinery/pkg/util/validation/field",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/pkg/util/wait",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/pkg/util/yaml",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/pkg/version",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/pkg/watch",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/third_party/forked/golang/json",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/third_party/forked/golang/netutil",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/apimachinery/third_party/forked/golang/reflect",
-      "Rev": "69f93cfab5c1d87f2cbd5e6631af8268b7f5542b"
+			"Rev": "67f813598630f41e59978aafdcf0af33fe02b117"
 		},
 		{
 			"ImportPath": "k8s.io/kube-openapi/pkg/util/proto",

tools/cache/delta_fifo.go

@@ -38,9 +38,22 @@ import (
 // TODO: consider merging keyLister with this object, tracking a list of
 //       "known" keys when Pop() is called. Have to think about how that
 //       affects error retrying.
-// TODO(lavalamp): I believe there is a possible race only when using an
+// NOTE: It is possible to misuse this and cause a race when using an
-//                 external known object source that the above TODO would
+//       external known object source.
-//                 fix.
+//       Whether there is a potential race depends on how the comsumer
+//       modifies knownObjects. In Pop(), process function is called under
+//       lock, so it is safe to update data structures in it that need to be
+//       in sync with the queue (e.g. knownObjects).
+//
+//       Example:
+//       In case of sharedIndexInformer being a consumer
+//       (https://github.com/kubernetes/kubernetes/blob/0cdd940f/staging/
+//       src/k8s.io/client-go/tools/cache/shared_informer.go#L192),
+//       there is no race as knownObjects (s.indexer) is modified safely
+//       under DeltaFIFO's lock. The only exceptions are GetStore() and
+//       GetIndexer() methods, which expose ways to modify the underlying
+//       storage. Currently these two methods are used for creating Lister
+//       and internal tests.
 //
 // Also see the comment on DeltaFIFO.
 func NewDeltaFIFO(keyFunc KeyFunc, knownObjects KeyListerGetter) *DeltaFIFO {
@@ -199,8 +212,6 @@ func (f *DeltaFIFO) Delete(obj interface{}) error {
 		if err == nil && !exists && !itemsExist {
 			// Presumably, this was deleted when a relist happened.
 			// Don't provide a second report of the same deletion.
-			// TODO(lavalamp): This may be racy-- we aren't properly locked
-			// with knownObjects.
 			return nil
 		}
 	}
@@ -485,8 +496,6 @@ func (f *DeltaFIFO) Replace(list []interface{}, resourceVersion string) error {
 	}
 
 	// Detect deletions not already in the queue.
-	// TODO(lavalamp): This may be racy-- we aren't properly locked
-	// with knownObjects. Unproven.
 	knownKeys := f.knownObjects.ListKeys()
 	queuedDeletions := 0
 	for _, k := range knownKeys {