Updated comments on internal abstractions in client-go/tools/cache

The comments on Store and Queue and the FIFOs ceased being accurate
long ago.

Kubernetes-commit: 7a7ccb797e0c977c8049c1490f5a1f92f0bfbbb2

tools/cache/store.go

@@ -23,27 +23,52 @@ import (
 	"k8s.io/apimachinery/pkg/api/meta"
 )
 
-// Store is a generic object storage interface. Reflector knows how to watch a server
-// and update a store. A generic store is provided, which allows Reflector to be used
-// as a local caching system, and an LRU store, which allows Reflector to work like a
-// queue of items yet to be processed.
+// Store is a generic object storage and processing interface.  A
+// Store holds a map from string keys to accumulators, and has
+// operations to add, update, and delete a given object to/from the
+// accumulator currently associated with a given key.  A Store also
+// knows how to extract the key from a given object, so many operations
+// are given only the object.
 //
-// Store makes no assumptions about stored object identity; it is the responsibility
-// of a Store implementation to provide a mechanism to correctly key objects and to
-// define the contract for obtaining objects by some arbitrary key type.
+// In the simplest Store implementations each accumulator is simply
+// the last given object and thus the Store's behavior is simple
+// storage.
+//
+// Reflector knows how to watch a server and update a Store.  This
+// package provides a variety of implementations of Store.
 type Store interface {
+
+	// Add adds the given object to the accumulator associated with the given object's key
 	Add(obj interface{}) error
+
+	// Update updates the given object in the accumulator associated with the given object's key
 	Update(obj interface{}) error
+
+	// Delete deletes the given object from the accumulator associated with the given object's key
 	Delete(obj interface{}) error
+
+	// List returns a list of all the currently non-empty accumulators
 	List() []interface{}
+
+	// ListKeys returns a list of all the keys currently associated with non-empty accumulators
 	ListKeys() []string
+
+	// Get returns the accumulator associated with the given object's key
 	Get(obj interface{}) (item interface{}, exists bool, err error)
+
+	// GetByKey returns the accumulator associated with the given key
 	GetByKey(key string) (item interface{}, exists bool, err error)
 
 	// Replace will delete the contents of the store, using instead the
 	// given list. Store takes ownership of the list, you should not reference
 	// it after calling this function.
 	Replace([]interface{}, string) error
+
+	// Resync is meaningless in the terms appearing here but has
+	// meaning in some implementations that have non-trivial
+	// additional behavior.  In general the idea is to tee up the
+	// current non-empty accumulators or their keys for
+	// reconsideration (whatever that means).
 	Resync() error
 }