Make sure at least one interrupt is buffered before dropping.

pkg/proxy/config/config.go

@@ -82,7 +82,11 @@ type EndpointsConfig struct {
 // NewEndpointsConfig creates a new EndpointsConfig.
 // It immediately runs the created EndpointsConfig.
 func NewEndpointsConfig() *EndpointsConfig {
-	updates := make(chan struct{})
+	// The updates channel is used to send interrupts to the Endpoints handler.
+	// It's buffered because we never want to block for as long as there is a
+	// pending interrupt, but don't want to drop them if the handler is doing
+	// work.
+	updates := make(chan struct{}, 1)
 	store := &endpointsStore{updates: updates, endpoints: make(map[string]map[types.NamespacedName]api.Endpoints)}
 	mux := config.NewMux(store)
 	bcaster := config.NewBroadcaster()
@@ -187,7 +191,11 @@ type ServiceConfig struct {
 // NewServiceConfig creates a new ServiceConfig.
 // It immediately runs the created ServiceConfig.
 func NewServiceConfig() *ServiceConfig {
-	updates := make(chan struct{})
+	// The updates channel is used to send interrupts to the Services handler.
+	// It's buffered because we never want to block for as long as there is a
+	// pending interrupt, but don't want to drop them if the handler is doing
+	// work.
+	updates := make(chan struct{}, 1)
 	store := &serviceStore{updates: updates, services: make(map[string]map[types.NamespacedName]api.Service)}
 	mux := config.NewMux(store)
 	bcaster := config.NewBroadcaster()

pkg/proxy/config/config_test.go

@@ -348,3 +348,8 @@ func TestNewMultipleSourcesEndpointsMultipleHandlersAddRemoveSetAndNotified(t *t
 	handler.ValidateEndpoints(t, endpoints)
 	handler2.ValidateEndpoints(t, endpoints)
 }
+
+// TODO: Add a unittest for interrupts getting processed in a timely manner.
+// Currently this module has a circular dependency with config, and so it's
+// named config_test, which means even test methods need to be public. This
+// is refactoring that we can avoid by resolving the dependency.