1 files changed, 59 insertions, 0 deletions
diff --git a/pkg/syncevent/source.go b/pkg/syncevent/source.go
new file mode 100644
index 000000000..ddffb171a
--- /dev/null
+++ b/pkg/syncevent/source.go
@@ -0,0 +1,59 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package syncevent
+
+// Source represents an event source.
+type Source interface {
+	// SubscribeEvents causes the Source to notify the given Receiver of the
+	// given subset of events.
+	//
+	// Preconditions: r != nil. The ReceiverCallback for r must not take locks
+	// that are ordered prior to the Source; for example, it cannot call any
+	// Source methods.
+	SubscribeEvents(r *Receiver, filter Set) SubscriptionID
+
+	// UnsubscribeEvents causes the Source to stop notifying the Receiver
+	// subscribed by a previous call to SubscribeEvents that returned the given
+	// SubscriptionID.
+	//
+	// Preconditions: UnsubscribeEvents may be called at most once for any
+	// given SubscriptionID.
+	UnsubscribeEvents(id SubscriptionID)
+}
+
+// SubscriptionID identifies a call to Source.SubscribeEvents.
+type SubscriptionID uint64
+
+// UnsubscribeAndAck is a convenience function that unsubscribes r from the
+// given events from src and also clears them from r.
+func UnsubscribeAndAck(src Source, r *Receiver, filter Set, id SubscriptionID) {
+	src.UnsubscribeEvents(id)
+	r.Ack(filter)
+}
+
+// NoopSource implements Source by never sending events to subscribed
+// Receivers.
+type NoopSource struct{}
+
+// SubscribeEvents implements Source.SubscribeEvents.
+func (NoopSource) SubscribeEvents(*Receiver, Set) SubscriptionID {
+	return 0
+}
+
+// UnsubscribeEvents implements Source.UnsubscribeEvents.
+func (NoopSource) UnsubscribeEvents(SubscriptionID) {
+}
+
+// See Broadcaster for a non-noop implementations of Source.