// Copyright 2016 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.buildeventstream;
import java.util.Collection;
/**
* Interface for objects organised in a DAG-like fashion.
*
* <p>When objects that are naturally organised in a directed acyclic graph are sent sequentially
* over some channel, the graph-structure needs to represented in some way. We chose the
* representation that each node knows its immediate sucessor nodes (rather than its predecessors)
* to suit the * properties of the event stream: new parents of a node might be discovered late,
* e.g., if a test suite is only expanded after one of its tests is already finished as it was also
* needed for another target.
*/
public interface ChainableEvent {
/**
* Provide the identifier of the event.
*
* <p>Event identifiers have to be unique within the set of events belonging to the same build
* invocation.
*/
BuildEventId getEventId();
/**
* Provide the children of the event.
*
* <p>It is a requirement of a well-formed event stream that for every event that does not
* indicate the beginning of a new build, at least one parent be present before the event itself.
* However, more parents might appear later in the stream (e.g., if a test suite expanded later
* discovers that a test that is already completed belongs to it).
*
* <p>A build-event stream is finished if and only if all announced children have occurred.
*/
Collection<BuildEventId> getChildrenEvents();
}