Add interfaces for the build event protocol

Bazel in the will provide a machine-readable stream of important build
events. These interfaces set up the framework and expectations about
the produced events and the entities distributing those events.

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Change-Id: If2c3b2e11c31b0136b57eadeef2d2f8f8fe5e2e7
Reviewed-on: https://bazel-review.googlesource.com/#/c/6272
MOS_MIGRATED_REVID=134522369

1 files changed, 50 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/buildeventstream/ChainableEvent.java b/src/main/java/com/google/devtools/build/lib/buildeventstream/ChainableEvent.java
new file mode 100644
index 0000000000..3fdf22c3ba
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/buildeventstream/ChainableEvent.java
@@ -0,0 +1,50 @@
+// 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();
+}