Refactor NodeEntry, create node representation without a value

This CL introduces a ThinNodeEntry, which is a NodeEntry without the
means of accessing its value. The InvalidatingNodeVisitor does not
need to access nodes' values while doing its work, so it is provided
with a ThinNodeQueryableGraph, capable of producing only
ThinNodeEntries.

--
MOS_MIGRATED_REVID=102088111

1 files changed, 40 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/skyframe/ThinNodeQueryableGraph.java b/src/main/java/com/google/devtools/build/skyframe/ThinNodeQueryableGraph.java
new file mode 100644
index 0000000000..7ad18e98fe
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/skyframe/ThinNodeQueryableGraph.java
@@ -0,0 +1,40 @@
+// Copyright 2014 Google Inc. 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.skyframe;
+
+import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
+
+import java.util.Map;
+
+import javax.annotation.Nullable;
+
+/**
+ * A graph that exposes thin representations of its entries and structure, for use by classes that
+ * must traverse it, but not read its entries' values.
+ */
+@ThreadSafe
+public interface ThinNodeQueryableGraph {
+  /**
+   * Returns the thin node with the given name, or {@code null} if the node does not exist.
+   */
+  @Nullable
+  ThinNodeEntry get(SkyKey key);
+
+  /**
+   * Fetches all the given thin nodes. Returns a map {@code m} such that, for all {@code k} in
+   * {@code keys}, {@code m.get(k).equals(e)} iff {@code get(k) == e} and {@code e != null}, and
+   * {@code !m.containsKey(k)} iff {@code get(k) == null}.
+   */
+  Map<SkyKey, ? extends ThinNodeEntry> getBatch(Iterable<SkyKey> keys);
+}