1 files changed, 98 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/actions/BipartiteVisitor.java b/src/main/java/com/google/devtools/build/lib/actions/BipartiteVisitor.java
new file mode 100644
index 0000000000..61803c8dd1
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/actions/BipartiteVisitor.java
@@ -0,0 +1,98 @@
+// 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.lib.actions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A visitor helper class for bipartite graphs.  The alternate kinds of nodes
+ * are arbitrarily designated "black" or "white".
+ *
+ * <p> Subclasses implement the black() and white() hook functions which are
+ * called as nodes are visited.  The class holds a mapping from each node to a
+ * small integer; this is available to subclasses if they wish.
+ */
+public abstract class BipartiteVisitor<BLACK, WHITE> {
+
+  protected BipartiteVisitor() {}
+
+  private int nextNodeId = 0;
+
+  // Maps each visited black node to a small integer.
+  protected final Map<BLACK, Integer> visitedBlackNodes = new HashMap<>();
+
+  // Maps each visited white node to a small integer.
+  protected final Map<WHITE, Integer> visitedWhiteNodes = new HashMap<>();
+
+  /**
+   *  Visit the specified black node.  If this node has not already been
+   *  visited, the black() hook is called and true is returned; otherwise,
+   *  false is returned.
+   */
+  public final boolean visitBlackNode(BLACK blackNode) {
+    if (blackNode == null) { throw new NullPointerException(); }
+    if (!visitedBlackNodes.containsKey(blackNode)) {
+      visitedBlackNodes.put(blackNode, nextNodeId++);
+      black(blackNode);
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Visit all specified black nodes.
+   */
+  public final void visitBlackNodes(Iterable<BLACK> blackNodes) {
+    for (BLACK blackNode : blackNodes) {
+      visitBlackNode(blackNode);
+    }
+  }
+
+  /**
+   *  Visit the specified white node.  If this node has not already been
+   *  visited, the white() hook is called and true is returned; otherwise,
+   *  false is returned.
+   */
+  public final boolean visitWhiteNode(WHITE whiteNode) {
+    if (whiteNode == null) {
+      throw new NullPointerException();
+    }
+    if (!visitedWhiteNodes.containsKey(whiteNode)) {
+      visitedWhiteNodes.put(whiteNode, nextNodeId++);
+      white(whiteNode);
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Visit all specified white nodes.
+   */
+  public final void visitWhiteNodes(Iterable<WHITE> whiteNodes) {
+    for (WHITE whiteNode : whiteNodes) {
+      visitWhiteNode(whiteNode);
+    }
+  }
+
+  /**
+   * Called whenever a white node is visited.  Hook for subclasses.
+   */
+  protected abstract void white(WHITE whiteNode);
+
+  /**
+   * Called whenever a black node is visited.  Hook for subclasses.
+   */
+  protected abstract void black(BLACK blackNode);
+}