mcimadamore@1562: /*
mcimadamore@1562:  * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
mcimadamore@1562:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
mcimadamore@1562:  *
mcimadamore@1562:  * This code is free software; you can redistribute it and/or modify it
mcimadamore@1562:  * under the terms of the GNU General Public License version 2 only, as
mcimadamore@1562:  * published by the Free Software Foundation.  Oracle designates this
mcimadamore@1562:  * particular file as subject to the "Classpath" exception as provided
mcimadamore@1562:  * by Oracle in the LICENSE file that accompanied this code.
mcimadamore@1562:  *
mcimadamore@1562:  * This code is distributed in the hope that it will be useful, but WITHOUT
mcimadamore@1562:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
mcimadamore@1562:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
mcimadamore@1562:  * version 2 for more details (a copy is included in the LICENSE file that
mcimadamore@1562:  * accompanied this code).
mcimadamore@1562:  *
mcimadamore@1562:  * You should have received a copy of the GNU General Public License version
mcimadamore@1562:  * 2 along with this work; if not, write to the Free Software Foundation,
mcimadamore@1562:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
mcimadamore@1562:  *
mcimadamore@1562:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
mcimadamore@1562:  * or visit www.oracle.com if you need additional information or have any
mcimadamore@1562:  * questions.
mcimadamore@1562:  */
mcimadamore@1562: 
mcimadamore@1562: package com.sun.tools.javac.util;
mcimadamore@1562: 
mcimadamore@1562: /** <p><b>This is NOT part of any supported API.
mcimadamore@1562:  *  If you write code that depends on this, you do so at your own risk.
mcimadamore@1562:  *  This code and its internal interfaces are subject to change or
mcimadamore@1562:  *  deletion without notice.</b>
mcimadamore@1562:  */
mcimadamore@1562: public class GraphUtils {
mcimadamore@1562: 
mcimadamore@1562:     /**
mcimadamore@1562:      * This class is a basic abstract class for representing a node.
mcimadamore@1562:      * A node is associated with a given data.
mcimadamore@1562:      */
mcimadamore@1562:     public static abstract class Node<D> {
mcimadamore@1562:         public final D data;
mcimadamore@1562: 
mcimadamore@1562:         public Node(D data) {
mcimadamore@1562:             this.data = data;
mcimadamore@1562:         }
mcimadamore@1562: 
mcimadamore@1562:         public abstract Iterable<? extends Node<D>> getDependencies();
mcimadamore@1562: 
mcimadamore@1562:         public abstract String printDependency(Node<D> to);
mcimadamore@1562: 
mcimadamore@1562:         @Override
mcimadamore@1562:         public String toString() {
mcimadamore@1562:             return data.toString();
mcimadamore@1562:         }
mcimadamore@1562:     }
mcimadamore@1562: 
mcimadamore@1562:     /**
mcimadamore@1562:      * This class specialized Node, by adding elements that are required in order
mcimadamore@1562:      * to perform Tarjan computation of strongly connected components.
mcimadamore@1562:      */
mcimadamore@1562:     public static abstract class TarjanNode<D> extends Node<D> implements Comparable<TarjanNode<D>> {
mcimadamore@1562:         int index = -1;
mcimadamore@1562:         int lowlink;
mcimadamore@1562:         boolean active;
mcimadamore@1562: 
mcimadamore@1562:         public TarjanNode(D data) {
mcimadamore@1562:             super(data);
mcimadamore@1562:         }
mcimadamore@1562: 
mcimadamore@1562:         public abstract Iterable<? extends TarjanNode<D>> getDependencies();
mcimadamore@1562: 
mcimadamore@1562:         public int compareTo(TarjanNode<D> o) {
mcimadamore@1562:             return (index < o.index) ? -1 : (index == o.index) ? 0 : 1;
mcimadamore@1562:         }
mcimadamore@1562:     }
mcimadamore@1562: 
mcimadamore@1562:     /**
mcimadamore@1562:      * Tarjan's algorithm to determine strongly connected components of a
mcimadamore@1562:      * directed graph in linear time. Works on TarjanNode.
mcimadamore@1562:      */
mcimadamore@1562:     public static <D, N extends TarjanNode<D>> List<? extends List<? extends N>> tarjan(Iterable<? extends N> nodes) {
mcimadamore@1562:         ListBuffer<List<N>> cycles = ListBuffer.lb();
mcimadamore@1562:         ListBuffer<N> stack = ListBuffer.lb();
mcimadamore@1562:         int index = 0;
mcimadamore@1562:         for (N node: nodes) {
mcimadamore@1562:             if (node.index == -1) {
mcimadamore@1562:                 index += tarjan(node, index, stack, cycles);
mcimadamore@1562:             }
mcimadamore@1562:         }
mcimadamore@1562:         return cycles.toList();
mcimadamore@1562:     }
mcimadamore@1562: 
mcimadamore@1562:     private static <D, N extends TarjanNode<D>> int tarjan(N v, int index, ListBuffer<N> stack, ListBuffer<List<N>> cycles) {
mcimadamore@1562:         v.index = index;
mcimadamore@1562:         v.lowlink = index;
mcimadamore@1562:         index++;
mcimadamore@1562:         stack.prepend(v);
mcimadamore@1562:         v.active = true;
mcimadamore@1562:         for (TarjanNode<D> nd: v.getDependencies()) {
mcimadamore@1562:             @SuppressWarnings("unchecked")
mcimadamore@1562:             N n = (N)nd;
mcimadamore@1562:             if (n.index == -1) {
mcimadamore@1562:                 tarjan(n, index, stack, cycles);
mcimadamore@1562:                 v.lowlink = Math.min(v.lowlink, n.lowlink);
mcimadamore@1562:             } else if (stack.contains(n)) {
mcimadamore@1562:                 v.lowlink = Math.min(v.lowlink, n.index);
mcimadamore@1562:             }
mcimadamore@1562:         }
mcimadamore@1562:         if (v.lowlink == v.index) {
mcimadamore@1562:             N n;
mcimadamore@1562:             ListBuffer<N> cycle = ListBuffer.lb();
mcimadamore@1562:             do {
mcimadamore@1562:                 n = stack.remove();
mcimadamore@1562:                 n.active = false;
mcimadamore@1562:                 cycle.add(n);
mcimadamore@1562:             } while (n != v);
mcimadamore@1562:             cycles.add(cycle.toList());
mcimadamore@1562:         }
mcimadamore@1562:         return index;
mcimadamore@1562:     }
mcimadamore@1562: 
mcimadamore@1562:     /**
mcimadamore@1562:      * Debugging: dot representation of a set of connected nodes. The resulting
mcimadamore@1562:      * dot representation will use {@code Node.toString} to display node labels
mcimadamore@1562:      * and {@code Node.printDependency} to display edge labels. The resulting
mcimadamore@1562:      * representation is also customizable with a graph name and a header.
mcimadamore@1562:      */
mcimadamore@1562:     public static <D> String toDot(Iterable<? extends TarjanNode<D>> nodes, String name, String header) {
mcimadamore@1562:         StringBuilder buf = new StringBuilder();
mcimadamore@1562:         buf.append(String.format("digraph %s {\n", name));
mcimadamore@1562:         buf.append(String.format("label = \"%s\";\n", header));
mcimadamore@1562:         //dump nodes
mcimadamore@1562:         for (TarjanNode<D> n : nodes) {
mcimadamore@1562:             buf.append(String.format("%s [label = \"%s\"];\n", n.hashCode(), n.toString()));
mcimadamore@1562:         }
mcimadamore@1562:         //dump arcs
mcimadamore@1562:         for (TarjanNode<D> from : nodes) {
mcimadamore@1562:             for (TarjanNode<D> to : from.getDependencies()) {
mcimadamore@1562:                 buf.append(String.format("%s -> %s [label = \" %s \"];\n",
mcimadamore@1562:                         from.hashCode(), to.hashCode(), from.printDependency(to)));
mcimadamore@1562:             }
mcimadamore@1562:         }
mcimadamore@1562:         buf.append("}\n");
mcimadamore@1562:         return buf.toString();
mcimadamore@1562:     }
mcimadamore@1562: }