com.facebook.buck.core.util.graph.AbstractBreadthFirstThrowingTraversal.java Source code

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Here is the source code for com.facebook.buck.core.util.graph.AbstractBreadthFirstThrowingTraversal.java

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/*
 * Copyright 2015-present Facebook, Inc.
 *
 * 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.facebook.buck.core.util.graph;

import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Set;

/** Performs a breadth-first traversal of dependencies of a graph node. */
public abstract class AbstractBreadthFirstThrowingTraversal<Node, E extends Throwable> {

    private final Queue<Node> toExplore;
    private final Set<Node> explored;

    public AbstractBreadthFirstThrowingTraversal(Node initialNode) {
        this(ImmutableSet.of(initialNode));
    }

    public AbstractBreadthFirstThrowingTraversal(Iterable<? extends Node> initialNodes) {
        toExplore = new LinkedList<>();
        Iterables.addAll(toExplore, initialNodes);
        explored = new HashSet<>();
    }

    public final void start() throws E {
        while (!toExplore.isEmpty()) {
            Node currentNode = toExplore.remove();
            if (explored.contains(currentNode)) {
                continue;
            }

            Iterable<? extends Node> depsToVisit = this.visit(currentNode);
            explored.add(currentNode);

            for (Node dep : depsToVisit) {
                if (!explored.contains(dep)) {
                    toExplore.add(dep);
                }
            }
        }

        this.onComplete();
    }

    /** Override this method with any logic that should be run when {@link #start()} completes. */
    protected void onComplete() throws E {
    }

    /**
     * To perform a full traversal of the the {@code initialNode}'s transitive dependencies, this
     * function should return all of {@code node}'s direct dependencies.
     *
     * @param node Visited graph node
     * @return The set of direct dependencies to visit after visiting this node.
     */
    public abstract Iterable<? extends Node> visit(Node node) throws E;

    /**
     * This will typically be implemented as a lambda passed to {@link #traverse(Object, Visitor)} or
     * {@link #traverse(Iterable, Visitor)}
     */
    public interface Visitor<Node, E extends Throwable> {
        Iterable<Node> visit(Node node) throws E;
    }

    protected static class StaticBreadthFirstTraversal<Node>
            extends AbstractBreadthFirstThrowingTraversal<Node, RuntimeException> {

        private final Visitor<Node, RuntimeException> visitor;

        protected StaticBreadthFirstTraversal(Node initialNode, Visitor<Node, RuntimeException> visitor) {
            super(initialNode);
            this.visitor = visitor;
        }

        protected StaticBreadthFirstTraversal(Iterable<? extends Node> initialNodes,
                Visitor<Node, RuntimeException> visitor) {
            super(initialNodes);
            this.visitor = visitor;
        }

        @Override
        public Iterable<Node> visit(Node node) throws RuntimeException {
            return visitor.visit(node);
        }
    }

    /**
     * Traverse a graph without explicitly creating a {@code new
     * AbstractBreadthFirstThrowingTraversal} and overriding {@link #visit(Object)}
     *
     * @param visitor Typically a lambda expression
     */
    public static <Node> void traverse(Node initialNode, Visitor<Node, RuntimeException> visitor) {
        new StaticBreadthFirstTraversal<>(initialNode, visitor).start();
    }

    /**
     * Traverse a graph without explicitly creating a {@code new
     * AbstractBreadthFirstThrowingTraversal} and overriding {@link #visit(Object)}
     *
     * @param visitor Typically a lambda expression
     */
    public static <Node> void traverse(Iterable<? extends Node> initialNodes,
            Visitor<Node, RuntimeException> visitor) {
        new StaticBreadthFirstTraversal<>(initialNodes, visitor).start();
    }
}