com.tencent.process.CyclicGraphDetector Maven / Gradle / Ivy

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package com.tencent.process;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.Stack;
import java.util.stream.Collectors;

// copy from jenkins 96a66619b55b3b78b86817798fe36e58b2798cd4

/**
 * Traverses a directed graph and if it contains any cycle, throw an exception.
 *
 * @author Kohsuke Kawaguchi
 */
public abstract class CyclicGraphDetector {
    private final Set visited = new HashSet<>();
    private final Set visiting = new HashSet<>();
    private final Stack path = new Stack<>();

    private final List topologicalOrder = new ArrayList<>();

    public void run(Iterable allNodes) throws CycleDetectedException {
        for (N n : allNodes) {
            visit(n);
        }
    }

    /**
     * Returns all the nodes in the topologically sorted order.
     * That is, if there's an edge a → b, b always come earlier than a.
     */
    public List getSorted() {
        return topologicalOrder;
    }

    /**
     * List up edges from the given node (by listing nodes that those edges point to.)
     *
     * @return
     *      Never null.
     */
    protected abstract Iterable getEdges(N n);

    private void visit(N p) throws CycleDetectedException {
        if (!visited.add(p))    return;

        visiting.add(p);
        path.push(p);
        for (N q : getEdges(p)) {
            if (q == null)        continue;   // ignore unresolved references
            if (visiting.contains(q))
                detectedCycle(q);
            visit(q);
        }
        visiting.remove(p);
        path.pop();
        topologicalOrder.add(p);
    }

    private void detectedCycle(N q) throws CycleDetectedException {
        int i = path.indexOf(q);
        path.push(q);
        reactOnCycle(q, path.subList(i, path.size()));
    }

    /**
     * React on detected cycles - default implementation throws an exception.
     */
    protected void reactOnCycle(N q, List cycle) throws CycleDetectedException {
        throw new CycleDetectedException(cycle);
    }

    public static final class CycleDetectedException extends Exception {
        public final List cycle;

        public CycleDetectedException(List cycle) {
            super("Cycle detected: " + cycle.stream().map(Object::toString).collect(Collectors.joining(" -> ")));
            this.cycle = cycle;
        }
    }
}