DelayRevQueue.java

/*
 * Copyright (C) 2009, Google Inc.
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.revwalk;

import java.io.IOException;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;

/**
 * Delays commits to be at least {@link PendingGenerator#OVER_SCAN} late.
 * <p>
 * This helps to "fix up" weird corner cases resulting from clock skew, by
 * slowing down what we produce to the caller we get a better chance to ensure
 * PendingGenerator reached back far enough in the graph to correctly mark
 * commits {@link RevWalk#UNINTERESTING} if necessary.
 * <p>
 * This generator should appear before {@link FixUninterestingGenerator} if the
 * lower level {@link #pending} isn't already fully buffered.
 */
final class DelayRevQueue extends Generator {
    private static final int OVER_SCAN = PendingGenerator.OVER_SCAN;

    private final Generator pending;

    private final FIFORevQueue delay;

    private int size;

    DelayRevQueue(Generator g) {
        super(g.firstParent);
        pending = g;
        delay = new FIFORevQueue();
    }

    @Override
    int outputType() {
        return pending.outputType();
    }

    @Override
    RevCommit next() throws MissingObjectException,
            IncorrectObjectTypeException, IOException {
        while (size < OVER_SCAN) {
            final RevCommit c = pending.next();
            if (c == null)
                break;
            delay.add(c);
            size++;
        }

        final RevCommit c = delay.next();
        if (c == null)
            return null;
        size--;
        return c;
    }
}