PendingGenerator.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;
import org.eclipse.jgit.errors.StopWalkException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.revwalk.filter.RevFilter;

/**
 * Default (and first pass) RevCommit Generator implementation for RevWalk.
 * <p>
 * This generator starts from a set of one or more commits and process them in
 * descending (newest to oldest) commit time order. Commits automatically cause
 * their parents to be enqueued for further processing, allowing the entire
 * commit graph to be walked. A {@link RevFilter} may be used to select a subset
 * of the commits and return them to the caller.
 */
class PendingGenerator extends Generator {
    private static final int PARSED = RevWalk.PARSED;

    private static final int SEEN = RevWalk.SEEN;

    private static final int UNINTERESTING = RevWalk.UNINTERESTING;

    /**
     * Number of additional commits to scan after we think we are done.
     * <p>
     * This small buffer of commits is scanned to ensure we didn't miss anything
     * as a result of clock skew when the commits were made. We need to set our
     * constant to 1 additional commit due to the use of a pre-increment
     * operator when accessing the value.
     */
    static final int OVER_SCAN = 5 + 1;

    /** A commit near the end of time, to initialize {@link #last} with. */
    private static final RevCommit INIT_LAST;

    static {
        INIT_LAST = new RevCommit(ObjectId.zeroId());
        INIT_LAST.commitTime = Integer.MAX_VALUE;
    }

    private final RevWalk walker;

    private final DateRevQueue pending;

    private final RevFilter filter;

    private final int output;

    /** Last commit produced to the caller from {@link #next()}. */
    private RevCommit last = INIT_LAST;

    /**
     * Number of commits we have remaining in our over-scan allotment.
     * <p>
     * Only relevant if there are {@link #UNINTERESTING} commits in the
     * {@link #pending} queue.
     */
    private int overScan = OVER_SCAN;

    boolean canDispose;

    PendingGenerator(final RevWalk w, final DateRevQueue p,
            final RevFilter f, final int out) {
        super(w.isFirstParent());
        walker = w;
        pending = p;
        filter = f;
        output = out;
        canDispose = true;
    }

    @Override
    int outputType() {
        return output | SORT_COMMIT_TIME_DESC;
    }

    @Override
    RevCommit next() throws MissingObjectException,
            IncorrectObjectTypeException, IOException {
        try {
            for (;;) {
                final RevCommit c = pending.next();
                if (c == null) {
                    return null;
                }

                final boolean produce;
                if ((c.flags & UNINTERESTING) != 0)
                    produce = false;
                else {
                    if (filter.requiresCommitBody())
                        c.parseBody(walker);
                    produce = filter.include(walker, c);
                }

                for (int i = 0; i < c.parents.length; i++) {
                    RevCommit p = c.parents[i];
                    // If the commit is uninteresting, don't try to prune
                    // parents because we want the maximal uninteresting set.
                    if (firstParent && i > 0 && (c.flags & UNINTERESTING) == 0) {
                        continue;
                    }
                    if ((p.flags & SEEN) != 0)
                        continue;
                    if ((p.flags & PARSED) == 0)
                        p.parseHeaders(walker);
                    p.flags |= SEEN;
                    pending.add(p);
                }
                walker.carryFlagsImpl(c);

                if ((c.flags & UNINTERESTING) != 0) {
                    if (pending.everbodyHasFlag(UNINTERESTING)) {
                        final RevCommit n = pending.peek();
                        if (n != null && n.commitTime >= last.commitTime) {
                            // This is too close to call. The next commit we
                            // would pop is dated after the last one produced.
                            // We have to keep going to ensure that we carry
                            // flags as much as necessary.
                            //
                            overScan = OVER_SCAN;
                        } else if (--overScan == 0)
                            throw StopWalkException.INSTANCE;
                    } else {
                        overScan = OVER_SCAN;
                    }
                    if (canDispose)
                        c.disposeBody();
                    continue;
                }

                if (produce)
                    return last = c;
                else if (canDispose)
                    c.disposeBody();
            }
        } catch (StopWalkException swe) {
            pending.clear();
            return null;
        }
    }
}