JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2019, Red Hat, Inc. All rights reserved.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

package sun.jvm.hotspot.gc.shenandoah;

import sun.jvm.hotspot.utilities.BitMap;
import sun.jvm.hotspot.utilities.BitMapInterface;

import java.util.HashMap;

public class ShenandoahBitMap implements BitMapInterface {
    private HashMap<ShenandoahHeapRegion, BitMap> regionToBitMap = new HashMap<>();
    private ShenandoahHeap heap;

    ShenandoahBitMap(ShenandoahHeap heap) {
        this.heap = heap;
    }

    @Override
    public boolean at(long offset) {
        ShenandoahHeapRegion region = heap.regionAtOffset(offset);
        BitMap bitmap = regionToBitMap.get(region);
        if (bitmap == null) {
            return false;
        } else {
            int index = toBitMapOffset(offset, region);
            return bitmap.at(index);
        }
    }

    @Override
    public void atPut(long offset, boolean value) {
        ShenandoahHeapRegion region = heap.regionAtOffset(offset);
        BitMap bitmap = getOrAddBitMap(region);
        int index = toBitMapOffset(offset, region);
        bitmap.atPut(index, value);
    }

    @Override
    public void clear() {
        for (BitMap bitMap : regionToBitMap.values()) {
            bitMap.clear();
        }
    }

    private int toBitMapOffset(long offset, ShenandoahHeapRegion region) {
        long regionSize = ShenandoahHeapRegion.regionSizeBytes();
        long regionOffset = region.regionNumber() * regionSize;
        long offsetInRegion = offset - regionOffset;

        if (offsetInRegion < 0 || offsetInRegion >= regionSize) {
            throw new RuntimeException("Unexpected negative offset: " + offsetInRegion);
        }
        return (int)(offsetInRegion >>> heap.getLogMinObjAlignmentInBytes());
    }

    private BitMap getOrAddBitMap(ShenandoahHeapRegion region) {
        BitMap bitMap = regionToBitMap.get(region);
        if (bitMap == null) {
            long regionSize = ShenandoahHeapRegion.regionSizeBytes();
            long maxNumObjects = regionSize >>> heap.getLogMinObjAlignmentInBytes();

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