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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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package com.oracle.svm.core.heap;

import org.graalvm.compiler.word.Word;
import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;
import org.graalvm.word.Pointer;
import org.graalvm.word.UnsignedWord;

import com.oracle.svm.core.annotate.Uninterruptible;
import com.oracle.svm.core.hub.DynamicHub;
import com.oracle.svm.core.image.ImageHeapObject;
import com.oracle.svm.core.snippets.KnownIntrinsics;

An object header is a reference-sized collection of bits in each object instance. The object header holds a reference to a DynamicHub, which identifies the class of the instance. It may also contain a couple of reserved bits that encode internal state information (e.g., for the GC). During garbage collection, the object header may hold a forwarding reference to the new location of this instance if the object has been moved by the collector. /**
 * An object header is a reference-sized collection of bits in each object instance. The object
 * header holds a reference to a {@link DynamicHub}, which identifies the class of the instance. It
 * may also contain a couple of reserved bits that encode internal state information (e.g., for the
 * GC).
 *
 * During garbage collection, the object header may hold a forwarding reference to the new location
 * of this instance if the object has been moved by the collector.
 */
public abstract class ObjectHeader {
    @Platforms(Platform.HOSTED_ONLY.class)
    protected ObjectHeader() {
    }

    
Returns a mask where all reserved bits are set.
/**
     * Returns a mask where all reserved bits are set.
     */
    public abstract int getReservedBitsMask();

    public abstract long encodeAsImageHeapObjectHeader(ImageHeapObject obj, long hubOffsetFromHeapBase);

    public abstract Word encodeAsTLABObjectHeader(DynamicHub hub);

    public abstract Word encodeAsUnmanagedObjectHeader(DynamicHub hub);

    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
    public abstract DynamicHub dynamicHubFromObjectHeader(UnsignedWord header);

    public static DynamicHub readDynamicHubFromObject(Object o) {
        return KnownIntrinsics.readHub(o);
    }

    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
    public abstract DynamicHub readDynamicHubFromPointer(Pointer ptr);

    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
    public abstract void initializeHeaderOfNewObject(Pointer objectPointer, Word objectHeader);
}