content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.arrow.vector.complex;
  
  import static java.util.Collections.singletonList;
  import static org.apache.arrow.memory.util.LargeMemoryUtil.capAtMaxInt;
  import static org.apache.arrow.memory.util.LargeMemoryUtil.checkedCastToInt;
  import static org.apache.arrow.util.Preconditions.checkArgument;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  import org.apache.arrow.memory.ArrowBuf;
  import org.apache.arrow.memory.BufferAllocator;
  import org.apache.arrow.memory.OutOfMemoryException;
  import org.apache.arrow.memory.util.ArrowBufPointer;
  import org.apache.arrow.memory.util.ByteFunctionHelpers;
  import org.apache.arrow.memory.util.CommonUtil;
  import org.apache.arrow.memory.util.hash.ArrowBufHasher;
  import org.apache.arrow.util.Preconditions;
  import org.apache.arrow.vector.AddOrGetResult;
  import org.apache.arrow.vector.BitVectorHelper;
  import org.apache.arrow.vector.BufferBacked;
  import org.apache.arrow.vector.FieldVector;
  import org.apache.arrow.vector.ValueIterableVector;
  import org.apache.arrow.vector.ValueVector;
  import org.apache.arrow.vector.ZeroVector;
  import org.apache.arrow.vector.compare.VectorVisitor;
  import org.apache.arrow.vector.complex.impl.ComplexCopier;
  import org.apache.arrow.vector.complex.impl.ExtensionTypeWriterFactory;
  import org.apache.arrow.vector.complex.impl.UnionListViewReader;
  import org.apache.arrow.vector.complex.impl.UnionListViewWriter;
  import org.apache.arrow.vector.complex.reader.FieldReader;
  import org.apache.arrow.vector.complex.writer.FieldWriter;
  import org.apache.arrow.vector.ipc.message.ArrowFieldNode;
  import org.apache.arrow.vector.types.Types.MinorType;
  import org.apache.arrow.vector.types.pojo.ArrowType;
  import org.apache.arrow.vector.types.pojo.Field;
  import org.apache.arrow.vector.types.pojo.FieldType;
  import org.apache.arrow.vector.util.CallBack;
  import org.apache.arrow.vector.util.JsonStringArrayList;
  import org.apache.arrow.vector.util.OversizedAllocationException;
  import org.apache.arrow.vector.util.TransferPair;
  
  /**
   * A list view vector contains lists of a specific type of elements. Its structure contains four
   * elements.
   *
   * <ol>
   *   <li>A validity buffer.
   *   <li>An offset buffer, that denotes lists starts.
   *   <li>A size buffer, that denotes lists ends.
   *   <li>A child data vector that contains the elements of lists.
   * </ol>
   *
   * The latter three are managed by its superclass.
   */
  
  /*
   * TODO: consider merging the functionality in `BaseRepeatedValueVector` into this class.
   */
  public class ListViewVector extends BaseRepeatedValueViewVector
      implements PromotableVector, ValueIterableVector<List<?>> {
  
    protected UnionListViewReader reader;
    private CallBack callBack;
    protected Field field;
    protected int validityAllocationSizeInBytes;
  
    public static ListViewVector empty(String name, BufferAllocator allocator) {
      return new ListViewVector(
          name, allocator, FieldType.nullable(ArrowType.ListView.INSTANCE), null);
    }
  
    /**
     * Constructs a new instance.
     *
     * @param name The name of the instance.
     * @param allocator The allocator to use for allocating/reallocating buffers.
     * @param fieldType The type of this list.
     * @param callBack A schema change callback.
     */
    public ListViewVector(
        String name, BufferAllocator allocator, FieldType fieldType, CallBack callBack) {
      this(new Field(name, fieldType, null), allocator, callBack);
    }
  
    /**
     * Constructs a new instance.
     *
     * @param field The field materialized by this vector.
     * @param allocator The allocator to use for allocating/reallocating buffers.
     * @param callBack A schema change callback.
     */
    public ListViewVector(Field field, BufferAllocator allocator, CallBack callBack) {
      super(field.getName(), allocator, callBack);
      this.validityBuffer = allocator.getEmpty();
      this.field = field;
      this.callBack = callBack;
      this.validityAllocationSizeInBytes =
          BitVectorHelper.getValidityBufferSizeFromCount(INITIAL_VALUE_ALLOCATION);
    }
  
    @Override
    public void initializeChildrenFromFields(List<Field> children) {
      checkArgument(
          children.size() == 1,
          "ListViews have one child Field. Found: %s",
          children.isEmpty() ? "none" : children);
  
      Field field = children.get(0);
      AddOrGetResult<FieldVector> addOrGetVector = addOrGetVector(field.getFieldType());
      checkArgument(
          addOrGetVector.isCreated(), "Child vector already existed: %s", addOrGetVector.getVector());
  
      addOrGetVector.getVector().initializeChildrenFromFields(field.getChildren());
      this.field = new Field(this.field.getName(), this.field.getFieldType(), children);
    }
  
    @Override
    public void setInitialCapacity(int numRecords) {
      validityAllocationSizeInBytes = BitVectorHelper.getValidityBufferSizeFromCount(numRecords);
      super.setInitialCapacity(numRecords);
    }
  
    /**
     * Specialized version of setInitialCapacity() for ListViewVector. This is used by some callers
     * when they want to explicitly control and be conservative about memory allocated for inner data
     * vector. This is very useful when we are working with memory constraints for a query and have a
     * fixed amount of memory reserved for the record batch. In such cases, we are likely to face OOM
     * or related problems when we reserve memory for a record batch with value count x and do
     * setInitialCapacity(x) such that each vector allocates only what is necessary and not the
     * default amount, but the multiplier forces the memory requirement to go beyond what was needed.
     *
     * @param numRecords value count
     * @param density density of ListViewVector. Density is the average size of a list per position in
     *     the ListViewVector. For example, a density value of 10 implies each position in the list
     *     vector has a list of 10 values. A density value of 0.1 implies out of 10 positions in the
     *     list vector, 1 position has a list of size 1, and the remaining positions are null (no
     *     lists) or empty lists. This helps in tightly controlling the memory we provision for inner
     *     data vector.
     */
    @Override
    public void setInitialCapacity(int numRecords, double density) {
      validityAllocationSizeInBytes = BitVectorHelper.getValidityBufferSizeFromCount(numRecords);
      super.setInitialCapacity(numRecords, density);
    }
  
    /**
     * Specialized version of setInitialTotalCapacity() for ListViewVector. This is used by some
     * callers when they want to explicitly control and be conservative about memory allocated for
     * inner data vector. This is very useful when we are working with memory constraints for a query
     * and have a fixed amount of memory reserved for the record batch. In such cases, we are likely
     * to face OOM or related problems when we reserve memory for a record batch with value count x
     * and do setInitialCapacity(x) such that each vector allocates only what is necessary and not the
     * default amount, but the multiplier forces the memory requirement to go beyond what was needed.
     *
     * @param numRecords value count
     * @param totalNumberOfElements the total number of elements to allow for in this vector across
     *     all records.
     */
    @Override
    public void setInitialTotalCapacity(int numRecords, int totalNumberOfElements) {
      validityAllocationSizeInBytes = BitVectorHelper.getValidityBufferSizeFromCount(numRecords);
      super.setInitialTotalCapacity(numRecords, totalNumberOfElements);
    }
  
    @Override
    public List<FieldVector> getChildrenFromFields() {
      return singletonList(getDataVector());
    }
  
    /**
     * Load the buffers associated with this Field.
     *
     * @param fieldNode the fieldNode
     * @param ownBuffers the buffers for this Field (own buffers only, children not included)
     */
    @Override
    public void loadFieldBuffers(ArrowFieldNode fieldNode, List<ArrowBuf> ownBuffers) {
      if (ownBuffers.size() != 3) {
        throw new IllegalArgumentException(
            "Illegal buffer count, expected " + 3 + ", got: " + ownBuffers.size());
      }
  
      ArrowBuf bitBuffer = ownBuffers.get(0);
      ArrowBuf offBuffer = ownBuffers.get(1);
      ArrowBuf szBuffer = ownBuffers.get(2);
  
      validityBuffer.getReferenceManager().release();
      validityBuffer = BitVectorHelper.loadValidityBuffer(fieldNode, bitBuffer, allocator);
      offsetBuffer.getReferenceManager().release();
      offsetBuffer = offBuffer.getReferenceManager().retain(offBuffer, allocator);
      sizeBuffer.getReferenceManager().release();
      sizeBuffer = szBuffer.getReferenceManager().retain(szBuffer, allocator);
  
      validityAllocationSizeInBytes = checkedCastToInt(validityBuffer.capacity());
      offsetAllocationSizeInBytes = offsetBuffer.capacity();
      sizeAllocationSizeInBytes = sizeBuffer.capacity();
  
      valueCount = fieldNode.getLength();
    }
  
    /** Set the reader and writer indexes for the inner buffers. */
    private void setReaderAndWriterIndex() {
      validityBuffer.readerIndex(0);
      offsetBuffer.readerIndex(0);
      sizeBuffer.readerIndex(0);
      if (valueCount == 0) {
        validityBuffer.writerIndex(0);
        offsetBuffer.writerIndex(0);
        sizeBuffer.writerIndex(0);
      } else {
        validityBuffer.writerIndex(BitVectorHelper.getValidityBufferSizeFromCount(valueCount));
        offsetBuffer.writerIndex(valueCount * OFFSET_WIDTH);
        sizeBuffer.writerIndex(valueCount * SIZE_WIDTH);
      }
    }
  
    @Override
    public List<ArrowBuf> getFieldBuffers() {
      List<ArrowBuf> result = new ArrayList<>(2);
      setReaderAndWriterIndex();
      result.add(validityBuffer);
      result.add(offsetBuffer);
      result.add(sizeBuffer);
  
      return result;
    }
  
    /**
     * Export the buffers of the fields for C Data Interface. This method traverses the buffers and
     * export buffer and buffer's memory address into a list of buffers and a pointer to the list of
     * buffers.
     */
    @Override
    public void exportCDataBuffers(List<ArrowBuf> buffers, ArrowBuf buffersPtr, long nullValue) {
      exportBuffer(validityBuffer, buffers, buffersPtr, nullValue, true);
      exportBuffer(offsetBuffer, buffers, buffersPtr, nullValue, true);
      exportBuffer(sizeBuffer, buffers, buffersPtr, nullValue, true);
    }
  
    @Override
    public void allocateNew() throws OutOfMemoryException {
      if (!allocateNewSafe()) {
        throw new OutOfMemoryException("Failure while allocating memory");
      }
    }
  
    @Override
    public boolean allocateNewSafe() {
      boolean success = false;
      try {
        /* release the current buffers, hence this is a new allocation
         * Note that, the `clear` method call below is releasing validityBuffer
         * calling the superclass clear method which is releasing the associated buffers
         * (sizeBuffer and offsetBuffer).
         */
        clear();
        /* allocate validity buffer */
        allocateValidityBuffer(validityAllocationSizeInBytes);
        /* allocate offset, data and sizes buffer */
        success = super.allocateNewSafe();
      } finally {
        if (!success) {
          clear();
        }
      }
      return success;
    }
  
    @Override
    protected void allocateValidityBuffer(final long size) {
      super.allocateValidityBuffer(size);
      validityAllocationSizeInBytes = (int) size;
    }
  
    @Override
    public void reAlloc() {
      /* reallocate the validity buffer */
      reallocValidityBuffer();
      /* reallocate the offset, size, and data */
      super.reAlloc();
    }
  
    protected void reallocValidityAndSizeAndOffsetBuffers() {
      reallocateBuffers();
      reallocValidityBuffer();
    }
  
    private void reallocValidityBuffer() {
      final int currentBufferCapacity = checkedCastToInt(validityBuffer.capacity());
      long newAllocationSize = getNewAllocationSize(currentBufferCapacity);
  
      final ArrowBuf newBuf = allocator.buffer(newAllocationSize);
      newBuf.setBytes(0, validityBuffer, 0, currentBufferCapacity);
      newBuf.setZero(currentBufferCapacity, newBuf.capacity() - currentBufferCapacity);
      validityBuffer.getReferenceManager().release(1);
      validityBuffer = newBuf;
      validityAllocationSizeInBytes = (int) newAllocationSize;
    }
  
    private long getNewAllocationSize(int currentBufferCapacity) {
      long newAllocationSize = currentBufferCapacity * 2L;
      if (newAllocationSize == 0) {
        if (validityAllocationSizeInBytes > 0) {
          newAllocationSize = validityAllocationSizeInBytes;
        } else {
          newAllocationSize =
              BitVectorHelper.getValidityBufferSizeFromCount(INITIAL_VALUE_ALLOCATION) * 2L;
        }
      }
      newAllocationSize = CommonUtil.nextPowerOfTwo(newAllocationSize);
      assert newAllocationSize >= 1;
  
      if (newAllocationSize > MAX_ALLOCATION_SIZE) {
        throw new OversizedAllocationException("Unable to expand the buffer");
      }
      return newAllocationSize;
    }
  
    @Override
    public void copyFromSafe(int inIndex, int outIndex, ValueVector from) {
      copyFrom(inIndex, outIndex, from);
    }
  
    @Override
    public void copyFromSafe(
        int inIndex, int outIndex, ValueVector from, ExtensionTypeWriterFactory writerFactory) {
      copyFrom(inIndex, outIndex, from, writerFactory);
    }
  
    @Override
    public <OUT, IN> OUT accept(VectorVisitor<OUT, IN> visitor, IN value) {
      return visitor.visit(this, value);
    }
  
    @Override
    public void copyFrom(int inIndex, int outIndex, ValueVector from) {
      copyFrom(inIndex, outIndex, from, null);
    }
  
    @Override
    public void copyFrom(
        int inIndex, int outIndex, ValueVector from, ExtensionTypeWriterFactory writerFactory) {
      Preconditions.checkArgument(this.getMinorType() == from.getMinorType());
      FieldReader in = from.getReader();
      in.setPosition(inIndex);
      FieldWriter out = getWriter();
      out.setPosition(outIndex);
      ComplexCopier.copy(in, out, writerFactory);
    }
  
    @Override
    public FieldVector getDataVector() {
      return vector;
    }
  
    @Override
    public TransferPair getTransferPair(String ref, BufferAllocator allocator) {
      return getTransferPair(ref, allocator, null);
    }
  
    @Override
    public TransferPair getTransferPair(Field field, BufferAllocator allocator) {
      return getTransferPair(field, allocator, null);
    }
  
    @Override
    public TransferPair getTransferPair(String ref, BufferAllocator allocator, CallBack callBack) {
      return new TransferImpl(ref, allocator, callBack);
    }
  
    @Override
    public TransferPair getTransferPair(Field field, BufferAllocator allocator, CallBack callBack) {
      return new TransferImpl(field, allocator, callBack);
    }
  
    @Override
    public TransferPair makeTransferPair(ValueVector target) {
      return new TransferImpl((ListViewVector) target);
    }
  
    @Override
    public long getValidityBufferAddress() {
      return validityBuffer.memoryAddress();
    }
  
    @Override
    public long getDataBufferAddress() {
      throw new UnsupportedOperationException();
    }
  
    @Override
    public long getOffsetBufferAddress() {
      return offsetBuffer.memoryAddress();
    }
  
    @Override
    public ArrowBuf getValidityBuffer() {
      return validityBuffer;
    }
  
    @Override
    public ArrowBuf getDataBuffer() {
      throw new UnsupportedOperationException();
    }
  
    @Override
    public ArrowBuf getOffsetBuffer() {
      return offsetBuffer;
    }
  
    public ArrowBuf getSizeBuffer() {
      return sizeBuffer;
    }
  
    public long getSizeBufferAddress() {
      return sizeBuffer.memoryAddress();
    }
  
    /**
     * Get the hash code for the element at the given index.
     *
     * @param index position of the element
     * @return hash code for the element at the given index
     */
    @Override
    public int hashCode(int index) {
      return hashCode(index, null);
    }
  
    /**
     * Get the hash code for the element at the given index.
     *
     * @param index position of the element
     * @param hasher hasher to use
     * @return hash code for the element at the given index
     */
    @Override
    public int hashCode(int index, ArrowBufHasher hasher) {
      if (isSet(index) == 0) {
        return ArrowBufPointer.NULL_HASH_CODE;
      }
      int hash = 0;
      final int start = offsetBuffer.getInt(index * OFFSET_WIDTH);
      final int end = sizeBuffer.getInt(index * OFFSET_WIDTH);
      for (int i = start; i < end; i++) {
        hash = ByteFunctionHelpers.combineHash(hash, vector.hashCode(i, hasher));
      }
      return hash;
    }
  
    private class TransferImpl implements TransferPair {
  
      ListViewVector to;
      TransferPair dataTransferPair;
  
      public TransferImpl(String name, BufferAllocator allocator, CallBack callBack) {
        this(new ListViewVector(name, allocator, field.getFieldType(), callBack));
      }
  
      public TransferImpl(Field field, BufferAllocator allocator, CallBack callBack) {
        this(new ListViewVector(field, allocator, callBack));
      }
  
      public TransferImpl(ListViewVector to) {
        this.to = to;
        to.addOrGetVector(vector.getField().getFieldType());
        if (to.getDataVector() instanceof ZeroVector) {
          to.addOrGetVector(vector.getField().getFieldType());
        }
        dataTransferPair = getDataVector().makeTransferPair(to.getDataVector());
      }
  
      @Override
      public void transfer() {
        to.clear();
        dataTransferPair.transfer();
        to.validityBuffer = transferBuffer(validityBuffer, to.allocator);
        to.offsetBuffer = transferBuffer(offsetBuffer, to.allocator);
        to.sizeBuffer = transferBuffer(sizeBuffer, to.allocator);
        if (valueCount > 0) {
          to.setValueCount(valueCount);
        }
        clear();
      }
  
      @Override
      public void splitAndTransfer(int startIndex, int length) {
        Preconditions.checkArgument(
            startIndex >= 0 && length >= 0 && startIndex + length <= valueCount,
            "Invalid parameters startIndex: %s, length: %s for valueCount: %s",
            startIndex,
            length,
            valueCount);
        to.clear();
        if (length > 0) {
          final int startPoint = offsetBuffer.getInt((long) startIndex * OFFSET_WIDTH);
          // we have to scan by index since there are out-of-order offsets
          to.offsetBuffer = to.allocateBuffers((long) length * OFFSET_WIDTH);
          to.sizeBuffer = to.allocateBuffers((long) length * SIZE_WIDTH);
  
          /* splitAndTransfer the size buffer */
          int maxOffsetAndSizeSum = -1;
          int minOffsetValue = -1;
          for (int i = 0; i < length; i++) {
            final int offsetValue = offsetBuffer.getInt((long) (startIndex + i) * OFFSET_WIDTH);
            final int sizeValue = sizeBuffer.getInt((long) (startIndex + i) * SIZE_WIDTH);
            to.sizeBuffer.setInt((long) i * SIZE_WIDTH, sizeValue);
            if (maxOffsetAndSizeSum < offsetValue + sizeValue) {
              maxOffsetAndSizeSum = offsetValue + sizeValue;
            }
            if (minOffsetValue == -1 || minOffsetValue > offsetValue) {
              minOffsetValue = offsetValue;
            }
          }
  
          /* splitAndTransfer the offset buffer */
          for (int i = 0; i < length; i++) {
            final int offsetValue = offsetBuffer.getInt((long) (startIndex + i) * OFFSET_WIDTH);
            final int relativeOffset = offsetValue - minOffsetValue;
            to.offsetBuffer.setInt((long) i * OFFSET_WIDTH, relativeOffset);
          }
  
          /* splitAndTransfer the validity buffer */
          splitAndTransferValidityBuffer(startIndex, length, to);
  
          /* splitAndTransfer the data buffer */
          final int childSliceLength = maxOffsetAndSizeSum - minOffsetValue;
          dataTransferPair.splitAndTransfer(minOffsetValue, childSliceLength);
          to.setValueCount(length);
        }
      }
  
      @Override
      public ValueVector getTo() {
        return to;
      }
  
      @Override
      public void copyValueSafe(int from, int to) {
        this.to.copyFrom(from, to, ListViewVector.this);
      }
    }
  
    @Override
    protected FieldReader getReaderImpl() {
      return new UnionListViewReader(this);
    }
  
    @Override
    public UnionListViewReader getReader() {
      reader = (UnionListViewReader) super.getReader();
      return reader;
    }
  
    /**
     * Get the size (number of bytes) of underlying buffers used by this vector.
     *
     * @return size of underlying buffers.
     */
    @Override
    public int getBufferSize() {
      if (valueCount == 0) {
        return 0;
      }
      final int offsetBufferSize = valueCount * OFFSET_WIDTH;
      final int sizeBufferSize = valueCount * SIZE_WIDTH;
      final int validityBufferSize = BitVectorHelper.getValidityBufferSizeFromCount(valueCount);
      return offsetBufferSize + sizeBufferSize + validityBufferSize + vector.getBufferSize();
    }
  
    /**
     * Get the size (number of bytes) of underlying buffers used by this.
     *
     * @param valueCount the number of values to assume this vector contains
     * @return size of underlying buffers.
     */
    @Override
    public int getBufferSizeFor(int valueCount) {
      if (valueCount == 0) {
        return 0;
      }
      final int validityBufferSize = BitVectorHelper.getValidityBufferSizeFromCount(valueCount);
  
      return super.getBufferSizeFor(valueCount) + validityBufferSize;
    }
  
    /**
     * Get the field associated with the list view vector.
     *
     * @return the field
     */
    @Override
    public Field getField() {
      if (field.getChildren().contains(getDataVector().getField())) {
        return field;
      }
      field =
          new Field(
              field.getName(),
              field.getFieldType(),
              Collections.singletonList(getDataVector().getField()));
      return field;
    }
  
    /**
     * Get the minor type for the vector.
     *
     * @return the minor type
     */
    @Override
    public MinorType getMinorType() {
      return MinorType.LISTVIEW;
    }
  
    /** Clear the vector data. */
    @Override
    public void clear() {
      // calling superclass clear method which is releasing the sizeBufer and offsetBuffer
      super.clear();
      validityBuffer = releaseBuffer(validityBuffer);
    }
  
    /** Release the buffers associated with this vector. */
    @Override
    public void reset() {
      super.reset();
      validityBuffer.setZero(0, validityBuffer.capacity());
    }
  
    /**
     * Return the underlying buffers associated with this vector. Note that this doesn't impact the
     * reference counts for this buffer, so it only should be used for in-context access. Also note
     * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
     * (unless they change it).
     *
     * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
     *     the returned array will be the only reference to them. Also, this won't clear the child
     *     buffers.
     * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
     */
    @Override
    public ArrowBuf[] getBuffers(boolean clear) {
      setReaderAndWriterIndex();
      final ArrowBuf[] buffers;
      if (getBufferSize() == 0) {
        buffers = new ArrowBuf[0];
      } else {
        List<ArrowBuf> list = new ArrayList<>();
        // the order must be validity, offset and size buffers
        list.add(validityBuffer);
        list.add(offsetBuffer);
        list.add(sizeBuffer);
        list.addAll(Arrays.asList(vector.getBuffers(false)));
        buffers = list.toArray(new ArrowBuf[list.size()]);
      }
      if (clear) {
        for (ArrowBuf buffer : buffers) {
          buffer.getReferenceManager().retain();
        }
        clear();
      }
      return buffers;
    }
  
    /**
     * Get the element in the list view vector at a particular index.
     *
     * @param index position of the element
     * @return Object at given position
     */
    @Override
    public List<?> getObject(int index) {
      if (isSet(index) == 0) {
        return null;
      }
      final int start = offsetBuffer.getInt(index * OFFSET_WIDTH);
      final int end = start + sizeBuffer.getInt((index) * SIZE_WIDTH);
      final ValueVector vv = getDataVector();
      final List<Object> vals = new JsonStringArrayList<>(end - start);
      for (int i = start; i < end; i++) {
        vals.add(vv.getObject(i));
      }
  
      return vals;
    }
  
    /**
     * Check if an element at given index is null.
     *
     * @param index position of an element
     * @return true if an element at given index is null, false otherwise
     */
    @Override
    public boolean isNull(int index) {
      return (isSet(index) == 0);
    }
  
    /**
     * Check if an element at given index is an empty list.
     *
     * @param index position of an element
     * @return true if an element at given index is an empty list or NULL, false otherwise
     */
    @Override
    public boolean isEmpty(int index) {
      if (isNull(index)) {
        return true;
      } else {
        return sizeBuffer.getInt(index * SIZE_WIDTH) == 0;
      }
    }
  
    /**
     * Same as {@link #isNull(int)}.
     *
     * @param index position of the element
     * @return 1 if element at given index is not null, 0 otherwise
     */
    public int isSet(int index) {
      final int byteIndex = index >> 3;
      final byte b = validityBuffer.getByte(byteIndex);
      final int bitIndex = index & 7;
      return (b >> bitIndex) & 0x01;
    }
  
    /**
     * Get the number of elements that are null in the vector.
     *
     * @return the number of null elements.
     */
    @Override
    public int getNullCount() {
      return BitVectorHelper.getNullCount(validityBuffer, valueCount);
    }
  
    /**
     * Get the value capacity by considering validity and offset capacity. Note that the size buffer
     * capacity is not considered here since it has the same capacity as the offset buffer.
     *
     * @return the value capacity
     */
    @Override
    public int getValueCapacity() {
      return getValidityAndOffsetValueCapacity();
    }
  
    private int getValidityAndSizeValueCapacity() {
      final int offsetValueCapacity = Math.max(getOffsetBufferValueCapacity(), 0);
      final int sizeValueCapacity = Math.max(getSizeBufferValueCapacity(), 0);
      return Math.min(offsetValueCapacity, sizeValueCapacity);
    }
  
    private int getValidityAndOffsetValueCapacity() {
      final int offsetValueCapacity = Math.max(getOffsetBufferValueCapacity(), 0);
      return Math.min(offsetValueCapacity, getValidityBufferValueCapacity());
    }
  
    private int getValidityBufferValueCapacity() {
      return capAtMaxInt(validityBuffer.capacity() * 8);
    }
  
    /**
     * Set the element at the given index to null.
     *
     * @param index the value to change
     */
    @Override
    public void setNull(int index) {
      while (index >= getValidityAndSizeValueCapacity()) {
        reallocValidityAndSizeAndOffsetBuffers();
      }
  
      offsetBuffer.setInt(index * OFFSET_WIDTH, 0);
      sizeBuffer.setInt(index * SIZE_WIDTH, 0);
      BitVectorHelper.unsetBit(validityBuffer, index);
    }
  
    /**
     * Start new value in the ListView vector.
     *
     * @param index index of the value to start
     * @return offset of the new value
     */
    @Override
    public int startNewValue(int index) {
      while (index >= getValidityAndSizeValueCapacity()) {
        reallocValidityAndSizeAndOffsetBuffers();
      }
  
      if (index > 0) {
        final int prevOffset = getMaxViewEndChildVectorByIndex(index);
        offsetBuffer.setInt(index * OFFSET_WIDTH, prevOffset);
      }
  
      BitVectorHelper.setBit(validityBuffer, index);
      return offsetBuffer.getInt(index * OFFSET_WIDTH);
    }
  
    /**
     * Validate the invariants of the offset and size buffers. 0 <= offsets[i] <= length of the child
     * array 0 <= offsets[i] + size[i] <= length of the child array
     *
     * @param offset the offset at a given index
     * @param size the size at a given index
     */
    private void validateInvariants(int offset, int size) {
      if (offset < 0) {
        throw new IllegalArgumentException("Offset cannot be negative");
      }
  
      if (size < 0) {
        throw new IllegalArgumentException("Size cannot be negative");
      }
  
      // 0 <= offsets[i] <= length of the child array
      if (offset > this.vector.getValueCount()) {
        throw new IllegalArgumentException("Offset is out of bounds.");
      }
  
      // 0 <= offsets[i] + size[i] <= length of the child array
      if (offset + size > this.vector.getValueCount()) {
        throw new IllegalArgumentException("Offset + size <= length of the child array.");
      }
    }
  
    /**
     * Set the offset at the given index. Make sure to use this function after updating `field` vector
     * and using `setValidity`
     *
     * @param index index of the value to set
     * @param value value to set
     */
    public void setOffset(int index, int value) {
      validateInvariants(value, sizeBuffer.getInt(index * SIZE_WIDTH));
  
      offsetBuffer.setInt(index * OFFSET_WIDTH, value);
    }
  
    /**
     * Set the size at the given index. Make sure to use this function after using `setOffset`.
     *
     * @param index index of the value to set
     * @param value value to set
     */
    public void setSize(int index, int value) {
      validateInvariants(offsetBuffer.getInt(index * SIZE_WIDTH), value);
  
      sizeBuffer.setInt(index * SIZE_WIDTH, value);
    }
  
    /**
     * Set the validity at the given index.
     *
     * @param index index of the value to set
     * @param value value to set (0 for unset and 1 for a set)
     */
    public void setValidity(int index, int value) {
      if (value == 0) {
        BitVectorHelper.unsetBit(validityBuffer, index);
      } else {
        BitVectorHelper.setBit(validityBuffer, index);
      }
    }
  
    @Override
    public void setValueCount(int valueCount) {
      this.valueCount = valueCount;
      if (valueCount > 0) {
        while (valueCount > getValidityAndSizeValueCapacity()) {
          /* check if validity and offset buffers need to be re-allocated */
          reallocValidityAndSizeAndOffsetBuffers();
        }
      }
      /* valueCount for the data vector is the current end offset */
      final int childValueCount = (valueCount == 0) ? 0 : getMaxViewEndChildVector();
      /* set the value count of data vector and this will take care of
       * checking whether data buffer needs to be reallocated.
       */
      vector.setValueCount(childValueCount);
    }
  
    @Override
    public int getElementStartIndex(int index) {
      return offsetBuffer.getInt(index * OFFSET_WIDTH);
    }
  
    @Override
    public int getElementEndIndex(int index) {
      return sizeBuffer.getInt(index * OFFSET_WIDTH);
    }
  
    @Override
    public <T extends ValueVector> AddOrGetResult<T> addOrGetVector(FieldType fieldType) {
      AddOrGetResult<T> result = super.addOrGetVector(fieldType);
      invalidateReader();
      return result;
    }
  
    @Override
    public UnionVector promoteToUnion() {
      UnionVector vector = new UnionVector("$data$", allocator, /* field type*/ null, callBack);
      replaceDataVector(vector);
      invalidateReader();
      if (callBack != null) {
        callBack.doWork();
      }
      return vector;
    }
  
    private void invalidateReader() {
      reader = null;
    }
  
    @Deprecated
    @Override
    public List<BufferBacked> getFieldInnerVectors() {
      throw new UnsupportedOperationException("There are no inner vectors. Use getFieldBuffers");
    }
  
    public UnionListViewWriter getWriter() {
      return new UnionListViewWriter(this);
    }
  
    @Override
    public int getValueCount() {
      return valueCount;
    }
  
    /**
     * Get the density of this ListVector.
     *
     * @return density
     */
    public double getDensity() {
      if (valueCount == 0) {
        return 0.0D;
      }
      final double totalListSize = getMaxViewEndChildVector();
      return totalListSize / valueCount;
    }
  
    /** Validating ListViewVector creation based on the specification guideline. */
    @Override
    public void validate() {
      for (int i = 0; i < valueCount; i++) {
        final int offset = offsetBuffer.getInt(i * OFFSET_WIDTH);
        final int size = sizeBuffer.getInt(i * SIZE_WIDTH);
        validateInvariants(offset, size);
      }
    }
  
    /**
     * End the current value.
     *
     * @param index index of the value to end
     * @param size number of elements in the list that was written
     */
    public void endValue(int index, int size) {
      sizeBuffer.setInt(index * SIZE_WIDTH, size);
    }
  }
  