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This project provides java bindings for cudf, to be able to process large amounts of data on a GPU. This is still a work in progress so some APIs may change until the 1.0 release.

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/*
 *
 *  Copyright (c) 2023, NVIDIA CORPORATION.
 *
 *  Licensed 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 ai.rapids.cudf;

import java.nio.ByteBuffer;

/**
 * Metadata for a table that is backed by a single contiguous device buffer.
 */
public final class PackedColumnMetadata implements AutoCloseable {
  private long metadataHandle = 0;
  private ByteBuffer metadataBuffer = null;

  // This method is invoked by JNI
  static PackedColumnMetadata fromPackedColumnMeta(long metadataHandle) {
    return new PackedColumnMetadata(metadataHandle);
  }

  /**
   * Construct the PackedColumnMetadata instance given a metadata handle.
   * @param metadataHandle address of the cudf packed_table host-based metadata instance
   */
  PackedColumnMetadata(long metadataHandle) {
    this.metadataHandle = metadataHandle;
  }

  /**
   * Get the byte buffer containing the host metadata describing the schema and layout of the
   * contiguous table.
   * 
   * NOTE: This is a direct byte buffer that is backed by the underlying native metadata instance
   *       and therefore is only valid to be used while this PackedColumnMetadata instance is valid.
   *       Attempts to cache and access the resulting buffer after this instance has been destroyed
   *       will result in undefined behavior including the possibility of segmentation faults
   *       or data corruption.
   */
  public ByteBuffer getMetadataDirectBuffer() {
    if (metadataBuffer == null) {
      metadataBuffer = createMetadataDirectBuffer(metadataHandle);
    }
    return metadataBuffer.asReadOnlyBuffer();
  }

  /** Close the PackedColumnMetadata instance and its underlying resources. */
  @Override
  public void close() {
    if (metadataHandle != 0) {
      closeMetadata(metadataHandle);
      metadataHandle = 0;
    }
  }

  // create a DirectByteBuffer for the packed metadata
  private static native ByteBuffer createMetadataDirectBuffer(long metadataHandle);

  // release the native metadata resources for a packed table
  private static native void closeMetadata(long metadataHandle);
}