src/test/java/org/apache/datasketches/quantiles/ClassicQuantilesMemorySegmentRequestApp.java

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 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
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 *
 *   http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.datasketches.quantiles;

import static org.testng.Assert.assertEquals;
import static org.testng.Assert.assertTrue;

import java.lang.foreign.MemorySegment;

import org.apache.datasketches.common.MemorySegmentRequestExample;
import org.testng.annotations.Test;

public class ClassicQuantilesMemorySegmentRequestApp {

  @Test
  /**
   * This method emulates an application using an off-heap QuantilesDoublesSketch that needs to expand off-heap.
   * This demonstrates one example of how to manage a growing off-heap QuantilesDoublesSketch where the
   * expanded MemorySegments are also off-heap.
   */
  public void checkMemorySegmentRequestExample() {
    final int k = 128; //The default is 128
    final int itemsIn = 40 * k; //will force requests for more space

    //Use the custom MemorySegmentRequestExample to do the allocations.
    final MemorySegmentRequestExample mSegReqEx = new MemorySegmentRequestExample();

    //The allocation of the original off-heap MemorySegment for the QuantilesDoublesSketch
    //Note that this targets the size to only handle 2k values, which is quite small.
    final int initalBytes = QuantilesDoublesSketch.getUpdatableStorageBytes(k, 2 * k);

    final MemorySegment seg = mSegReqEx.request(initalBytes);

    //Create a new KllLongsSketch and pass the mSegReqEx
    final QuantilesDoublesSketch sk = QuantilesDoublesSketch.builder().setK(k).build(seg, mSegReqEx);

    //Update the sketch with way more data than the original MemorySegment can handle, forcing it to request larger MemorySegments.
    for (int n = 1; n <= itemsIn; n++) { sk.update(n); }

    //Check to make sure the sketch got all the data:
    assertEquals(sk.getMaxItem(), itemsIn);
    assertEquals(sk.getMinItem(), 1);
    assertEquals(sk.getN(), itemsIn);

    //Confirm that the last MemorySegment used by the sketch is, in fact, not the same as the original one that was allocated.
    assertTrue(sk.getMemorySegment() != seg);

    //All done with the sketch. Cleanup any unclosed off-heap MemorySegments.
    mSegReqEx.cleanup();
  }

}