[FLINK-12983][metrics] replace descriptive histogram's storage back-end

Instead of using `DescriptiveStatistics` and its `ResizableDoubleArray` storage
back-end, implement an own circular array based on a fixed-size double array
that wraps around. This significantly improves the time needed to add new
values. It also ensures that access is synchronized which `ResizableDoubleArray`
does not guarantee.

flink-runtime/src/main/java/org/apache/flink/runtime/metrics/DescriptiveStatisticsHistogram.java

@@ -27,27 +27,63 @@
  */
 public class DescriptiveStatisticsHistogram implements org.apache.flink.metrics.Histogram {
 
- private final DescriptiveStatistics descriptiveStatistics;
-
- private long elementsSeen = 0L;
+ private final CircularDoubleArray descriptiveStatistics;
 
  public DescriptiveStatisticsHistogram(int windowSize) {
- this.descriptiveStatistics = new DescriptiveStatistics(windowSize);
+ this.descriptiveStatistics = new CircularDoubleArray(windowSize);
  }
 
  @Override
  public void update(long value) {
- elementsSeen += 1L;
  this.descriptiveStatistics.addValue(value);
  }
 
  @Override
  public long getCount() {
- return this.elementsSeen;
+ return this.descriptiveStatistics.getElementsSeen();
  }
 
  @Override
  public HistogramStatistics getStatistics() {
  return new DescriptiveStatisticsHistogramStatistics(this.descriptiveStatistics);
  }
+
+ /**
+ * Fixed-size array that wraps around at the end and has a dynamic start position.
+ */
+ static class CircularDoubleArray {
+ private final double[] backingArray;
+ private int nextPos = 0;
+ private boolean fullSize = false;
+ private long elementsSeen = 0;
+
+ CircularDoubleArray(int windowSize) {
+ this.backingArray = new double[windowSize];
+ }
+
+ synchronized void addValue(double value) {
+ backingArray[nextPos] = value;
+ ++elementsSeen;
+ ++nextPos;
+ if (nextPos == backingArray.length) {
+ nextPos = 0;
+ fullSize = true;
+ }
+ }
+
+ synchronized double[] toUnsortedArray() {
+ final int size = getSize();
+ double[] result = new double[size];
+ System.arraycopy(backingArray, 0, result, 0, result.length);
+ return result;
+ }
+
+ private synchronized int getSize() {
+ return fullSize ? backingArray.length : nextPos;
+ }
+
+ private synchronized long getElementsSeen() {
+ return elementsSeen;
+ }
+ }
 }

flink-runtime/src/main/java/org/apache/flink/runtime/metrics/DescriptiveStatisticsHistogramStatistics.java

@@ -38,8 +38,9 @@
 public class DescriptiveStatisticsHistogramStatistics extends HistogramStatistics {
  private final CommonMetricsSnapshot statisticsSummary = new CommonMetricsSnapshot();
 
- public DescriptiveStatisticsHistogramStatistics(DescriptiveStatistics latencyHistogram) {
- latencyHistogram.apply(statisticsSummary);
+ public DescriptiveStatisticsHistogramStatistics(
+ DescriptiveStatisticsHistogram.CircularDoubleArray histogramValues) {
+ statisticsSummary.evaluate(histogramValues.toUnsortedArray());
  }
 
  @Override