Add new class to create cpu usage time series.

RELNOTES: None
PiperOrigin-RevId: 208462186

1 files changed, 87 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/profiler/CpuUsageTimeSeries.java b/src/main/java/com/google/devtools/build/lib/profiler/CpuUsageTimeSeries.java
new file mode 100644
index 0000000000..faadb7357a
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/profiler/CpuUsageTimeSeries.java
@@ -0,0 +1,87 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// 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 com.google.devtools.build.lib.profiler;
+
+import java.util.Arrays;
+
+/**
+ * Converts a set of ranges into a graph by counting the number of ranges that are active at any
+ * point in time. Time is split into equal-sized buckets, and we compute one value per bucket. If a
+ * range partially overlaps a bucket, then the bucket is incremented by the fraction of overlap.
+ */
+public class CpuUsageTimeSeries {
+  private final long startTimeMillis;
+  private final long bucketSizeMillis;
+  private static final int INITIAL_SIZE = 100;
+  private double[] data = new double[INITIAL_SIZE];
+
+  public CpuUsageTimeSeries(long startTimeMillis, long bucketSizeMillis) {
+    this.startTimeMillis = startTimeMillis;
+    this.bucketSizeMillis = bucketSizeMillis;
+  }
+
+  public void addRange(long startTimeMillis, long endTimeMillis) {
+    addRange(startTimeMillis, endTimeMillis, /* value= */ 1);
+  }
+
+  /** Adds a new range to the time series, by increasing every affected bucket by value. */
+  public void addRange(long rangeStartMillis, long rangeEndMillis, double value) {
+    // Compute times relative to start and their positions in the data array.
+    rangeStartMillis -= startTimeMillis;
+    rangeEndMillis -= startTimeMillis;
+    int startPosition = (int) (rangeStartMillis / bucketSizeMillis);
+    int endPosition = (int) (rangeEndMillis / bucketSizeMillis);
+
+    // Assume we add the following range R:
+    // ----------------------------------
+    // |     |ssRRR|RRRRR|Reeee|      |
+    // ----------------------------------
+    // we cannot just add value to each affected bucket but have to correct the values for the first
+    // and last bucket by calculating the size of 's' and 'e'.
+    double missingStartFraction =
+        ((double) (rangeStartMillis - bucketSizeMillis * startPosition)) / bucketSizeMillis;
+    double missingEndFraction =
+        ((double) (bucketSizeMillis * (endPosition + 1) - rangeEndMillis)) / bucketSizeMillis;
+
+    if (startPosition < 0) {
+      startPosition = 0;
+      missingStartFraction = 0;
+    }
+    if (endPosition < startPosition) {
+      endPosition = startPosition;
+      missingEndFraction = 0;
+    }
+
+    // Resize data array if necessary so it can at least fit endPosition.
+    if (endPosition >= data.length) {
+      data = Arrays.copyOf(data, Math.max(endPosition + 1, 2 * data.length));
+    }
+
+    // Do the actual update.
+    for (int i = startPosition; i <= endPosition; i++) {
+      double fraction = 1;
+      if (i == startPosition) {
+        fraction -= missingStartFraction;
+      }
+      if (i == endPosition) {
+        fraction -= missingEndFraction;
+      }
+      data[i] += fraction * value;
+    }
+  }
+
+  public double[] toDoubleArray(int len) {
+    return Arrays.copyOf(data, len);
+  }
+}