1 files changed, 226 insertions, 0 deletions
diff --git a/src/core/support/histogram.c b/src/core/support/histogram.c
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+/*
+ *
+ * Copyright 2014, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <grpc/support/histogram.h>
+
+#include <math.h>
+#include <stddef.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/port_platform.h>
+#include <grpc/support/log.h>
+#include <grpc/support/useful.h>
+
+/* Histograms are stored with exponentially increasing bucket sizes.
+   The first bucket is [0, m) where m = 1 + resolution
+   Bucket n (n>=1) contains [m**n, m**(n+1))
+   There are sufficient buckets to reach max_bucket_start */
+
+struct gpr_histogram {
+  /* Sum of all values seen so far */
+  double sum;
+  /* Sum of squares of all values seen so far */
+  double sum_of_squares;
+  /* number of values seen so far */
+  double count;
+  /* m in the description */
+  double multiplier;
+  double one_on_log_multiplier;
+  /* minimum value seen */
+  double min_seen;
+  /* maximum value seen */
+  double max_seen;
+  /* maximum representable value */
+  double max_possible;
+  /* number of buckets */
+  size_t num_buckets;
+  /* the buckets themselves */
+  gpr_uint32 *buckets;
+};
+
+/* determine a bucket index given a value - does no bounds checking */
+static size_t bucket_for_unchecked(gpr_histogram *h, double x) {
+  return (size_t)(log(x) * h->one_on_log_multiplier);
+}
+
+/* bounds checked version of the above */
+static size_t bucket_for(gpr_histogram *h, double x) {
+  size_t bucket = bucket_for_unchecked(h, GPR_CLAMP(x, 0, h->max_possible));
+  GPR_ASSERT(bucket >= 0);
+  GPR_ASSERT(bucket < h->num_buckets);
+  return bucket;
+}
+
+/* at what value does a bucket start? */
+static double bucket_start(gpr_histogram *h, double x) {
+  return pow(h->multiplier, x);
+}
+
+gpr_histogram *gpr_histogram_create(double resolution,
+                                    double max_bucket_start) {
+  gpr_histogram *h = gpr_malloc(sizeof(gpr_histogram));
+  GPR_ASSERT(resolution > 0.0);
+  GPR_ASSERT(max_bucket_start > resolution);
+  h->sum = 0.0;
+  h->sum_of_squares = 0.0;
+  h->multiplier = 1.0 + resolution;
+  h->one_on_log_multiplier = 1.0 / log(1.0 + resolution);
+  h->max_possible = max_bucket_start;
+  h->count = 0.0;
+  h->min_seen = max_bucket_start;
+  h->max_seen = 0.0;
+  h->num_buckets = bucket_for_unchecked(h, max_bucket_start) + 1;
+  GPR_ASSERT(h->num_buckets > 1);
+  GPR_ASSERT(h->num_buckets < 100000000);
+  h->buckets = gpr_malloc(sizeof(gpr_uint32) * h->num_buckets);
+  memset(h->buckets, 0, sizeof(gpr_uint32) * h->num_buckets);
+  return h;
+}
+
+void gpr_histogram_destroy(gpr_histogram *h) {
+  gpr_free(h->buckets);
+  gpr_free(h);
+}
+
+void gpr_histogram_add(gpr_histogram *h, double x) {
+  h->sum += x;
+  h->sum_of_squares += x * x;
+  h->count++;
+  if (x < h->min_seen) {
+    h->min_seen = x;
+  }
+  if (x > h->max_seen) {
+    h->max_seen = x;
+  }
+  h->buckets[bucket_for(h, x)]++;
+}
+
+int gpr_histogram_merge(gpr_histogram *dst, gpr_histogram *src) {
+  int i;
+  if ((dst->num_buckets != src->num_buckets) ||
+      (dst->multiplier != src->multiplier)) {
+    /* Fail because these histograms don't match */
+    return 0;
+  }
+  dst->sum += src->sum;
+  dst->sum_of_squares += src->sum_of_squares;
+  dst->count += src->count;
+  if (src->min_seen < dst->min_seen) {
+    dst->min_seen = src->min_seen;
+  }
+  if (src->max_seen > dst->max_seen) {
+    dst->max_seen = src->max_seen;
+  }
+  for (i = 0; i < dst->num_buckets; i++) {
+    dst->buckets[i] += src->buckets[i];
+  }
+  return 1;
+}
+
+static double threshold_for_count_below(gpr_histogram *h, double count_below) {
+  double count_so_far;
+  double lower_bound;
+  double upper_bound;
+  int lower_idx;
+  int upper_idx;
+
+  GPR_ASSERT(h->count >= 1);
+
+  if (count_below <= 0) {
+    return h->min_seen;
+  }
+  if (count_below >= h->count) {
+    return h->max_seen;
+  }
+
+  /* find the lowest bucket that gets us above count_below */
+  count_so_far = 0.0;
+  for (lower_idx = 0; lower_idx < h->num_buckets; lower_idx++) {
+    count_so_far += h->buckets[lower_idx];
+    if (count_so_far >= count_below) {
+      break;
+    }
+  }
+  if (count_so_far == count_below) {
+    /* this bucket hits the threshold exactly... we should be midway through
+       any run of zero values following the bucket */
+    for (upper_idx = lower_idx + 1; upper_idx < h->num_buckets; upper_idx++) {
+      if (h->buckets[upper_idx]) {
+        break;
+      }
+    }
+    return (bucket_start(h, lower_idx) + bucket_start(h, upper_idx)) / 2.0;
+  } else {
+    /* treat values as uniform throughout the bucket, and find where this value
+       should lie */
+    lower_bound = bucket_start(h, lower_idx);
+    upper_bound = bucket_start(h, lower_idx + 1);
+    return GPR_CLAMP(upper_bound -
+                         (upper_bound - lower_bound) *
+                             (count_so_far - count_below) /
+                             h->buckets[lower_idx],
+                     h->min_seen, h->max_seen);
+  }
+}
+
+double gpr_histogram_percentile(gpr_histogram *h, double percentile) {
+  return threshold_for_count_below(h, h->count * percentile / 100.0);
+}
+
+double gpr_histogram_mean(gpr_histogram *h) {
+  GPR_ASSERT(h->count);
+  return h->sum / h->count;
+}
+
+double gpr_histogram_stddev(gpr_histogram *h) {
+  return sqrt(gpr_histogram_variance(h));
+}
+
+double gpr_histogram_variance(gpr_histogram *h) {
+  if (h->count == 0) return 0.0;
+  return (h->sum_of_squares * h->count - h->sum * h->sum) /
+         (h->count * h->count);
+}
+
+double gpr_histogram_maximum(gpr_histogram *h) { return h->max_seen; }
+
+double gpr_histogram_minimum(gpr_histogram *h) { return h->min_seen; }
+
+double gpr_histogram_count(gpr_histogram *h) { return h->count; }
+
+double gpr_histogram_sum(gpr_histogram *h) { return h->sum; }
+
+double gpr_histogram_sum_of_squares(gpr_histogram *h) {
+  return h->sum_of_squares;
+}