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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) {
size_t 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;
size_t lower_idx;
size_t 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;
}
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