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/*
*
* Copyright 2015 gRPC authors.
*
* 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.
*
*/
#include <grpc/support/histogram.h>
#include <math.h>
#include <stddef.h>
#include <string.h>
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/port_platform.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 */
uint32_t* 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, 1.0, h->max_possible));
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_histogram*)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 = (uint32_t*)gpr_zalloc(sizeof(uint32_t) * 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, const gpr_histogram* src) {
if ((dst->num_buckets != src->num_buckets) ||
(dst->multiplier != src->multiplier)) {
/* Fail because these histograms don't match */
return 0;
}
gpr_histogram_merge_contents(dst, src->buckets, src->num_buckets,
src->min_seen, src->max_seen, src->sum,
src->sum_of_squares, src->count);
return 1;
}
void gpr_histogram_merge_contents(gpr_histogram* dst, const uint32_t* data,
size_t data_count, double min_seen,
double max_seen, double sum,
double sum_of_squares, double count) {
size_t i;
GPR_ASSERT(dst->num_buckets == data_count);
dst->sum += sum;
dst->sum_of_squares += sum_of_squares;
dst->count += count;
if (min_seen < dst->min_seen) {
dst->min_seen = min_seen;
}
if (max_seen > dst->max_seen) {
dst->max_seen = max_seen;
}
for (i = 0; i < dst->num_buckets; i++) {
dst->buckets[i] += data[i];
}
}
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;
if (h->count == 0) {
return 0.0;
}
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, (double)lower_idx) +
bucket_start(h, (double)upper_idx)) /
2.0;
} else {
/* treat values as uniform throughout the bucket, and find where this value
should lie */
lower_bound = bucket_start(h, (double)lower_idx);
upper_bound = bucket_start(h, (double)(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 != 0);
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;
}
const uint32_t* gpr_histogram_get_contents(gpr_histogram* h, size_t* size) {
*size = h->num_buckets;
return h->buckets;
}
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