+ return ss.str();
+}
+
+void Histogram::init(const vector<double> &bucket_vals)
+{
+ this->num_buckets = bucket_vals.size();
+ buckets.reset(new Bucket[num_buckets]);
+ for (size_t i = 0; i < num_buckets; ++i) {
+ buckets[i].val = bucket_vals[i];
+ }
+}
+
+void Histogram::init_uniform(size_t num_buckets)
+{
+ this->num_buckets = num_buckets;
+ buckets.reset(new Bucket[num_buckets]);
+ for (size_t i = 0; i < num_buckets; ++i) {
+ buckets[i].val = i;
+ }
+}
+
+void Histogram::init_geometric(double min, double max, size_t num_buckets)
+{
+ this->num_buckets = num_buckets;
+ buckets.reset(new Bucket[num_buckets]);
+ for (size_t i = 0; i < num_buckets; ++i) {
+ buckets[i].val = min * pow(max / min, double(i) / (num_buckets - 1));
+ }
+}
+
+void Histogram::count_event(double val)
+{
+ Bucket ref_bucket;
+ ref_bucket.val = val;
+ auto it = lower_bound(buckets.get(), buckets.get() + num_buckets, ref_bucket,
+ [](const Bucket &a, const Bucket &b) { return a.val < b.val; });
+ if (it == buckets.get() + num_buckets) {
+ ++count_after_last_bucket;
+ } else {
+ ++it->count;
+ }
+ // Non-atomic add, but that's fine, since there are no concurrent writers.
+ sum = sum + val;
+}
+
+string Histogram::serialize(Metrics::Laziness laziness, const string &name, const vector<pair<string, string>> &labels) const
+{
+ // Check if the histogram is empty and should not be serialized.
+ if (laziness == Metrics::PRINT_WHEN_NONEMPTY && count_after_last_bucket.load() == 0) {
+ bool empty = true;
+ for (size_t bucket_idx = 0; bucket_idx < num_buckets; ++bucket_idx) {
+ if (buckets[bucket_idx].count.load() != 0) {
+ empty = false;
+ break;
+ }
+ }
+ if (empty) {
+ return "";
+ }
+ }
+
+ stringstream ss;
+ ss.imbue(locale("C"));
+ ss.precision(20);
+
+ int64_t count = 0;
+ for (size_t bucket_idx = 0; bucket_idx < num_buckets; ++bucket_idx) {
+ stringstream le_ss;
+ le_ss.imbue(locale("C"));
+ le_ss.precision(20);
+ le_ss << buckets[bucket_idx].val;
+ vector<pair<string, string>> bucket_labels = labels;
+ bucket_labels.emplace_back("le", le_ss.str());
+
+ count += buckets[bucket_idx].count.load();
+ ss << Metrics::serialize_name(name + "_bucket", bucket_labels) << " " << count << "\n";
+ }
+
+ count += count_after_last_bucket.load();
+
+ ss << Metrics::serialize_name(name + "_sum", labels) << " " << sum.load() << "\n";
+ ss << Metrics::serialize_name(name + "_count", labels) << " " << count << "\n";
+
+ return ss.str();
+}
+
+void Summary::init(const vector<double> &quantiles, double window_seconds)
+{
+ this->quantiles = quantiles;
+ window = duration<double>(window_seconds);
+}
+
+void Summary::count_event(double val)
+{
+ steady_clock::time_point now = steady_clock::now();
+ steady_clock::time_point cutoff = now - duration_cast<steady_clock::duration>(window);
+
+ lock_guard<mutex> lock(mu);
+ values.emplace_back(now, val);
+ while (!values.empty() && values.front().first < cutoff) {
+ values.pop_front();
+ }
+
+ // Non-atomic add, but that's fine, since there are no concurrent writers.
+ sum = sum + val;
+ ++count;
+}
+
+string Summary::serialize(Metrics::Laziness laziness, const string &name, const vector<pair<string, string>> &labels)
+{
+ steady_clock::time_point now = steady_clock::now();
+ steady_clock::time_point cutoff = now - duration_cast<steady_clock::duration>(window);
+
+ vector<double> values_copy;
+ {
+ lock_guard<mutex> lock(mu);
+ while (!values.empty() && values.front().first < cutoff) {
+ values.pop_front();
+ }
+ values_copy.reserve(values.size());
+ for (const auto &time_and_value : values) {
+ values_copy.push_back(time_and_value.second);
+ }
+ }
+
+ vector<pair<double, double>> answers;
+ if (values_copy.size() == 0) {
+ if (laziness == Metrics::PRINT_WHEN_NONEMPTY) {
+ return "";
+ }
+ for (double quantile : quantiles) {
+ answers.emplace_back(quantile, 0.0 / 0.0);
+ }
+ } else if (values_copy.size() == 1) {
+ for (double quantile : quantiles) {
+ answers.emplace_back(quantile, values_copy[0]);
+ }
+ } else {
+ // We could probably do repeated nth_element, but the constant factor
+ // gets a bit high, so just sorting probably is about as fast.
+ sort(values_copy.begin(), values_copy.end());
+ for (double quantile : quantiles) {
+ double idx = quantile * (values_copy.size() - 1);
+ size_t idx_floor = size_t(floor(idx));
+ const double v0 = values_copy[idx_floor];
+
+ if (idx_floor == values_copy.size() - 1) {
+ answers.emplace_back(quantile, values_copy[idx_floor]);
+ } else {
+ // Linear interpolation.
+ double t = idx - idx_floor;
+ const double v1 = values_copy[idx_floor + 1];
+ answers.emplace_back(quantile, v0 + t * (v1 - v0));
+ }
+ }
+ }
+
+ stringstream ss;
+ ss.imbue(locale("C"));
+ ss.precision(20);
+
+ for (const auto &quantile_and_value : answers) {
+ stringstream quantile_ss;
+ quantile_ss.imbue(locale("C"));
+ quantile_ss.precision(3);
+ quantile_ss << quantile_and_value.first;
+ vector<pair<string, string>> quantile_labels = labels;
+ quantile_labels.emplace_back("quantile", quantile_ss.str());
+
+ double val = quantile_and_value.second;;
+ if (isnan(val)) {
+ // Prometheus can't handle “-nan”.
+ ss << Metrics::serialize_name(name, quantile_labels) << " NaN\n";
+ } else {
+ ss << Metrics::serialize_name(name, quantile_labels) << " " << val << "\n";