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+/**
+ * Copyright (C) 2021-present MongoDB, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the Server Side Public License, version 1,
+ * as published by MongoDB, Inc.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * Server Side Public License for more details.
+ *
+ * You should have received a copy of the Server Side Public License
+ * along with this program. If not, see
+ * <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the Server Side Public License in all respects for
+ * all of the code used other than as permitted herein. If you modify file(s)
+ * with this exception, you may extend this exception to your version of the
+ * file(s), but you are not obligated to do so. If you do not wish to do so,
+ * delete this exception statement from your version. If you delete this
+ * exception statement from all source files in the program, then also delete
+ * it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/db/commands.h"
+#include <vector>
+
+namespace mongo {
+
+/**
+ * Generalized version of OperationLatencyHistogram that can track latencies for any operation type
+ * with custom lower bounds. For some provided lower bounds {x,y} a number z will be counted in the
+ * x-y bucket if z ∈ [x, y). in the y-inf bucket if z ∈ [y, inf). and in the (-inf, x) bucket if z <
+ * x.
+ */
+template <std::size_t numLowerBounds>
+class IntegerHistogram {
+public:
+ const std::string kKey;
+
+ IntegerHistogram(std::string key, std::array<int64_t, numLowerBounds> lowerBounds)
+ : kKey(std::move(key)) {
+ invariant(!lowerBounds.empty(), "Lower bounds must not be empty");
+ _lowerBoundBuckets[0].lowerBound = std::numeric_limits<int64_t>::min();
+ int64_t prevVal = std::numeric_limits<int64_t>::min();
+ for (size_t i = 1; i < _lowerBoundBuckets.size(); ++i) {
+ auto lowerBoundVal = lowerBounds.at(i - 1);
+ invariant(lowerBoundVal > prevVal,
+ "Lower bounds must be strictly monotonically increasing");
+
+ _lowerBoundBuckets[i].lowerBound = lowerBoundVal;
+ prevVal = lowerBoundVal;
+ }
+ }
+
+ void append(BSONObjBuilder& builder, bool shouldAppendAdditionalInfo) const {
+ BSONObjBuilder histogramBuilder(builder.subobjStart(kKey));
+ auto offsetToString = [this](size_t offset) {
+ if (offset == 0)
+ return std::string("-inf");
+ if (offset < _lowerBoundBuckets.size())
+ return std::to_string(_lowerBoundBuckets[offset].lowerBound);
+ return std::string("inf");
+ };
+
+ for (size_t i = 0; i < _lowerBoundBuckets.size(); i++) {
+ auto count = _lowerBoundBuckets[i].count.load();
+ if (count == 0)
+ continue;
+
+ auto key = fmt::format("{} - {}", offsetToString(i), offsetToString(i + 1));
+ BSONObjBuilder entryBuilder(histogramBuilder.subobjStart(key));
+ entryBuilder.append("count", (long long)(count));
+ entryBuilder.doneFast();
+ }
+
+ auto totalCount = _entryCount.load();
+ histogramBuilder.append("ops", (long long)totalCount);
+ if (shouldAppendAdditionalInfo && totalCount != 0) {
+ auto sum = _sum.load();
+ histogramBuilder.append("sum", (long long)sum);
+ histogramBuilder.append("mean", static_cast<double>(sum) / totalCount);
+ }
+ histogramBuilder.doneFast();
+ }
+
+ void increment(int64_t data) {
+ auto insertionIndex = std::upper_bound(_lowerBoundBuckets.begin(),
+ _lowerBoundBuckets.end(),
+ data,
+ [](const int64_t a, const LowerBoundBucket& b) {
+ return a < b.lowerBound;
+ }) -
+ 1;
+
+ insertionIndex->count.addAndFetch(1);
+ _entryCount.addAndFetch(1);
+ _sum.addAndFetch(data);
+ }
+
+private:
+ struct LowerBoundBucket {
+ int64_t lowerBound;
+ AtomicWord<int64_t> count;
+ };
+
+ std::array<LowerBoundBucket, numLowerBounds + 1> _lowerBoundBuckets;
+ AtomicWord<int64_t> _entryCount;
+ AtomicWord<int64_t> _sum;
+};
+} // namespace mongo