histogram_aggregator.hpp

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#pragma once
 
/// @file userver/utils/statistics/histogram_aggregator.hpp
/// @brief @copybrief utils::statistics::HistogramAggregator
 
#include <memory>
 
#include <userver/utils/span.hpp>
#include <userver/utils/statistics/fwd.hpp>
#include <userver/utils/statistics/histogram_view.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils::statistics {
 
/// @brief Used to aggregate multiple utils::statistics::Histogram metrics.
///
/// Usage example:
/// @snippet utils/statistics/histogram_test.cpp  HistogramAggregator
class HistogramAggregator final {
public:
    /// @brief Sets upper bounds for each non-"infinite" bucket. The lowest bound is
    /// always 0.
    ///
    /// @param upper_bounds is copied inside and is not required to be kept alive after the constructor completes.
    explicit HistogramAggregator(utils::span<const double> upper_bounds);
 
    HistogramAggregator(HistogramAggregator&&) noexcept;
    HistogramAggregator& operator=(HistogramAggregator&&) noexcept;
    ~HistogramAggregator();
 
    /// @brief Add the other histogram to the current one.
    ///
    /// Bucket borders in `this` and `other` must be either identical, or bucket
    /// borders in `this` must be a strict subset of bucket borders in `other`.
    ///
    /// Writes to `*this` are non-atomic.
    void Add(HistogramView other);
 
    /// Non-atomically increment the bucket corresponding to the given index.
    void AccountAt(std::size_t bucket_index, std::uint64_t count = 1) noexcept;
 
    /// Non-atomically increment the "infinity" bucket.
    void AccountInf(std::uint64_t count = 1) noexcept;
 
    /// Reset all buckets to zero.
    void Reset() noexcept;
 
    /// Allows reading the histogram.
    HistogramView GetView() const& noexcept;
 
    /// @cond
    // Store Histogram in a variable before taking a view on it.
    HistogramView GetView() && noexcept = delete;
    /// @endcond
 
private:
    std::unique_ptr<impl::histogram::Bucket[]> buckets_;
};
 
/// Metric serialization support for HistogramAggregator.
void DumpMetric(Writer& writer, const HistogramAggregator& histogram);
 
}  // namespace utils::statistics
 
USERVER_NAMESPACE_END