metric_tag.hpp

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#pragma once
 
/// @file userver/utils/statistics/metric_tag.hpp
/// @brief @copybrief utils::statistics::MetricTag
 
#include <string>
#include <typeinfo>
#include <utility>
 
#include <userver/utils/statistics/metric_tag_impl.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils::statistics {
 
/// @brief Metric description and registration in a declarative way
///
/// Use `MetricTag<Metric>` for declarative style of metric registration and
/// call `MetricStorage::GetMetric` for accessing metric data. Please
/// note that metrics can be accessed from multiple coroutines, so `Metric` must
/// be thread-safe (e.g. std::atomic<T>, rcu::Variable<T>, rcu::RcuMap<T>,
/// concurrent::Variable<T>, etc.).
///
/// A custom metric type must be default-constructible and have the following
/// free function defined:
/// @code
/// void DumpMetric(utils::statistics::Writer&, const Metric&)
/// @endcode
///
/// For alerts consider using alerts::Source.
///
/// ## Example usage:
///
/// @snippet samples/tcp_full_duplex_service/main.cpp  TCP sample - Stats tag
/// where `Stats` are defined in a following way:
/// @snippet samples/tcp_full_duplex_service/main.cpp  TCP sample - Stats definition
///
/// For a full usage example see @ref samples/tcp_full_duplex_service/main.cpp
template <typename Metric>
class MetricTag final {
public:
    /// Register metric, passing a copy of `args` to the constructor of `Metric`
    template <typename... Args>
    explicit MetricTag(std::string path, Args&&... args) : key_{typeid(Metric), std::move(path)} {
        impl::RegisterMetricInfo(key_, impl::MakeMetricFactory<Metric>(std::forward<Args>(args)...));
    }
 
    std::string GetPath() const { return key_.path; }
 
private:
    friend class MetricsStorage;
 
    const impl::MetricKey key_;
};
 
}  // namespace utils::statistics
 
USERVER_NAMESPACE_END