relaxed_counter.hpp

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#pragma once
 
/// @file userver/utils/statistics/relaxed_counter.hpp
/// @brief @copybrief utils::statistics::RelaxedCounter
 
#include <atomic>
 
#include <userver/utils/statistics/fwd.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils::statistics {
 
/// @brief Atomic counter of type T with relaxed memory ordering
template <class T>
class RelaxedCounter final {
public:
    using ValueType = T;
 
    constexpr RelaxedCounter() noexcept = default;
    constexpr RelaxedCounter(T desired) noexcept : val_(desired) {}
 
    RelaxedCounter(const RelaxedCounter& other) noexcept : val_(other.Load()) {}
 
    RelaxedCounter& operator=(const RelaxedCounter& other) noexcept {
        if (this == &other) return *this;
 
        Store(other.Load());
        return *this;
    }
 
    RelaxedCounter& operator=(T desired) noexcept {
        Store(desired);
        return *this;
    }
 
    void Store(T desired) noexcept { val_.store(desired, std::memory_order_relaxed); }
 
    T Load() const noexcept { return val_.load(std::memory_order_relaxed); }
 
    operator T() const noexcept { return Load(); }
 
    RelaxedCounter& operator++() noexcept {
        val_.fetch_add(1, std::memory_order_relaxed);
        return *this;
    }
 
    T operator++(int) noexcept { return val_.fetch_add(1, std::memory_order_relaxed); }
 
    RelaxedCounter& operator--() noexcept {
        val_.fetch_sub(1, std::memory_order_relaxed);
        return *this;
    }
 
    T operator--(int) noexcept { return val_.fetch_sub(1, std::memory_order_relaxed); }
 
    RelaxedCounter& operator+=(T arg) noexcept {
        val_.fetch_add(arg, std::memory_order_relaxed);
        return *this;
    }
 
    RelaxedCounter& operator-=(T arg) noexcept {
        val_.fetch_sub(arg, std::memory_order_relaxed);
        return *this;
    }
 
private:
    static_assert(std::atomic<T>::is_always_lock_free);
 
    std::atomic<T> val_{T{}};
};
 
template <typename T>
void DumpMetric(Writer& writer, const RelaxedCounter<T>& value) {
    writer = value.Load();
}
 
}  // namespace utils::statistics
 
USERVER_NAMESPACE_END