retry_budget.hpp

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#pragma once
 
/// @file userver/utils/retry_budget.hpp
/// @brief @copybrief utils::RetryBudget
 
#include <atomic>
#include <cstdint>
 
#include <userver/formats/json_fwd.hpp>
#include <userver/formats/parse/to.hpp>
#include <userver/utils/statistics/rate_counter.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
namespace statistics {
class Writer;
}
 
struct RetryBudgetSettings final {
  // Maximum number of tokens in the budget.
  float max_tokens{100.0f};
  // The number of tokens by which the budget will be increased in case of a
  // successful request.
  float token_ratio{0.1f};
  // Enable/disable retry budget.
  bool enabled{true};
};
 
/// Class implements the same logic described in
/// https://github.com/grpc/proposal/blob/master/A6-client-retries.md#throttling-configuration
class RetryBudget final {
 public:
  RetryBudget();
  explicit RetryBudget(const RetryBudgetSettings& settings);
 
  /// Call after a request succeeds.
  void AccountOk() noexcept;
 
  /// Call after a request fails.
  void AccountFail() noexcept;
 
  /// @brief Call before attempting a retry (but not before the initial
  /// request).
  bool CanRetry() const;
 
  /// Thread-safe relative to AccountOk/AccountFail/CanRetry.
  /// Not thread-safe relative other SetSettings method calls.
  void SetSettings(const RetryBudgetSettings& settings);
 
 private:
  std::atomic<std::uint32_t> max_tokens_;
  std::atomic<std::uint32_t> token_ratio_;
  std::atomic<std::int32_t> token_count_;
  std::atomic<bool> enabled_{false};
 
  // rate of account oks
  utils::statistics::RateCounter ok_rate_counter_;
  // rate of account fails
  utils::statistics::RateCounter fail_rate_counter_;
 
  friend void DumpMetric(statistics::Writer& writer, const RetryBudget& budget);
};
 
RetryBudgetSettings Parse(const formats::json::Value& elem,
                          formats::parse::To<RetryBudgetSettings>);
 
}  // namespace utils
 
USERVER_NAMESPACE_END