statistics_instance_monitor.h

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#ifndef MYSQL_SCHEDULER_STATISTICS_INSTANCE_MONITOR_H
#define MYSQL_SCHEDULER_STATISTICS_INSTANCE_MONITOR_H
 
#include <atomic>
#include <chrono>
#include <functional>
#include <memory>
#include <optional>
#include <unordered_map>
#include "mysql/concurrency/condition_variable.h"
#include "mysql/concurrency/mutex.h"
#include "mysql/scheduler/constants.h"
#include "mysql/scheduler/sharded_counter.h"
#include "mysql/scheduler/statistics_type_traits.h"
 
namespace mysql::scheduler {
 
class Statistics_instance_monitor;
using Statistics_instance_monitor_ref =
    std::reference_wrapper<Statistics_instance_monitor>;
 
/// @brief CSA statistics monitor, gathers statistics coming from different
/// CSA threads
/// Each statistic is a pair of key (statistic string) and value. This will
/// help with backward and forward compatibility of statistics implemented
/// in CSA servis w.r.t. statistics supported in the server
/// Statistic update method ingests thread id, to keep a sharded statistics
/// value until coalescing operation requested by external thread to
/// get accumulated value (if coalescing is requested during "get" operation).
/// For the time being, we assume only 1 channel
class Statistics_instance_monitor {
 public:
  using Mutex = concurrency::Mutex;
  using Mutex_key = concurrency::Mutex_key;
 
  void init();
 
  /// @brief Get statistic value
  /// @param name Name of statistic
  /// @param thread_num The number of threads accessing statistic
  /// @param enable Information on whether to enable this particular statistic
  template <Statistic_allowed_type Type = long long>
  void register_stat(const std::string &name, std::size_t thread_num = 1,
                     bool enable = true);
  /// @brief Get accumulated statistic value
  /// @param name Name of statistic
  /// @return Value if statistic is found, no value otherwise
  template <Statistic_allowed_type Type = long long>
  std::optional<
      std::reference_wrapper<typename Statistic_type_traits<Type>::type>>
  find_stat(const std::string &name);
  /// @brief Get accumulated statistic value w/o bound checking
  /// @param name Name of statistic
  /// @return Value if statistic is found, no value otherwise w/o bound checking
  template <Statistic_allowed_type Type = long long>
  typename Statistic_type_traits<Type>::type &get_stat(const std::string &name);
 
  /// @brief Resets initialized statistics, use wisely
  void reset();
  /// @brief Frees registered statistics storage for this instance
  void clear();
 
  Statistics_instance_monitor() = default;
 
 protected:
  using Registry_type = std::unordered_map<std::string, Sharded_counter>;
  Registry_type m_registry;
};
 
}  // namespace mysql::scheduler
 
#include "mysql/scheduler/statistics_instance_monitor_impl.hpp"
 
#endif  // MYSQL_SCHEDULER_STATISTICS_INSTANCE_MONITOR_H