cache_update_trait.hpp

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#pragma once
 
/// @file userver/cache/cache_update_trait.hpp
/// @brief @copybrief cache::CacheUpdateTrait
 
#include <memory>
#include <string>
 
#include <userver/cache/cache_statistics.hpp>
#include <userver/cache/update_type.hpp>
#include <userver/components/component_fwd.hpp>
#include <userver/dump/fwd.hpp>
#include <userver/engine/task/task_processor_fwd.hpp>
#include <userver/rcu/fwd.hpp>
#include <userver/utils/flags.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace cache {
 
struct CacheDependencies;
struct Config;
 
/// @ingroup userver_base_classes
///
/// @brief Base class for periodically updated caches.
///
/// @note Don't use directly, inherit from components::CachingComponentBase
/// instead
class CacheUpdateTrait {
 public:
  CacheUpdateTrait(CacheUpdateTrait&&) = delete;
  CacheUpdateTrait& operator=(CacheUpdateTrait&&) = delete;
 
  /// @brief Non-blocking forced cache update of specified type
  /// @see PeriodicTask::ForceStepAsync for behavior details
  void InvalidateAsync(UpdateType update_type);
 
  /// @brief Forces a cache update of specified type
  /// @throws If `Update` throws
  void UpdateSyncDebug(UpdateType update_type);
 
  /// @return name of the component
  const std::string& Name() const;
 
 protected:
  /// @cond
  // For internal use only
  CacheUpdateTrait(const components::ComponentConfig& config,
                   const components::ComponentContext& context);
 
  // For internal use only
  explicit CacheUpdateTrait(CacheDependencies&& dependencies);
 
  virtual ~CacheUpdateTrait();
  /// @endcond
 
  /// Update types configured for the cache
  AllowedUpdateTypes GetAllowedUpdateTypes() const;
 
  /// Periodic update flags
  enum class Flag {
    kNone = 0,
    kNoFirstUpdate = 1 << 0,  ///< Disable initial update on start
  };
 
  /// Starts periodic updates
  void StartPeriodicUpdates(utils::Flags<Flag> flags = {});
 
  /// @brief Stops periodic updates
  /// @warning Should be called in destructor of derived class.
  void StopPeriodicUpdates();
 
  void AssertPeriodicUpdateStarted();
 
  /// Called in `CachingComponentBase::Set` during update to indicate
  /// that the cached data has been modified
  void OnCacheModified();
 
  /// @cond
  // For internal use only
  rcu::ReadablePtr<Config> GetConfig() const;
 
  // Checks for the presence of the flag for pre-assign check.
  // For internal use only.
  bool HasPreAssignCheck() const;
 
  // For internal use only.
  void SetDataSizeStatistic(std::size_t size) noexcept;
 
  // For internal use only
  // TODO remove after TAXICOMMON-3959
  engine::TaskProcessor& GetCacheTaskProcessor() const;
  /// @endcond
 
  /// @brief Should be overridden in a derived class to align the stored data
  /// with some data source.
  ///
  /// `Update` implementation should do one of the following:
  ///
  /// A. If the update succeeded and has changes...
  ///    1. call CachingComponentBase::Set to update the stored value and send a
  ///    notification to subscribers
  ///    2. call UpdateStatisticsScope::Finish
  ///    3. return normally (an exception is allowed in edge cases)
  /// B. If the update succeeded and verified that there are no changes...
  ///    1. DON'T call CachingComponentBase::Set
  ///    2. call UpdateStatisticsScope::FinishNoChanges
  ///    3. return normally (an exception is allowed in edge cases)
  /// C. If the update failed...
  ///    1. DON'T call CachingComponentBase::Set
  ///    2. call UpdateStatisticsScope::FinishWithError, or...
  ///    3. throw an exception, which will be logged nicely
  ///
  /// @param type type of the update
  /// @param last_update time of the last update (value of `now` from previous
  /// invocation of Update or default constructed value if this is the first
  /// Update).
  /// @param now current time point
  ///
  /// @throws std::exception on update failure
  ///
  /// @warning If `Update` returns without throwing an exception and without
  /// calling one of the `Finish*` methods, the behavior is undefined.
  ///
  /// @see @ref scripts/docs/en/userver/caches.md
  virtual void Update(UpdateType type,
                      const std::chrono::system_clock::time_point& last_update,
                      const std::chrono::system_clock::time_point& now,
                      UpdateStatisticsScope& stats_scope) = 0;
 
 private:
  virtual void Cleanup() = 0;
 
  virtual void MarkAsExpired();
 
  virtual void GetAndWrite(dump::Writer& writer) const;
 
  virtual void ReadAndSet(dump::Reader& reader);
 
  class Impl;
  std::unique_ptr<Impl> impl_;
};
 
}  // namespace cache
 
USERVER_NAMESPACE_END