ut0object_cache.h

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/** @file include/ut0object_cache.h
Manage a cache of objects. */
 
#ifndef ut0object_cache_h
#define ut0object_cache_h
 
#include "ut0new.h"
 
namespace ut {
 
/** A class to manage objects of type T. */
template <typename T>
class Object_cache {
 public:
  /** Destructor. Frees the cached objects. */
  ~Object_cache() {
    for (auto obj : m_objects) {
      ut::delete_(obj);
    }
  }
 
  /** Initialize the cache.
  @param[in]  size   initial number of objects to cache.
  @param[in]  step   when extending cache, number of objects to add.
  @param[in]  args   arguments to be passed to constructor of T */
  template <typename... Types>
  dberr_t init(size_t size, size_t step, Types &&...args) {
    m_step = step;
    return extend(size, std::forward<Types>(args)...);
  }
 
  template <typename... Types>
  T *allocate(Types &&...args) {
    if (m_index == m_objects.size()) {
      extend(m_step, std::forward<Types>(args)...);
    }
    /* Could set m_objects[m_index] to nullptr, but not required. */
    return m_objects[m_index++];
  }
 
  template <typename... Types>
  dberr_t extend(size_t size, Types &&...args) {
    m_objects.reserve(m_objects.size() + size);
    for (size_t i = 0; i < size; ++i) {
      auto obj = ut::new_withkey<T>(UT_NEW_THIS_FILE_PSI_KEY,
                                    std::forward<Types>(args)...);
      if (obj == nullptr) {
        /* dtor will free all allocated objects. */
        return DB_OUT_OF_MEMORY;
      }
      m_objects.push_back(obj);
    }
    return DB_SUCCESS;
  }
 
  void deallocate(T *obj) {
    ut_ad(m_index > 0);
    m_objects[--m_index] = obj;
  }
 
 private:
  /** Cached objects. */
  std::vector<T *> m_objects;
 
  /** When the cache is extended, how many new objects needs to be created. */
  size_t m_step{1};
 
  /** Position of next object to be allocated. */
  size_t m_index{0};
};
 
}  // namespace ut
 
#endif /* ut0object_cache_h */