granicus.if.org Git - icinga2/blob - lib/base/lazy-init.hpp

   1 /******************************************************************************
   2  * Icinga 2                                                                   *
   3  * Copyright (C) 2012-2018 Icinga Development Team (https://icinga.com/)      *
   4  *                                                                            *
   5  * This program is free software; you can redistribute it and/or              *
   6  * modify it under the terms of the GNU General Public License                *
   7  * as published by the Free Software Foundation; either version 2             *
   8  * of the License, or (at your option) any later version.                     *
   9  *                                                                            *
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  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the              *
  13  * GNU General Public License for more details.                               *
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.             *
  18  ******************************************************************************/
  19
  20 #ifndef LAZY_INIT
  21 #define LAZY_INIT
  22
  23 #include <atomic>
  24 #include <functional>
  25 #include <mutex>
  26 #include <utility>
  27
  28 namespace icinga
  29 {
  30
  31 /**
  32  * Lazy object initialization abstraction inspired from
  33  * <https://docs.microsoft.com/en-us/dotnet/api/system.lazy-1?view=netframework-4.7.2>.
  34  *
  35  * @ingroup base
  36  */
  37 template<class T>
  38 class LazyInit
  39 {
  40 public:
  41         inline
  42         LazyInit(std::function<T()> initializer = []() { return T(); }) : m_Initializer(std::move(initializer))
  43         {
  44                 m_Underlying.store(nullptr, std::memory_order_release);
  45         }
  46
  47         LazyInit(const LazyInit&) = delete;
  48         LazyInit(LazyInit&&) = delete;
  49         LazyInit& operator=(const LazyInit&) = delete;
  50         LazyInit& operator=(LazyInit&&) = delete;
  51
  52         inline
  53         ~LazyInit()
  54         {
  55                 auto ptr (m_Underlying.load(std::memory_order_acquire));
  56
  57                 if (ptr != nullptr) {
  58                         delete ptr;
  59                 }
  60         }
  61
  62         inline
  63         T& Get()
  64         {
  65                 auto ptr (m_Underlying.load(std::memory_order_acquire));
  66
  67                 if (ptr == nullptr) {
  68                         std::unique_lock<std::mutex> lock (m_Mutex);
  69
  70                         ptr = m_Underlying.load(std::memory_order_acquire);
  71
  72                         if (ptr == nullptr) {
  73                                 ptr = new T(m_Initializer());
  74                                 m_Underlying.store(ptr, std::memory_order_release);
  75                         }
  76                 }
  77
  78                 return *ptr;
  79         }
  80
  81 private:
  82         std::function<T()> m_Initializer;
  83         std::mutex m_Mutex;
  84         std::atomic<T*> m_Underlying;
  85 };
  86
  87 }
  88
  89 #endif /* LAZY_INIT */