1 // Copyright (C) 2020 The Libphonenumber Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef I18N_PHONENUMBERS_BASE_MEMORY_SINGLETON_STDMUTEX_H_ 16 #define I18N_PHONENUMBERS_BASE_MEMORY_SINGLETON_STDMUTEX_H_ 17 18 #include <mutex> 19 20 #include "phonenumbers/base/basictypes.h" 21 22 namespace i18n { 23 namespace phonenumbers { 24 25 template <class T> 26 class Singleton { 27 public: Singleton()28 Singleton() {} ~Singleton()29 virtual ~Singleton() {} 30 GetInstance()31 static T* GetInstance() { 32 if (once_init_) { 33 singleton_mutex_.lock(); 34 if (once_init_) { 35 Init(); 36 once_init_ = false; 37 } 38 singleton_mutex_.unlock(); 39 } 40 return instance_; 41 } 42 43 private: 44 DISALLOW_COPY_AND_ASSIGN(Singleton); 45 Init()46 static void Init() { 47 instance_ = new T(); 48 } 49 50 static T* instance_; // Leaky singleton. 51 static std::mutex singleton_mutex_; 52 static bool once_init_; 53 }; 54 55 template <class T> T* Singleton<T>::instance_; 56 template <class T> std::mutex Singleton<T>::singleton_mutex_; 57 template <class T> bool Singleton<T>::once_init_ = true; 58 59 } // namespace phonenumbers 60 } // namespace i18n 61 62 #endif // I18N_PHONENUMBERS_BASE_MEMORY_SINGLETON_STDMUTEX_H_ 63