text: // Use of this source code is governed by a BSD-style license
  // that can be found in the License file.
  //
  // Author: Shuo Chen (chenshuo at chenshuo dot com)
  
  #ifndef MUDUO_BASE_THREADLOCALSINGLETON_H
  #define MUDUO_BASE_THREADLOCALSINGLETON_H
  
  #include "muduo/base/noncopyable.h"
  
  #include <assert.h>
  #include <pthread.h>
  
  namespace muduo
  {
  
  template<typename T>
  class ThreadLocalSingleton : noncopyable
  {
   public:
    ThreadLocalSingleton() = delete;
    ~ThreadLocalSingleton() = delete;
  // 返回单例对象的引用
    static T& instance()
    {
      if (!t_value_)
      {
        t_value_ = new T();
        deleter_.set(t_value_);
      }
      return *t_value_;
    }
  //返回对象的指针
    static T* pointer()
    {
      return t_value_;
    }
  
   private:
   //销毁对象
    static void destructor(void* obj)
    {
      assert(obj == t_value_);
      typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
      T_must_be_complete_type dummy; (void) dummy;
      delete t_value_;
      t_value_ = 0;
    }
  
    class Deleter
    {
     public:
      Deleter()
      {
        pthread_key_create(&pkey_, &ThreadLocalSingleton::destructor);
      }
  
      ~Deleter()
      {
        pthread_key_delete(pkey_);
      }
  
      void set(T* newObj)
      {
        assert(pthread_getspecific(pkey_) == NULL);
        pthread_setspecific(pkey_, newObj);
      }
  
      pthread_key_t pkey_;
    };
  
    static __thread T* t_value_;
    static Deleter deleter_;
  };
  
  template<typename T>
  __thread T* ThreadLocalSingleton<T>::t_value_ = 0;
  
  template<typename T>
  typename ThreadLocalSingleton<T>::Deleter ThreadLocalSingleton<T>::deleter_;
  
  }  // namespace muduo
  #endif  // MUDUO_BASE_THREADLOCALSINGLETON_H
  