muduo库源码学习(base)ThreadLocalSingleton

// 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//线程局部的单例，也就是每个线程一个T。static __thread T* t_value_;{ public:  static T& instance()  {    if (!t_value_)    {      t_value_ = new T();      deleter_.set(t_value_);//内存交给deleter释放    }    return *t_value_;  }  static T* pointer()  {    return t_value_;  } private:  ThreadLocalSingleton();  ~ThreadLocalSingleton();  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_;//__thread无法调用class的析构  static Deleter deleter_;//wow!只有一个Deleter,程序结束时，它析构自己时通知系统执行destructor,一次性删除所有内存};template<typename T>__thread T* ThreadLocalSingleton<T>::t_value_ = 0;template<typename T>typename ThreadLocalSingleton<T>::Deleter ThreadLocalSingleton<T>::deleter_;}#endif