线程本地存储单例类：针对“每个结构”每个线程仅有一个线程本地存储类对象
t_value_:类型为T的指针是pod类型可以用__thread修饰，每个线程一份
deleter：Deleter类对象
instance():返回T引用
pointer()：返回T指针
destructor():借助Deleter才能被调用
Deleter类：嵌套在ThreadLocalSingleton类中，借助于TSD实现线程本地存储机制
Show Me The Code：
// 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 <boost/noncopyable.hpp>
#include <assert.h>
#include <pthread.h>
namespace muduo
{
template<typename T>
class ThreadLocalSingleton : boost::noncopyable
{
public:
static T& instance()
{
if (!t_value_)
{
t_value_ = new T();
deleter_.set(t_value_);
}
return *t_value_;//每个线程都有一份自己的指针，因此不需要按照线程安全的方式实现
}
static T* pointer()
{
return t_value_;
}
private:
static void destructor(void* obj)
{
assert(obj == t_value_);
typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
delete t_value_;//销毁key对应的值
t_value_ = 0;
}
class Deleter//主要为了能够回调destructor--动态销毁key对应的值
{
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_;//线程本地存储--类型为T的指针，每个线程有一份
static Deleter deleter_;//Deleter是线程本地存储类，deleter_每个线程一份，用于销毁t_value_指针所指向的对象
};
template<typename T>
__thread T* ThreadLocalSingleton<T>::t_value_ = 0;//静态类成员定义
template<typename T>
typename ThreadLocalSingleton<T>::Deleter ThreadLocalSingleton<T>::deleter_;//静态类成员定义
}
#endif
说明：ThreadLocalSingleton类的作用与 muduo库学习笔记十二：base库之threadLocal 中 使用示例2
#define STL muduo::Singleton<muduo::ThreadLocal<Test> >::instance().value()
的作用效果一样，但是一般使用前者。
使用示例：
#include <muduo/base/ThreadLocalSingleton.h>
#include <muduo/base/CurrentThread.h>
#include <muduo/base/Thread.h>
#include <boost/bind.hpp>
#include <boost/noncopyable.hpp>
#include <stdio.h>
class Test : boost::noncopyable
{
public:
Test()
{
printf("tid=%d, constructing %p\n", muduo::CurrentThread::tid(), this);
}
~Test()
{
printf("tid=%d, destructing %p %s\n", muduo::CurrentThread::tid(), this, name_.c_str());
}
const std::string& name() const { return name_; }
void setName(const std::string& n) { name_ = n; }
private:
std::string name_;
};
void threadFunc(const char* changeTo)
{
printf("tid=%d, %p name=%s\n",
muduo::CurrentThread::tid(),
&muduo::ThreadLocalSingleton<Test>::instance(),
muduo::ThreadLocalSingleton<Test>::instance().name().c_str());
muduo::ThreadLocalSingleton<Test>::instance().setName(changeTo);
printf("tid=%d, %p name=%s\n",
muduo::CurrentThread::tid(),
&muduo::ThreadLocalSingleton<Test>::instance(),
muduo::ThreadLocalSingleton<Test>::instance().name().c_str());
// no need to manually delete it
// muduo::ThreadLocalSingleton<Test>::destroy();
}
int main()
{
muduo::ThreadLocalSingleton<Test>::instance().setName("main one");
/*
与 muduo库学习笔记十二：base库之threadLocal 使用示例1：
相比较进行说明
muduo::ThreadLocal<Test> testObj1;//线程本地存储类对象1
muduo::ThreadLocal<Test> testObj2;//线程本地存储类对象2
ThreadLocalSingleton类使用针对“每个结构”每个线程仅有一个线程本地存储类对象
*/
muduo::Thread t1(boost::bind(threadFunc, "thread1"));
muduo::Thread t2(boost::bind(threadFunc, "thread2"));
t1.start();
t2.start();
t1.join();
printf("tid=%d, %p name=%s\n",
muduo::CurrentThread::tid(),
&muduo::ThreadLocalSingleton<Test>::instance(),
muduo::ThreadLocalSingleton<Test>::instance().name().c_str());
t2.join();
pthread_exit(0);
}
结果：