共享互斥量shared_mutex允许线程获取多个共享所有权shared_lock和一个专享所有权uique_lock，实现了读写锁机制，即多个读线程一个写线程。
~~~
#include "stdafx.h"
#include <iostream>
#include <boost/thread.hpp>
#include <boost/atomic.hpp>
boost::mutex io_mu;//io读写锁
class rw_data
{
public:
rw_data():m_x(0){}//构造函数
void write()//写数据
{
boost::unique_lock<boost::shared_mutex> ul(rw_mu);//写锁定,使用unique_lock<shared_mutex>
++m_x;
}
void read(int *x)//读数据
{
boost::shared_lock<boost::shared_mutex> sl(rw_mu);//读锁定，使用shared_lock<shared_mutex>
*x=m_x;
}
private:
int m_x;//用于读写的数据变量
boost::shared_mutex rw_mu;//共享互斥量
};
//定义用于线程执行的多次读写函数
void writer(rw_data &d)
{
for(int i=0;i<10;++i)
{
boost::this_thread::sleep(boost::posix_time::millisec(10));//休眠
d.write();
}
}
void reader(rw_data &d)
{
int x=0;
for(int i=0;i<10;++i)
{
boost::this_thread::sleep(boost::posix_time::millisec(5));//休眠
d.read(&x);
boost::mutex::scoped_lock lock(io_mu);//锁定IO
std::cout<<"reader:"<<x<<std::endl;
}
}
int _tmain(int argc, _TCHAR* argv[])
{
rw_data d;
boost::thread_group tg;
tg.create_thread(boost::bind(reader,boost::ref(d)));
tg.create_thread(boost::bind(reader,boost::ref(d)));
tg.create_thread(boost::bind(reader,boost::ref(d)));
tg.create_thread(boost::bind(reader,boost::ref(d)));
tg.create_thread(boost::bind(writer,boost::ref(d)));
tg.create_thread(boost::bind(writer,boost::ref(d)));
tg.create_thread(boost::bind(writer,boost::ref(d)));
tg.create_thread(boost::bind(writer,boost::ref(d)));
tg.join_all();
getchar();
return 0;
}
~~~
