查看“︁Boost:共享锁”︁的源代码

=示例代码=
<source lang="cpp">
#include <iostream>
#include <boost/thread.hpp>
#include <windows.h>

int sum = 0;
boost::shared_mutex  mu;

int write(int c){
	for (int i = 0; i < c; i++){
		boost::unique_lock<boost::shared_mutex> lock(mu);
		sum++;
		cout << "=>" << sum << endl;
	}
	return sum;
}
void read(int nCount){
	for (int i = 0; i < nCount; i++){
		boost::shared_lock<boost::shared_mutex> lock(mu);
		cout << "<=" << sum << endl;
	}
}
int main(int argc, char* argv[]) {
	boost::thread t1(write, 100);
	boost::thread t2(read, 100);
	boost::thread t3(read, 100);
	t1.join();
	t2.join();
	t3.join();
	system("pause");
	return 1;
}
</source>

=代码分析=
如果屏蔽掉上述代码两处加锁的地方，会出现什么情况？
*第一次
[[Image:Test_Thread_ts1.png|600px]]
*第二次
[[Image:Test_Thread_ts2.png|600px]]

可以看出，这两处地方读取到的数值是不对的，可能是在写的同时，正好读取到了脏数据。如果加上锁，结果才会如预期一样，是依次递增的。
[[Category:Programe]]