Boost:共享锁

示例代码

#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;
}

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

• 第二次