c++11的mutex

#include <mutex>
#include <list>
std::list<int> _list;
std::mutex _mutex;
void addList(int iValue)
{
std::lock_guard<std::mutex> guard(_mutex);
_list.push_back(iValue);
}

bool list_contain(int valueToFind)
{
std::lock_guard<std::mutex> guard(_mutex);
return std::find(_list.begin(),_list.end(),valueToFind)!=_list.end();
}