struct my_class
{
    mutable boost::mutex m;
    int x,y;
};
bool operator<(my_class const& lhs,my_class const& rhs)
{
    boost::lock(lhs.m,rhs.m);
    boost::mutex::scoped_lock lk1(lhs.m,boost::adopt_lock);
    boost::mutex::scoped_lock lk2(rhs.m,boost::adopt_lock);
    return (lhs.x<rhs.x) ||
           ((lhs.x==rhs.x) && (lhs.y<rhs.y));
}