ifstream 线程安全读文件

std::istream& safeGetline(std::istream& is, std::string& t)
{
    t.clear();

    //这比使用std::istream逐个读取它们要快。 
	//以这种方式使用streambuf的代码必须由sentry对象保护。 
	// sentry对象执行各种任务，如线程同步和更新流状态。

    std::istream::sentry se(is, true);
    std::streambuf* sb = is.rdbuf();

    for(;;) {
        int c = sb->sbumpc();
        switch (c) {
        case '\r':
            c = sb->sgetc();
            if(c == '\n')
                sb->sbumpc();
            return is;
        case '\n':
        case EOF:
            return is;
        default:
            t += (char)c;
        }
    }
}

int main()
{
    std::string path = "end_of_line_test.txt"

    std::ifstream ifs(path.c_str());
    if(!ifs) {
        std::cout << "Failed to open the file." << std::endl;
        return EXIT_FAILURE;
    }

    int n = 0;
    std::string t;
    while(safeGetline(ifs, t))   //<---- INFINITE LOOP happens here. <----
        std::cout << "\nLine " << ++n << ":" << t << std::endl;

    std::cout << "\nThe file contains " << n << " lines." << std::endl;
    return EXIT_SUCCESS;
}