提升精神:缓慢的解析优化

时间:2015-10-06 11:07:02

标签: c++ parsing boost-spirit qi

我是灵魂的新手和一般的提升。我试图解析一个看起来像这样的VRML文件:

point
            [
            #coordinates written in meters.
            -3.425386e-001 -1.681608e-001 0.000000e+000,
            -3.425386e-001 -1.642545e-001 0.000000e+000,
            -3.425386e-001 -1.603483e-001 0.000000e+000,

开头的评论是可选的。

我已经编写了一个语法,但工作正常,但解析过程需要很长时间。我想优化它以更快地运行。我的代码如下所示:

struct Point
{
    double a;
    double b;
    double c;

    Point() : a(0.0), b(0.0), c(0.0){}
};

BOOST_FUSION_ADAPT_STRUCT
(
    Point,
    (double, a) 
    (double, b)
    (double, c)
)

namespace qi   = boost::spirit::qi;
namespace repo = boost::spirit::repository;

template <typename Iterator>
struct PointParser : 
public qi::grammar<Iterator, std::vector<Point>(), qi::space_type>
{
   PointParser() : PointParser::base_type(start, "PointGrammar")
   {
      singlePoint = qi::double_>>qi::double_>>qi::double_>>*qi::lit(",");
      comment = qi::lit("#")>>*(qi::char_("a-zA-Z.") - qi::eol);
      prefix = repo::seek[qi::lexeme[qi::skip[qi::lit("point")>>qi::lit("[")>>*comment]]];
      start %= prefix>>qi::repeat[singlePoint];     

      //BOOST_SPIRIT_DEBUG_NODES((prefix)(comment)(singlePoint)(start));
   }

   qi::rule<Iterator, Point(), qi::space_type>              singlePoint;
   qi::rule<Iterator, qi::space_type>                       comment;
   qi::rule<Iterator, qi::space_type>                       prefix;
   qi::rule<Iterator, std::vector<Point>(), qi::space_type> start;
};

我打算解析的部分位于输入文本的中间,所以我需要跳过文本的一部分才能找到它。我使用 repo :: seek 实现了它。这是最好的方法吗?

我按以下方式运行解析器:

std::vector<Point> points;
typedef PointParser<std::string::const_iterator> pointParser;   
pointParser g2; 

auto start = ch::high_resolution_clock::now();  
bool r = phrase_parse(Data.begin(), Data.end(), g2, qi::space, points); 
auto end = ch::high_resolution_clock::now();

auto duration = ch::duration_cast<boost::chrono::milliseconds>(end - start).count();

要解析输入文本中的大约80k条目,大约需要2.5秒,这对我的需求来说非常慢。我的问题是有一种方法以更优化的方式编写解析规则,使其(更快)更快?我如何改进这种实施?

我是Spirit的新手,所以我们将非常感谢您的一些解释。

1 个答案:

答案 0 :(得分:2)

我已将您的语法挂钩到Nonius基准测试,并生成约85k行的均匀随机输入数据(下载:http://stackoverflow-sehe.s3.amazonaws.com/input.txt,7.4 MB)。

  • 你在发布版本中测量时间吗?
  • 您使用的是慢速文件输入吗?

在预先阅读文件时,我总是得到 ~36ms 的时间来解析整个文件。

clock resolution: mean is 17.616 ns (40960002 iterations)

benchmarking sample
collecting 100 samples, 1 iterations each, in estimated 3.82932 s
mean: 36.0971 ms, lb 35.9127 ms, ub 36.4456 ms, ci 0.95
std dev: 1252.71 μs, lb 762.716 μs, ub 2.003 ms, ci 0.95
found 6 outliers among 100 samples (6%)
variance is moderately inflated by outliers

代码:见下文。

注意:

  • 你似乎在使用船长和一起寻求冲突。我建议您简化prefix

    comment     = '#' >> *(qi::char_ - qi::eol);
    
    prefix      = repo::seek[
                      qi::lit("point") >> '[' >> *comment
                  ];
    

    prefix将使用空格管理器,并忽略任何匹配的属性(因为规则声明了类型)。通过从规则声明中删除队长来隐式地使comment成为 lexeme

        // implicit lexeme:
        qi::rule<Iterator>                       comment;
    
      

    注意有关更多背景信息,请参阅Boost spirit skipper issues

<强> Live On Coliru

#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/repository/include/qi_seek.hpp>

namespace qi   = boost::spirit::qi;
namespace repo = boost::spirit::repository;

struct Point { double a = 0, b = 0, c = 0; };

BOOST_FUSION_ADAPT_STRUCT(Point, a, b, c)

template <typename Iterator>
struct PointParser : public qi::grammar<Iterator, std::vector<Point>(), qi::space_type>
{
    PointParser() : PointParser::base_type(start, "PointGrammar")
    {
        singlePoint = qi::double_ >> qi::double_ >> qi::double_ >> *qi::lit(',');

        comment     = '#' >> *(qi::char_ - qi::eol);

        prefix      = repo::seek[
            qi::lit("point") >> '[' >> *comment
            ];

        //prefix      = repo::seek[qi::lexeme[qi::skip[qi::lit("point")>>qi::lit("[")>>*comment]]];

        start      %= prefix >> *singlePoint;

        //BOOST_SPIRIT_DEBUG_NODES((prefix)(comment)(singlePoint)(start));
    }

  private:
    qi::rule<Iterator, Point(), qi::space_type>              singlePoint;
    qi::rule<Iterator, std::vector<Point>(), qi::space_type> start;
    qi::rule<Iterator, qi::space_type>                       prefix;
    // implicit lexeme:
    qi::rule<Iterator>  comment;
};

#include <nonius/benchmark.h++>
#include <nonius/main.h++>
#include <boost/iostreams/device/mapped_file.hpp>

static boost::iostreams::mapped_file_source src("input.txt");

NONIUS_BENCHMARK("sample", [](nonius::chronometer cm) {
    std::vector<Point> points;

    using It = char const*;
    PointParser<It> g2;

    cm.measure([&](int) {
        It f = src.begin(), l = src.end();
        return phrase_parse(f, l, g2, qi::space, points);
        bool ok =  phrase_parse(f, l, g2, qi::space, points);
        if (ok)
            std::cout << "Parsed " << points.size() << " points\n";
        else
            std::cout << "Parsed failed\n";

        if (f!=l)
            std::cout << "Remaining unparsed input: '" << std::string(f,std::min(f+30, l)) << "'\n";

        assert(ok);
    });
})

图表:

enter image description here

另一个运行输出,live: