使用替代解析器提高精神不佳的表现

2021-12-24 00:00:00 c++ boost boost-spirit boost-spirit-qi

我已经问过关于这个问题的问题.但由于没有答案，我现在再次询问完整的可编译源代码片段.

I already asked question about this issue. But since there were no answers i'm asking again now with full compilable source code snippet.

由于 boost::variant 移动语义的一些问题，此代码片段应在不使用 std=c++11 选项的情况下进行编译.只是'g++ -Wall -pedantic'.

This code snippet should be compiled with no std=c++11 option, because of some issues with boost::variant move semantic. Just 'g++ -Wall -pedantic'.

在此代码片段中，您将找到//Comment here"行.您可以评论以下块，直到//And here -----".如果取消注释该块，则该程序的性能很差.

In this code snippet you will find "// Comment here" line. You can comment following block till "// And here -----". If this block is uncommented, performance of this program is very poor.

所以只要我能看到瓶颈是替代解析器.我需要的是一些关于改进/更改语法以提高解析性能的建议.谢谢.

So the bottleneck as long as i can see is alternative parser. What i need is some suggestions on improving/changing my grammar to improve parse perfomance. Thanks.

代码:

#include <string>
#include <vector>
#include <iostream>

#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/phoenix_statement.hpp>
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_object.hpp>
#include <boost/spirit/include/phoenix_function.hpp>
#include <boost/spirit/include/phoenix_fusion.hpp>
#include <boost/spirit/include/phoenix_stl.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/variant.hpp>
#include <boost/variant/recursive_wrapper.hpp>
#include <boost/array.hpp>
#include <boost/variant/apply_visitor.hpp>

namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
namespace phoenix = boost::phoenix;

namespace client {
  typedef std::string::iterator input_iterator_type;

  struct op_and {}; 
  struct op_or {};
  struct op_eq {};
  struct op_neq {};
  struct is_part_of {};
  struct more {};
  struct more_eq {};
  struct less {};
  struct less_eq {};
  struct mask_match {};
  struct mask_not_match {};
  struct in {};

 namespace type {
    enum code_t {
      string       = 0,
      boolean      = 1,
      number       = 2,
      none         = 3,
      datetime     = 4,
      unknown      = 5
    }; 
  }

  template <typename tag>  struct binop;
  struct   fn_call;
  struct   none_type {~none_type(){}};

  struct datetime {
    datetime(int yyyy, int mm, int dd, int hh24, int mi, int ss, int mls) 
      : yy(yyyy), mm(mm), dd(dd), hh(hh24), mi(mi), ss(ss), ms(mls) {}
    datetime()
      : yy(0), mm(0), dd(0), hh(0), mi(0), ss(0), ms(0) {}
    int yy; int mm; int dd;
    int hh; int mi; int ss;
    int ms;
  };

  typedef boost::variant<
    boost::recursive_wrapper<binop<op_and> >,
    boost::recursive_wrapper<binop<op_or> >,
    boost::recursive_wrapper<binop<op_eq> >,
    boost::recursive_wrapper<binop<op_neq> >,
    boost::recursive_wrapper<binop<is_part_of> >,
    boost::recursive_wrapper<binop<more> >,
    boost::recursive_wrapper<binop<more_eq> >,
    boost::recursive_wrapper<binop<less> >,
    boost::recursive_wrapper<binop<less_eq> >,
    boost::recursive_wrapper<binop<mask_match> >,
    boost::recursive_wrapper<binop<mask_not_match> >,
    boost::recursive_wrapper<binop<in> >
  > generic_binop;

  typedef boost::variant <
    std::string, double, none_type, datetime,
    boost::recursive_wrapper<generic_binop>,
    boost::recursive_wrapper<fn_call>
  > node_value_t;

  struct g_node {
    mutable type::code_t type_id; 
    mutable node_value_t value;
  };

  typedef node_value_t value_type;

  template <typename tag> struct binop { 
    explicit binop(const g_node& l, const g_node& r) 
      : oper1(l), oper2(r) {}
    g_node oper1, oper2; 
  };

  typedef std::vector<g_node> node_vector;

  struct fn_call {
    explicit fn_call(){}
    std::string name;
    node_vector params;
  };
}

BOOST_FUSION_ADAPT_STRUCT(
client::g_node,
(client::type::code_t, type_id)
(client::node_value_t, value)
)

BOOST_FUSION_ADAPT_STRUCT(
client::fn_call,
(std::string, name)
(std::vector<client::g_node>, params)
)

namespace client {

  template <typename Iterator> struct g_error_handler {
   template<typename, typename, typename, typename> 
    struct result { typedef void type; };

    void operator()(Iterator first, Iterator last,
          Iterator err_pos, boost::spirit::info const& what) const { 
      std::cout << "Syntax error. Expected: " << what << " at: " << 
        std::distance(first, err_pos) << std::endl;
    }
};

  template<typename Iterator, typename ErrorHandler = g_error_handler<Iterator> >
  struct g_parser : qi::grammar<Iterator, g_node(), ascii::space_type> {
    g_parser() : g_parser::base_type(or_, "G"), error_handler(ErrorHandler()) {

      using phoenix::at_c;

      or_ = (and_ >> "||" >> or_)[
        at_c<0>(qi::_val) = type::unknown, 
        at_c<1>(qi::_val) = phoenix::construct<binop<op_or> >(qi::_1, qi::_2)] |
        and_[qi::_val = qi::_1];

      and_ = (bool_op >> "&&" >> and_)[
        at_c<0>(qi::_val) = type::unknown, 
        at_c<1>(qi::_val) = phoenix::construct<binop<op_and> >(qi::_1, qi::_2)] |
        bool_op[qi::_val = qi::_1];

      bool_op = 
        (prim >> "=" >> bool_op)[
        at_c<0>(qi::_val) = type::unknown, 
        at_c<1>(qi::_val) = phoenix::construct<binop<op_eq> >(qi::_1, qi::_2)] |
        (prim >> "<>" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<op_neq> >(qi::_1, qi::_2)] |
          // Comment here ---------------------------------------------------
        (prim >> ":" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<is_part_of> >(qi::_1, qi::_2)] |
        (prim >> ">" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<more> >(qi::_1, qi::_2)] |
        (prim >> ">=" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<more_eq> >(qi::_1, qi::_2)] |
        (prim >> "<" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<less> >(qi::_1, qi::_2)] |
        (prim >> "<=" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<less_eq> >(qi::_1, qi::_2)] |
        (prim >> "=~" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<mask_match> >(qi::_1, qi::_2)] |
        (prim >> "!~" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<mask_not_match> >(qi::_1, qi::_2)] |
        (prim >> "in" >> bool_op)[
          at_c<0>(qi::_val) = type::unknown, 
          at_c<1>(qi::_val) = phoenix::construct<binop<in> >(qi::_1, qi::_2)] |
          // And here------------------------------------------------------------ 
        prim[qi::_val = qi::_1];

       prim = 
         string_val   [qi::_val =  qi::_1] |
         number       [qi::_val =  qi::_1] |
         func_call    [at_c<0>(qi::_val) = type::unknown, at_c<1>(qi::_val) =  qi::_1] | 
         '(' > or_    [qi::_val =  qi::_1] > ')';

       quoted_string %= "'" > qi::lexeme[*(qi::char_ - "'")] > "'";

       func_call = fn_name > '(' > -(or_ % ',') > ')';
       fn_name %= +(qi::alpha) > -(qi::char_('-')) > *(qi::alnum);

       string_val = quoted_string[
         at_c<0>(qi::_val) = type::string, at_c<1>(qi::_val) = qi::_1];

       number %= qi::attr(type::number) >> qi::double_;

       or_.name           ("OR expression"  );
       and_.name          ("AND expression" );
       bool_op.name       ("BOOL expression");
       prim.name          ("Atom expression");
       quoted_string.name ("quoted string"  );
       fn_name.name       ("function name"  );
       number.name        ("number"         );

       qi::on_error<qi::fail>(or_, error_handler(qi::_1, qi::_2, qi::_3, qi::_4));
    }

    qi::rule<Iterator, g_node(), ascii::space_type> 
      and_, bool_op, prim, or_, string_val, number;
    qi::rule<Iterator, fn_call(), ascii::space_type> func_call;
    qi::rule<Iterator, std::string(), ascii::space_type> quoted_string, fn_name;

    boost::phoenix::function<ErrorHandler> error_handler;
  };

  typedef g_parser<input_iterator_type> grammar;
}

int main() {
  std::string s = "((foo(bar('','')) = foo('')) || ('a' = 'gg')) && (3 <> 7) && (foo('','') = bar('','')) && 2=4 && 'a' ='b' && foo('') <> foo('')";
  client::grammar g;
  client::g_node ast;
  std::string::iterator begin = s.begin();
  std::string::iterator end = s.end();
  bool success = qi::phrase_parse(begin, end, g, 
    boost::spirit::ascii::space, ast) && begin == end;
  std::stringstream ss;
  if(!success)
    std::cout << "Syntax error at: " << std::distance(s.begin(), begin);
  else std::cout << "Syntax is Ok
";
}

推荐答案

您可以重构语法以减少回溯.我之前在 SO 上做过这样一个重构的例子.

You can refactor the grammar to induce less backtracking. I've done an example of such a refactoring before on SO.

链接:未找到

但是，这是要点.除了大大减少回溯的需要外，以下应该是等效的:

However, here's the gist. The following should be equivalent, except for the vastly reduced need to backtrack:

看到它在 Coliru 上直播

See it Live On Coliru

using boost::phoenix::construct;
using qi::_val;
using qi::_1;

bool_op =
    prim [ _val = _1 ] >> -((
    ("="  >> bool_op [ at_c<1>(_val) = construct<binop<op_eq> >          (_val, _1) ]) |
    ("<>" >> bool_op [ at_c<1>(_val) = construct<binop<op_neq> >         (_val, _1) ]) |
    (":"  >> bool_op [ at_c<1>(_val) = construct<binop<is_part_of> >     (_val, _1) ]) |
    (">"  >> bool_op [ at_c<1>(_val) = construct<binop<more> >           (_val, _1) ]) |
    (">=" >> bool_op [ at_c<1>(_val) = construct<binop<more_eq> >        (_val, _1) ]) |
    ("<"  >> bool_op [ at_c<1>(_val) = construct<binop<less> >           (_val, _1) ]) |
    ("<=" >> bool_op [ at_c<1>(_val) = construct<binop<less_eq> >        (_val, _1) ]) |
    ("=~" >> bool_op [ at_c<1>(_val) = construct<binop<mask_match> >     (_val, _1) ]) |
    ("!~" >> bool_op [ at_c<1>(_val) = construct<binop<mask_not_match> > (_val, _1) ]) |
    ("in" >> bool_op [ at_c<1>(_val) = construct<binop<in> >             (_val, _1) ])
    ) >> qi::eps     [ at_c<0>(_val) = type::unknown ])
    ;

还要注意我避免重复代码的倾向，并呈现代码.即使您有一个规定了最大行长的编码标准，它显然更易读、更易于维护并且大大在对齐的列中布局代码的错误更少，像我一样.事实上，你可以争辩说这段代码是元数据"，如果你愿意，它是一个表格，你可以做出一个合理的例外.

Also note my tendency to avoid repeated code, and present the code. Even if you have a coding standard that imposes a maximum line-length, it is clearly more legible, more maintainable and much less error prone to layout the code in aligned columns, like I did. In fact, you could just argue that this piece of code is "meta-data", a table if you will, and you can make a well-reasoned exception.

我想我看到了许多其他代码异味"――或者更积极地说，简化的机会".

I think I see a number of other "code smells" - or, more positively, "opportunities for simplification".

事实上，我过去在 SO 上重构了许多语法，并且通常将代码减少到原始代码的 50%，通常同时添加功能.很遗憾，我现在没有时间找到它们，但也许您可以自己找找.

I have in fact refactored many grammars just like these in the past on SO and usually reduced the code to <50% of the original code, often adding features at the same time. I sadly don't have time to find them right now, but maybe you can have a look for yourself.

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