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/* Boost.Flyweight example of parallel tokenization.
*
* Copyright 2024 Joaquin M Lopez Munoz.
* Distributed under the Boost Software License, Version 1.0.
* (See accompanying file LICENSE_1_0.txt or copy at
* http://www.boost.org/LICENSE_1_0.txt)
*
* See http://www.boost.org/libs/flyweight for library home page.
*/
#include <boost/flyweight.hpp>
#include <boost/flyweight/concurrent_factory.hpp>
#include <boost/flyweight/no_locking.hpp>
#include <boost/flyweight/no_tracking.hpp>
#include <chrono>
#include <cstdlib>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <string>
#include <thread>
#include <vector>
/* Handcrafted tokenizer for sequences of alphabetic characters */
inline bool match(char ch)
{
return (ch>='a' && ch<='z') || (ch>='A' && ch<='Z');
}
template<typename ForwardIterator,typename F>
void tokenize(ForwardIterator first,ForwardIterator last,F f)
{
goto start;
for(;;)
{
for(;;){
++first;
start:
if(first==last)return;
if(match(*first))break;
}
auto begin_word=first;
for(;;){
if(++first==last||!match(*first)){
f(begin_word,first);
if(first==last)return;
else break;
}
}
}
}
/* Tokenize a string into words in parallel and store the results into a
* std::vector<String>, String being std::string or a flyweight type.
*/
template<typename String>
void parse(const std::string& in,const char* type_name,std::size_t num_threads)
{
using namespace std::chrono;
using string_iterator=std::string::const_iterator;
auto t1=steady_clock::now();
/* Divide input in num_threads chunks, taking care that boundaries are not
* placed in the middle of a token.
*/
std::vector<string_iterator> boundaries(num_threads+1);
boundaries[0]=in.begin();
for(std::size_t i=0;i<num_threads;++i){
auto& it=boundaries[i+1];
it=boundaries[i]+(in.end()-boundaries[i])/(num_threads-i);
while(it!=in.end()&&match(*it))++it;
}
/* do a first pass to precalculate # of words produced by each thread */
std::vector<std::thread> threads(num_threads);
std::vector<std::size_t> partial_num_words(num_threads);
for(std::size_t i=0;i<num_threads;++i){
threads[i]=std::thread([&,i]{
std::size_t s=0;
tokenize(
boundaries[i],boundaries[i+1],
[&](string_iterator,string_iterator){++s;});
partial_num_words[i]=s;
});
}
std::size_t num_words=0;
std::vector<std::size_t> thread_output_starts(num_threads);
for(std::size_t i=0;i<num_threads;++i){
threads[i].join();
thread_output_starts[i]=num_words;
num_words+=partial_num_words[i];
}
/* do a second pass, this time populating the result vector */
std::vector<String> words(num_words,String());
for(std::size_t i=0;i<num_threads;++i){
threads[i]=std::thread([&,i]{
auto out=words.begin()+thread_output_starts[i];
tokenize(
boundaries[i],boundaries[i+1],
[&](string_iterator first,string_iterator last){
*out++=String(first,last);
});
});
}
for(std::size_t i=0;i<num_threads;++i){threads[i].join();}
auto t2=steady_clock::now();
std::cout
<<std::setw(20)<<type_name<<", "<<num_threads<<" thread(s): "
<<num_words<<" words, "
<<std::setw(9)<<duration_cast<duration<double>>(t2-t1).count()<< " s\n";
}
/* accept a file and parse it with std::string and various flyweight types */
int main(int argc, char** argv)
{
using namespace boost::flyweights;
using regular_flyweight=flyweight<std::string>;
using concurrent_flyweight=flyweight<
std::string,
concurrent_factory<>,
no_locking,
no_tracking
>;
if(argc<2){
std::cout<<"specify a file\n";
std::exit(EXIT_FAILURE);
}
std::ifstream is(argv[1]);
if(!is)
{
std::cout<<"can't open "<<argv[1]<<"\n";
std::exit(EXIT_FAILURE);
}
std::string in(
std::istreambuf_iterator<char>(is),std::istreambuf_iterator<char>{});
parse<std::string>(in,"std::string",1);
parse<std::string>(in,"std::string",8);
parse<regular_flyweight>(in,"regular flyweight",1);
parse<regular_flyweight>(in,"regular flyweight",8);
parse<concurrent_flyweight>(in,"concurrent flyweight",1);
parse<concurrent_flyweight>(in,"concurrent flyweight",8);
}
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