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//
// parallel_grep.cpp
// ~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2017 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// 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)
//
#include <boost/asio/dispatch.hpp>
#include <boost/asio/post.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/asio/strand.hpp>
#include <boost/asio/thread_pool.hpp>
#include <boost/thread/thread.hpp>
#include <boost/bind.hpp>
#include <fstream>
#include <iostream>
#include <string>
using boost::asio::dispatch;
using boost::asio::spawn;
using boost::asio::strand;
using boost::asio::thread_pool;
using boost::asio::yield_context;
void print_match(std::string input_file, std::string line)
{
std::cout << input_file << ':' << line << std::endl;
}
void search_file(std::string search_string, std::string input_file,
strand<thread_pool::executor_type> output_strand, yield_context yield)
{
std::ifstream is(input_file.c_str());
std::string line;
std::size_t line_num = 0;
while (std::getline(is, line))
{
// If we find a match, send a message to the output.
if (line.find(search_string) != std::string::npos)
{
dispatch(output_strand, boost::bind(&print_match, input_file, line));
}
// Every so often we yield control to another coroutine.
if (++line_num % 10 == 0)
post(yield);
}
}
int main(int argc, char* argv[])
{
try
{
if (argc < 2)
{
std::cerr << "Usage: parallel_grep <string> <files...>\n";
return 1;
}
// We use a fixed size pool of threads for reading the input files. The
// number of threads is automatically determined based on the number of
// CPUs available in the system.
thread_pool pool;
// To prevent the output from being garbled, we use a strand to synchronise
// printing.
strand<thread_pool::executor_type> output_strand(pool.get_executor());
// Spawn a new coroutine for each file specified on the command line.
std::string search_string = argv[1];
for (int argn = 2; argn < argc; ++argn)
{
std::string input_file = argv[argn];
spawn(pool, boost::bind(&search_file,
search_string, input_file, output_strand, _1));
}
// Join the thread pool to wait for all the spawned tasks to complete.
pool.join();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
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