1 //
2 // parallel_grep.cpp
3 // ~~~~~~~~~~~~~~~~~
4 //
5 // Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
6 //
7 // Distributed under the Boost Software License, Version 1.0. (See accompanying
8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
9 //
10
11 #include <boost/asio/dispatch.hpp>
12 #include <boost/asio/post.hpp>
13 #include <boost/asio/spawn.hpp>
14 #include <boost/asio/strand.hpp>
15 #include <boost/asio/thread_pool.hpp>
16 #include <boost/thread/thread.hpp>
17 #include <boost/bind/bind.hpp>
18 #include <fstream>
19 #include <iostream>
20 #include <string>
21
22 using boost::asio::dispatch;
23 using boost::asio::spawn;
24 using boost::asio::strand;
25 using boost::asio::thread_pool;
26 using boost::asio::yield_context;
27
print_match(std::string input_file,std::string line)28 void print_match(std::string input_file, std::string line)
29 {
30 std::cout << input_file << ':' << line << std::endl;
31 }
32
search_file(std::string search_string,std::string input_file,strand<thread_pool::executor_type> output_strand,yield_context yield)33 void search_file(std::string search_string, std::string input_file,
34 strand<thread_pool::executor_type> output_strand, yield_context yield)
35 {
36 std::ifstream is(input_file.c_str());
37 std::string line;
38 std::size_t line_num = 0;
39 while (std::getline(is, line))
40 {
41 // If we find a match, send a message to the output.
42 if (line.find(search_string) != std::string::npos)
43 {
44 dispatch(output_strand, boost::bind(&print_match, input_file, line));
45 }
46
47 // Every so often we yield control to another coroutine.
48 if (++line_num % 10 == 0)
49 post(yield);
50 }
51 }
52
main(int argc,char * argv[])53 int main(int argc, char* argv[])
54 {
55 try
56 {
57 if (argc < 2)
58 {
59 std::cerr << "Usage: parallel_grep <string> <files...>\n";
60 return 1;
61 }
62
63 // We use a fixed size pool of threads for reading the input files. The
64 // number of threads is automatically determined based on the number of
65 // CPUs available in the system.
66 thread_pool pool;
67
68 // To prevent the output from being garbled, we use a strand to synchronise
69 // printing.
70 strand<thread_pool::executor_type> output_strand(pool.get_executor());
71
72 // Spawn a new coroutine for each file specified on the command line.
73 std::string search_string = argv[1];
74 for (int argn = 2; argn < argc; ++argn)
75 {
76 std::string input_file = argv[argn];
77 spawn(pool, boost::bind(&search_file, search_string,
78 input_file, output_strand, boost::placeholders::_1));
79 }
80
81 // Join the thread pool to wait for all the spawned tasks to complete.
82 pool.join();
83 }
84 catch (std::exception& e)
85 {
86 std::cerr << "Exception: " << e.what() << "\n";
87 }
88
89 return 0;
90 }
91