1 // 2 // parallel_grep.cpp 3 // ~~~~~~~~~~~~~~~~~ 4 // 5 // Copyright (c) 2003-2020 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 <fstream> 17 #include <iostream> 18 #include <string> 19 20 using boost::asio::dispatch; 21 using boost::asio::spawn; 22 using boost::asio::strand; 23 using boost::asio::thread_pool; 24 using boost::asio::yield_context; 25 main(int argc,char * argv[])26int main(int argc, char* argv[]) 27 { 28 try 29 { 30 if (argc < 2) 31 { 32 std::cerr << "Usage: parallel_grep <string> <files...>\n"; 33 return 1; 34 } 35 36 // We use a fixed size pool of threads for reading the input files. The 37 // number of threads is automatically determined based on the number of 38 // CPUs available in the system. 39 thread_pool pool; 40 41 // To prevent the output from being garbled, we use a strand to synchronise 42 // printing. 43 strand<thread_pool::executor_type> output_strand(pool.get_executor()); 44 45 // Spawn a new coroutine for each file specified on the command line. 46 std::string search_string = argv[1]; 47 for (int argn = 2; argn < argc; ++argn) 48 { 49 std::string input_file = argv[argn]; 50 spawn(pool, 51 [=](yield_context yield) 52 { 53 std::ifstream is(input_file.c_str()); 54 std::string line; 55 std::size_t line_num = 0; 56 while (std::getline(is, line)) 57 { 58 // If we find a match, send a message to the output. 59 if (line.find(search_string) != std::string::npos) 60 { 61 dispatch(output_strand, 62 [=] 63 { 64 std::cout << input_file << ':' << line << std::endl; 65 }); 66 } 67 68 // Every so often we yield control to another coroutine. 69 if (++line_num % 10 == 0) 70 post(yield); 71 } 72 }); 73 } 74 75 // Join the thread pool to wait for all the spawned tasks to complete. 76 pool.join(); 77 } 78 catch (std::exception& e) 79 { 80 std::cerr << "Exception: " << e.what() << "\n"; 81 } 82 83 return 0; 84 } 85