ceph/src/boost/libs/asio/example/cpp11/spawn/parallel_grep.cpp

   1 //
   2 // parallel_grep.cpp
   3 // ~~~~~~~~~~~~~~~~~
   4 //
   5 // Copyright (c) 2003-2017 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
  26 int 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 }