ceph/src/boost/libs/asio/example/cpp03/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 <boost/thread/thread.hpp>
  17 #include <boost/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
  28 void print_match(std::string input_file, std::string line)
  29 {
  30   std::cout << input_file << ':' << line << std::endl;
  31 }
  32
  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
  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,
  78             search_string, input_file, output_strand, _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 }