ceph/src/boost/libs/thread/example/parallel_accumulate.cpp

   1 // Copyright (C) 2014 Vicente Botet
   2 //
   3 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   5
   6 #include <boost/config.hpp>
   7
   8 #define BOOST_THREAD_VERSION 4
   9 #define BOOST_THREAD_PROVIDES_EXECUTORS
  10 #define BOOST_THREAD_USES_LOG_THREAD_ID
  11 #define BOOST_THREAD_QUEUE_DEPRECATE_OLD
  12 #if ! defined  BOOST_NO_CXX11_DECLTYPE
  13 #define BOOST_RESULT_OF_USE_DECLTYPE
  14 #endif
  15
  16 #include <boost/thread/executors/basic_thread_pool.hpp>
  17 #include <boost/thread/future.hpp>
  18
  19 #include <numeric>
  20 #include <algorithm>
  21 #include <functional>
  22 #include <iostream>
  23 #include <vector>
  24
  25 #if defined(BOOST_THREAD_PROVIDES_VARIADIC_THREAD)
  26
  27 template<typename Iterator,typename T>
  28 struct accumulate_block
  29 {
  30     //typedef T result_type;
  31     T operator()(Iterator first,Iterator last)
  32     {
  33         return std::accumulate(first,last,T());
  34     }
  35 };
  36
  37 template<typename Iterator,typename T>
  38 T parallel_accumulate(Iterator first,Iterator last,T init)
  39 {
  40     unsigned long const length=static_cast<unsigned long>(std::distance(first,last));
  41
  42     if(!length)
  43         return init;
  44
  45     unsigned long const block_size=25;
  46     unsigned long const num_blocks=(length+block_size-1)/block_size;
  47
  48     boost::csbl::vector<boost::future<T> > futures(num_blocks-1);
  49     boost::basic_thread_pool pool;
  50
  51     Iterator block_start=first;
  52     for(unsigned long i=0;i<(num_blocks-1);++i)
  53     {
  54         Iterator block_end=block_start;
  55         std::advance(block_end,block_size);
  56         futures[i]=boost::async(pool, accumulate_block<Iterator,T>(), block_start, block_end);
  57         block_start=block_end;
  58     }
  59     T last_result=accumulate_block<Iterator,T>()(block_start,last);
  60     T result=init;
  61     for(unsigned long i=0;i<(num_blocks-1);++i)
  62     {
  63         result+=futures[i].get();
  64     }
  65     result += last_result;
  66     return result;
  67 }
  68
  69
  70 int main()
  71 {
  72   try
  73   {
  74     const int s = 1001;
  75     std::vector<int> vec;
  76     vec.reserve(s);
  77     for (int i=0; i<s;++i)
  78       vec.push_back(1);
  79     int r = parallel_accumulate(vec.begin(), vec.end(),0);
  80     std::cout << r << std::endl;
  81
  82   }
  83   catch (std::exception& ex)
  84   {
  85     std::cout << "ERROR= " << ex.what() << "" << std::endl;
  86     return 1;
  87   }
  88   catch (...)
  89   {
  90     std::cout << " ERROR= exception thrown" << std::endl;
  91     return 2;
  92   }
  93   return 0;
  94 }
  95
  96 #else
  97 ///#warning "This compiler doesn't supports variadics"
  98 int main()
  99 {
 100   return 0;
 101 }
 102 #endif