《C++并发编程实战》随笔
#include <iostream>
#include <algorithm>
#include <numeric>
#include <thread>
#include <vector>
#include <functional>
template<class Iterator,class T>
struct accumulate_block {
void operator()(Iterator first,Iterator last,T &result) {
result = std::accumulate(first,last,result);
}
};
template<class Iterator,class T>
T parallel_accumulate(Iterator first,Iterator last,T init) {
unsigned long const length = std::distance(first,last);
if(!length)return init;
// 假设最大线程为25
unsigned long const min_pre_thread = 25;
// 按照元素长度来分配线程,以免元素过少分配过量的线程
unsigned long const max_threads =
(length + min_pre_thread) / min_pre_thread;
unsigned long const hardware_threads =
std::thread::hardware_concurrency();
//取本机可使用的最小执行线程
unsigned long const num_threads =
std::min(hardware_threads != 0 ? hardware_threads : 2,max_threads);
//计算每个线程需计算的量
unsigned long const block_size = length / num_threads;
std::vector<T> result(num_threads);
std::vector<std::thread> threads(num_threads - 1);
Iterator block_start = first;
for(unsigned long i = 0;i < num_threads - 1;i ++) {
Iterator block_end = block_start;
std::advance(block_end,block_size);
threads[i] = std::thread {
accumulate_block<Iterator,T>(),
block_start,
block_end,
std::ref(result[i])
};
block_start = block_end;
};
accumulate_block<Iterator,T>()(
block_start,last,result[num_threads - 1]
);
for(auto &&th:threads)
th.join();
return std::accumulate(result.begin(),result.end(),init);
}
int main() {
std::vector<int> ans {1,2,3,4,5};
auto res = parallel_accumulate(ans.begin(),ans.end(),0);
std::cout << res << "\n";
return 0;
}
原文链接: https://www.cnblogs.com/xianning7/p/14771459.html
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