[Modern C++]現代C++中的異步操作
作者：佚名
如果在輸出中間信息的時候不先現在字符串里輸出會很亂，因為同一行cout輸出不同項的操作不是原子的，中間可能會轉到其他線程去。
背景
老實說，C++11中對異步的支持不必Python和JavaScript弱。
實現(代碼)
- #include <iostream>
- #include <vector>
- #include <algorithm>
- #include <future>
- template <typename RAIter>
- int parallel_sum(RAIter front, RAIter beg, RAIter end)
- {
- auto len = end - beg;
- if (len < 1000)
- {
- char out[50];
- sprintf(out, "Calculate from %d to %d\n", beg - front, end - front);
- std::cout << out;
- return std::accumulate(beg, end, 0);
- }
- RAIter mid = beg + len / 2;
- auto handle_right = std::async(std::launch::async,
- parallel_sum<RAIter>, front, mid, end);
- auto handle_left = std::async(std::launch::async,
- parallel_sum<RAIter>, front, beg, mid);
- return handle_left.get() + handle_right.get();
- }
- int main()
- {
- std::vector<int> v(20000, 1);
- std::cout << "The sum is " << parallel_sum(v.begin(), v.begin(), v.end()) << '\n';
- }
輸出
可能一
- Calculate from 8125 to 8750
- Calculate from 18125 to 18750
- Calculate from 10625 to 11250
- Calculate from 2500 to 3125
- Calculate from 13750 to 14375
- Calculate from 5000 to 5625
- Calculate from 1250 to 1875
- Calculate from 3750 to 4375
- Calculate from 16250 to 16875
- Calculate from 17500 to 18125
- Calculate from 10000 to 10625
- Calculate from 625 to 1250
- Calculate from 18750 to 19375
- Calculate from 15625 to 16250
- Calculate from 3125 to 3750
- Calculate from 12500 to 13125
- The sum is 20000
可能二
- Calculate from 1875 to 2500
- Calculate from 3750 to 4375
- Calculate from 8750 to 9375
- Calculate from 7500 to 8125
- Calculate from 15000 to 15625
- Calculate from 10000 to 10625
- Calculate from 1250 to 1875
- Calculate from 6875 to 7500
- Calculate from 0 to 625
- Calculate from 3125 to 3750
- Calculate from 5625 to 6250
- Calculate from 5000 to 5625
- Calculate from 6250 to 6875
- Calculate from 2500 to 3125
- The sum is 20000
可能.........
注意
如果在輸出中間信息的時候不先現在字符串里輸出會很亂，因為同一行cout輸出不同項的操作不是原子的，中間可能會轉到其他線程去。
責任編輯：武曉燕
來源：
segmentfault
