__gnu_parallel::sort()对空间是否有要求

 目的：在使用__gnu_parallel::sort()时，发现改方法对空间好像有要求，所以测试__gnu_parallel::sort()的空间

需求。

方法： 在4G内存的机器上运行一个大的数据，然后调用__gnu_parallel::sort()排序，看是否能正常运行。

结果：该方法确实需要两倍的排序空间

#include <iostream>
#include <vector>
#include <stdio.h>
#include<stdlib.h>
#include<string>
///STL parallel sort Library
#include <parallel/algorithm>

using uint32 = unsigned int;
using uint64 = unsigned long long int;
using uint8 = unsigned char;




int main()
{
    uint32 s_len = 3*1014*1024*1024;

    uint8 * buf = new uint8[s_len];

    std::cout << "s_len = " << s_len / 1024 / 1024 / 1024 << "G.\n";

    for(uint32 i = 0; i < s_len; ++i){

        buf[i] = rand()%256;
    }

    std::cout << "buffer is ready.\n";

    std::cout << "start to sort.\n";

    __gnu_parallel::sort(buf,buf+s_len,std::less<uint8>());

    std::cout << "sort closed.\n";

    std::cout << "close.\n";

    return 0;
}