C++11 线程：将向量传递给线程函数时出错

Question

作为一个更大项目的一部分，我正在研究多线程中值函数。我几乎没有 C++ 经验。下面的中值函数应采用 3 维 int 向量的向量，并返回一个 3 维 int 向量，其中每个条目是输入向量中该索引中所有条目的中值。所以如果输入是,,>，则返回。此代码将用于实现用于实时视频的中值模糊，因此需要多线程。

#include <thread>
#include <iostream>
#include <mutex>
#include <vector>
#include <algorithm>
#include "median.h"

// mutex to protect bgrPixel (possibly not needed)
std::mutex mtx;


std::vector<int> median(const std::vector<std::vector<int> >& input)
{
    std::vector<int> bgrPixel;              // Vector to store median BGR value
    std::thread first(thread_function, bgrPixel, input, 0); // thread for each colour channel
    std::thread second(thread_function, bgrPixel, input, 1);
    std::thread third(thread_function, bgrPixel, input, 2);
    first.join();
    second.join();
    third.join(); 
    return bgrPixel;
}

void thread_function(std::vector<int>& bgrPixel, const std::vector<std::vector<int> >&                 input1, int channel)
{

    std::vector<int> input = input1[channel];  // copy the colour channel
    std::sort(input.begin(), input.end());
    int size = input.size();
    if (size %2 == 0)   // get the median
    {
        mtx.lock();
        bgrPixel[channel] = (input[size/2] + input[size/2 + 1])/2;
        mtx.unlock();
    } else
    {
        mtx.lock();
        bgrPixel[channel] = input[(size-1)/2];
        mtx.unlock();
    }
}

我遇到的问题是，在编译时，g++（还有 clang）给出了一个相当难以理解的错误：

 g++ -std=c++11 -pthread -o median median.cpp

 In file included from /usr/include/c++/4.8.2/thread:39:0,
                  from median.cpp:1:
 /usr/include/c++/4.8.2/functional: In instantiation of ‘struct std::_Bind_simple<void           (*(std::vector<int>, std::vector<std::vector<int> >, int))(std::vector<int>&, const      std::vector<std::vector<int> >&, int)>’:
 /usr/include/c++/4.8.2/thread:137:47:   required from ‘std::thread::thread(_Callable&&,           _Args&& ...) [with _Callable = void (&)(std::vector<int>&, const      std::vector<std::vector<int> >&, int); _Args = {std::vector<int, std::allocator<int> >&,      const std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int,      std::allocator<int> > > >&, int}]’
 median.cpp:15:58:   required from here
 /usr/include/c++/4.8.2/functional:1697:61: error: no type named ‘type’ in ‘class                std::result_of<void (*(std::vector<int>, std::vector<std::vector<int> >, int))     (std::vector<int>&, const std::vector<std::vector<int> >&, int)>’
        typedef typename result_of<_Callable(_Args...)>::type result_type;
                                                         ^
 /usr/include/c++/4.8.2/functional:1727:9: error: no type named ‘type’ in ‘class      std::result_of<void (*(std::vector<int>, std::vector<std::vector<int> >, int))     (std::vector<int>&, const std::vector<std::vector<int> >&, int)>’
          _M_invoke(_Index_tuple<_Indices...>)
          ^

我发现了类似的错误消息c++11 Thread class how to use a class member function，但它并没有专门处理我的问题。 任何帮助将不胜感激，我完全希望这是因为我不知道我在做什么：P

编辑：thread_function 和 median 的原型包含在头文件 median.h 中。

Answer 1

替换

std::thread first(thread_function, bgrPixel, input, 0);

由

std::thread first(thread_function, std::ref(bgrPixel), std::ref(input), 0);

现场示例：http://coliru.stacked-crooked.com/a/630775aafc3d4642