Array of threads and attempting to pass multiple arguments to function is not working?

Question

I am creating a program with a dynamic number of threads. I have a vector for the threads (thanks, Mohamad); then I attempt to call a function and pass multiple arguments for the thread of execution.

However, my current code gives an error which I assume is due to my odd usage of the 2D array:

In function 'int main()': 102 77 [Error] no matching function for call to 'std::thread::thread(void (&)(float ()[2], float, int, int), float [(((sizetype)(((ssizetype)nodeNumber) + -1)) + 1)][2], float [(((sizetype)(((ssizetype)nodeNumber) + -1)) + 1)], int&, int&)'

102 77 [Note] candidates are: 4 0

133 7 c:\program files (x86)\dev-cpp\mingw64\lib\gcc\x86_64-w64-mingw32\4.8.1\include\c++\thread [Note] template std::thread::thread(_Callable&&, _Args&& ...)

133 7 c:\program files (x86)\dev-cpp\mingw64\lib\gcc\x86_64-w64-mingw32\4.8.1\include\c++\thread [Note] template argument deduction/substitution failed:

102 77 [Note] variable-sized array type 'float (&)[(((sizetype)(((ssizetype)nodeNumber) + -1)) + 1)][2]' is not a valid template argument

4 0 In file included from

128 5 c:\program files (x86)\dev-cpp\mingw64\lib\gcc\x86_64-w64-mingw32\4.8.1\include\c++\thread [Note] std::thread::thread(std::thread&&)

128 5 c:\program files (x86)\dev-cpp\mingw64\lib\gcc\x86_64-w64-mingw32\4.8.1\include\c++\thread [Note] candidate expects 1 argument, 5 provided

122 5 c:\program files (x86)\dev-cpp\mingw64\lib\gcc\x86_64-w64-mingw32\4.8.1\include\c++\thread [Note] std::thread::thread() 122 5 c:\program files (x86)\dev-cpp\mingw64\lib\gcc\x86_64-w64-mingw32\4.8.1\include\c++\thread [Note] candidate expects 0 arguments, 5 provided

Here are some of the chunks of code where I am attempting this:

#include <iostream>
#include <fstream>
#include <string>
#include <thread>
#include <vector>
using namespace std;


void map(float rank_matrix[][2], float adjacency_matrix[], int nodeNumber, int node);

int main()  {
    // setup code, initialization section here

        float adjacency_matrix[nodeNumber][nodeNumber];
        float rank_matrix[nodeNumber][2];

    while(iter < terminate)  {

        vector<thread> threads;

        for(int i = 0; i < nodeNumber; i++)  {
            threads.push_back(std::thread(map, rank_matrix, adjacency_matrix[i], nodeNumber, i);
        }

        for(int i = 0; i < nodeNumber; i++)  {
            threads.join();
        }

        // Flush out the mass for each node (will be updated based on mapper's work.
        for(i = 0; i < nodeNumber; i++)  {
            rank_matrix[i][0] = 0;
        }

        iter++;
        cout << endl;
        cout << endl;
    }

    return 0;
}


// Mapper code for each individual node and computation.
void map(float rank_matrix[][2], float adjacency_matrix[], int nodeNumber,    int node)  {
    for(int i = 0; i < nodeNumber; i++)  {
        if(rank_matrix[node][1] != 0 && adjacency_matrix[i] > 0)
            adjacency_matrix[i] = (rank_matrix[node][0] / rank_matrix[node][1]); 
    }
}

Any suggestions on what I'm doing wrong? Help would be much appreciated! Thanks!

Answer 1

thread myThread[nodeNumber];

This creates a number of default-initialized threads i.e threads that do not represent any thread of execution.

myThread[i](map, rank_matrix, adjacency_matrix[i], nodeNumber, i);

Does not initialize your threads.

I would suggest using a vector of threads like in this example

std::vector<std::thread> threads;

This does not create any actual threads. Just the container to hold them.

Then you can populate it like so:

for(int i = 0; i < nodeNumber; i++)  {
    threads.push_back(std::thread(map, rank_matrix, adjacency_matrix[i], nodeNumber, i);
}