C++ thread library exception

Question

I have some issues with C++ thread library. I have adapted my old code for optimization of a new problem and suddenly an uncaught exception is thrown (During runtime). Some threads are joined successfully, but there's always at least one throwing an exception. Only thing which I changed in the code, was data representation. They were earlier held in 2D arrays and now I am using 1D vectors. Here is the exact runtime error I receive:

libc++abi.dylib: terminating with uncaught exception of type std::__1::system_error: thread::join failed: Invalid argument

Below I provide the minimal reproducible example, throwing the exact same exception like in the case of the complete code.

Here is the main function:

#include <iostream>
#include <thread>
#include <vector>

void reforming(const int, const std::vector<int>&, const std::vector<double>&, const std::vector<double>&);

int main() {
    int i, k;
    int spec_max = 10;
    int seg_max = 4;
    size_t pop_size = spec_max * seg_max;
    std::vector<int> seg(pop_size);
    std::vector<double> por(pop_size);
    std::vector<double> por_s(pop_size);

    for(i = 0; i < pop_size; i++){
        if(i % 2 == 0){
            seg[i] = 1;
            por[i] = 0.5;
            por_s[i] = 0.0015;
        } else {
            seg[i] = 0;
            por[i] = 0.7;
            por_s[i] = 0.002;
        }
    }

    std::vector<std::thread> Ref(spec_max);
    for(k = 0; k < spec_max; k++){
        Ref.emplace_back(reforming, k, seg, por, por_s);
    }

    for(auto &X : Ref){
        X.join();
    }
    return 0;
}

and the "reforming" function:

#include <iostream>
#include <vector>

void reforming(const int m, const std::vector<int>& cat_check, const std::vector<double>& por,
        const std::vector<double>& por_s){

        std::cout << m << " Hello from the thread\n";
}

I am using the CLion software on MacOS Catalina and currently have no other OS available to test the code.

Answer 1

The following code:

std::vector<std::thread> Ref(spec_max);
for(k = 0; k < spec_max; k++){
    Ref.emplace_back(reforming, k, seg, por, por_s);
}

creates 2 * spec_max threads, the first spec_max threads are default-initialized. Trying to join a default-initialized thread throws std::system_error.

A fix:

std::vector<std::thread> Ref;
Ref.reserve(spec_max);
for(k = 0; k < spec_max; k++){
    Ref.emplace_back(reforming, k, seg, por, por_s);
}