c++ - Double free or corruption (out) on return

I'm doing an assignment that involves calculating pi with threads. I've done this using mutex and it works fine, but I would like to get this version working as well. Here is my code.

#include 
#include 
#include 
#include 
#include 

using namespace std;

typedef struct{

    int iterations;     //How many iterations this thread is going to do
    int offset;         //The offset multiplier for the calculations (Makes sure each thread calculates a different part of the formula)
}threadParameterList;

vector partialSumList;

void* pi_calc(void* param){
    threadParameterList* _param = static_cast(param);
    double k = 1.0;
    for(int i = _param->iterations * _param->offset + 1; i < _param->iterations * (_param->offset + 1); ++i){

        partialSumList[_param->offset] += (double)k*(4.0/((2.0*i)*(2.0*i+1.0)*(2.0*i+2.0))); 
        k *= -1.0;
    }
    pthread_exit(0);
}

int main(int argc, char* argv[]){

    //Error checking
    if(argc != 3){

        cout << "error: two parameters required [iterations][threadcount]" << endl;
        return -1;
    }
    if(atoi(argv[1]) <= 0 || atoi(argv[2]) <= 0){
        cout << "error: invalid parameter supplied - parameters must be > 0." << endl;
        return -1;
    }

    partialSumList.resize(atoi(argv[2]));


    vector           threadList    (atoi(argv[2]));
    vector parameterList (atoi(argv[2]));

    int iterations  = atoi(argv[1]),
        threadCount = atoi(argv[2]);

    //Calculate workload for each thread
    if(iterations % threadCount == 0){  //Threads divide evenly
        for(int i = 0; i < threadCount; ++i){
            parameterList[i].iterations = iterations/threadCount;

            parameterList[i].offset = i;
            pthread_create(&threadList[i], NULL, pi_calc, ¶meterList[i]);
        }
        void* status;
        for(int i = 0; i < threadCount; ++i){
            pthread_join(threadList[i], &status);
        }

    }
    else{                               //Threads do not divide evenly

        for(int i = 0; i < threadCount - 1; ++i){
            parameterList[i].iterations = iterations/threadCount;
            parameterList[i].offset = i;
            pthread_create(&threadList[i], NULL, pi_calc, ¶meterList[i]);
        }
        //Add the remainder to the last thread
        parameterList[threadCount].iterations = (iterations % threadCount) + (iterations / threadCount);
        parameterList[threadCount].offset = threadCount - 1;
        pthread_create(&threadList[threadCount], NULL, pi_calc, ¶meterList[threadCount]);
        void* status;

        for(int i = 0; i < threadCount-1; ++i){
            pthread_join(threadList[i], &status);
            cout << status << endl;
        }
    }

    //calculate pi
    double pi = 3.0;
    for(int i = 0; i < partialSumList.size(); ++i){
        pi += partialSumList[i];

    }

    cout << "Value of pi: " << setw(15) << setprecision(15) << pi << endl;

    return 0;
}

The code works fine in most cases. There are certain combinations of parameters that cause me to get a double free or corruption error on return 0. For example, if I use the parameters 100 and 10 the program creates 10 threads and does 10 iterations of the formula on each thread, works fine. If I use the parameters 10 and 4 the program creates 4 threads that do 2 iterations on 3 threads and 4 on the 4th thread, works fine. However, if I use 5 and 3, the program will correctly calculate the value and even print it out, but I get the error immediately after. This also happens for 17 and 3, and 10 and 3. I tried 15 and 7, but then I get a munmap_chunk(): invalid pointer error when the threads are trying to be joined - although i think that's something for another question.

If I had to guess, it has something to do with pthread_exit deallocating memory and then the same memory trying to be deallocated again on return, since I'm passing the parameter struct as a pointer. I tried a few different things like creating a local copy and defining parameterList as a vector of pointers, but it didn't solve anything. I've also tried eraseing and clearing the vector before return but that didn't help either.

Answer

I see this issue:

You are writing beyond the vector's bounds:

    vector parameterList (atoi(argv[2]));
    //...
    int        threadCount = atoi(argv[2]);
    //...

    parameterList[threadCount].iterations = (iterations % threadCount) + (iterations / threadCount);
    parameterList[threadCount].offset = threadCount - 1;

Accessing parameterList[threadCount] is out of bounds.

I don't see in the code where threadCount is adjusted, so it remains the same value throughout that snippet.

Tip: If the goal is to access the last item in a container, use vector::back(). It works all the time for non-empty vectors.

    parameterList.back().iterations = (iterations % threadCount) + (iterations / threadCount);
    parameterList.back().offset = threadCount - 1;