Question

1. Run the following code and explain what the code does

• Run this code at least twice and take screenshots
• Explain what the code does
• What is the running result supposed to be
• What caused this issue?

#include <thread>

#include <iostream>

using namespace std;

const unsigned int NTHREADS = 20;

const int ITERS = 10000000;

int counter;

void increment()

{

       for (int i = 0; i < ITERS; i++)

                     counter++;

             

}

void decrement()

{

       for (int i = 0; i<ITERS; i++)

                     counter--;

             

}

int main()

{

       cout << "The counter is " << counter << endl;

      

              thread *threads = new thread[NTHREADS];

      

              for (unsigned int i = 0; i<NTHREADS; i++)

              if (i % 2 == 0)

              threads[i] = thread(increment);

       else

              threads[i] = thread(decrement);

      

              for (unsigned int i = 0; i<NTHREADS; i++)

              threads[i].join();

      

              cout << "The counter is " << counter << endl;

      

              return 0;

}

2. Mutex

A mutex (mutual exlusion) allows us to encapsulate blocks of code that should only be executed in one thread at a time.

Apply mutex to solve the issue in the previous code. Show your revised code and running result.

Answer 1