1. Objectives

Understand the race condition

Know the multithreading programming

Understand how to use mutex to solve the race condition

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

Run this code at least twice and take screenshots (20 points)

Explain what the code does (20 points)

What is the running result supposed to be (20 points)

What caused this issue? (10 points)

#include

#include

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

counter--;

}

int main()

{

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

thread *threads = new thread[NTHREADS];

or (unsigned int i = 0; i

if (i % 2 == 0)

threads[i] = thread(increment);

else

threads[i] = thread(decrement);

for (unsigned int i = 0; i

threads[i].join();

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

return 0;

}

3. 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 previous code. Show your revised code (20 points) and running result (10 points).