Mandatory task 3 ING2504 Fall 2025

Part 1: Basic locking

Compile and execute the following C-program. Note this will run forever or until you stop it by pressing CTRL-C (this sends a SIGINT-signal to the process which will make the operating system terminate the process).

#include <stdio.h>
#include <pthread.h>
#include <string.h>

typedef struct {
    char name[100];
    int age;
} Person;

Person person;

void *thread1_func(void *arg) {
    int counter=0;
    int noerror=1;

    while(1) {
        counter++;
        strcpy(person.name, "Alice");
        person.age = 30;

        if (strcmp(person.name, "Alice") != 0 || person.age != 30) {
            printf("Thread 1: Alice is not 30! she is %d\n", person.age);
            noerror=0;
        }
        if (noerror == 1 && (counter % 1000000 == 0)) {
            printf("Hey you rock! Alice's OK!\n");
        }
    }

    return NULL;
}

void *thread2_func(void *arg) {
    int counter=0;
    int noerror=1;

    while(1) {
        counter++;
        strcpy(person.name, "Bob");
        person.age = 25;

        if (strcmp(person.name, "Bob") != 0 || person.age != 25) {
            printf("Thread 2: Bob is not 25! he is %d\n", person.age);
            noerror=0;
        }
        if (noerror == 1 && (counter % 1000000 == 0)) {
            printf("Hey you rock! Bob's OK!\n");
            }
    }

    return NULL;
}

int main() {
    pthread_t thread1, thread2;

    pthread_create(&thread1, NULL, thread1_func, NULL);
    pthread_create(&thread2, NULL, thread2_func, NULL);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    return 0;
}

This will generate output like this:

Thread 2: Bob is not 25! he is 30
Thread 2: Bob is not 25! he is 30
Thread 1: Alice is not 30! she is 25
Thread 1: Alice is not 30! she is 25
Thread 1: Alice is not 30! she is 25
Thread 2: Bob is not 25! he is 30
Thread 1: Alice is not 30! she is 25

Add locks to the two threads in such a way that the output instead will be:

Hey you rock! Alice's OK!
Hey you rock! Bob's OK!
Hey you rock! Bob's OK!
Hey you rock! Alice's OK!
Hey you rock! Bob's OK!

• Make sure to keep the parallelism: do not insert locks in a way that will cause only one thread to execute.
• Place the locks only around the statements where you really need locks.

Part 2: Reader-Writer

In the compendia chapter 8, do the exercise number 5 (5. (KEY PROBLEM) In chapter 31, Homework (code), let us do the following...). Note: you only have to demonstrate part (d) to your teaching assistant.