Creating and Managing Threads

In multithreading, we create multiple threads to execute tasks concurrently.

In this lesson, you will learn:

• How to create multiple threads in C.
• How to wait for threads to finish execution.
• How to pass arguments to threads.

We use pthread_create() to create multiple threads.

Syntax:

pthread_create(&thread, NULL, function, argument);

Each thread runs independently but shares memory with other threads.

This program creates multiple threads that run concurrently.

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

void *printMessage(void *arg) {
    printf("Thread %d: Hello from thread!\n", *(int*)arg);
    return NULL;
}

int main() {
    pthread_t threads[3];
    int thread_ids[3] = {1, 2, 3};

    for (int i = 0; i < 3; i++) {
        pthread_create(&threads[i], NULL, printMessage, &thread_ids[i]);
    }

    for (int i = 0; i < 3; i++) {
        pthread_join(threads[i], NULL);
    }
    return 0;
}

Use pthread_join() to wait for a thread to complete.

Syntax:

pthread_join(thread, NULL);

Without pthread_join(), the main thread may exit before other threads finish.

Arguments can be passed to a thread function using a pointer.

Example:

pthread_create(&thread, NULL, function, (void*)&value);

The thread function casts the argument back to its original type.

This program demonstrates how to pass arguments to a thread function.

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

void *printNumber(void *arg) {
    int num = *(int*)arg;
    printf("Thread received number: %d\n", num);
    return NULL;
}

int main() {
    pthread_t thread;
    int value = 10;
    pthread_create(&thread, NULL, printNumber, &value);
    pthread_join(thread, NULL);
    return 0;
}

Use pthread_exit() to terminate a thread explicitly.

Example:

pthread_exit(NULL);

The main function should also call pthread_exit() if needed.

To manage threads efficiently:

• Always use pthread_join() to avoid premature termination.
• Pass arguments using pointers to avoid data corruption.
• Minimize shared resource conflicts.

In this lesson, you learned:

• How to create multiple threads using pthread_create().
• How to wait for threads using pthread_join().
• How to pass arguments to threads.
• How to terminate a thread safely.

Next, we will explore synchronization and race conditions in multithreading!