In Linux, the pthread_exit function is used to terminate the calling thread and return a value to the parent thread. It is an important function for managing threads in a multi-threaded application. By using pthread_exit, you can gracefully exit a thread and provide a return value that can be used by the parent thread for further processing.

The pthread_exit function is part of the POSIX threads library, which is the standard threading library for Linux and other Unix-like operating systems. It provides a portable and efficient way to create and manage threads in a multi-threaded application.

Examples:

1. Basic Usage of pthread_exit:

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

void* thread_function(void* arg) {
    int thread_id = *(int*)arg;
    printf("Thread %d is running\n", thread_id);
    pthread_exit(NULL);
}

int main() {
    pthread_t thread;
    int thread_id = 1;
    pthread_create(&thread, NULL, thread_function, &thread_id);
    pthread_join(thread, NULL);
    printf("Thread %d has exited\n", thread_id);
    return 0;
}

In this example, we create a new thread using pthread_create and pass a thread ID as an argument to the thread_function. Inside the thread_function, we print a message indicating that the thread is running and then call pthread_exit to terminate the thread. Finally, in the main function, we wait for the thread to exit using pthread_join and print a message indicating that the thread has exited.

2. Returning a Value from pthread_exit:

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

void* thread_function(void* arg) {
    int thread_id = *(int*)arg;
    printf("Thread %d is running\n", thread_id);
    int* result = malloc(sizeof(int));
    *result = thread_id * 2;
    pthread_exit(result);
}

int main() {
    pthread_t thread;
    int thread_id = 1;
    void* thread_result;
    pthread_create(&thread, NULL, thread_function, &thread_id);
    pthread_join(thread, &thread_result);
    int* result = (int*)thread_result;
    printf("Thread %d has exited with result: %d\n", thread_id, *result);
    free(result);
    return 0;
}

In this example, we modify the thread_function to allocate memory for an integer result and assign it the value of the thread ID multiplied by 2. We then pass the result pointer to pthread_exit, which will be returned to the parent thread. In the main function, we use pthread_join to wait for the thread to exit and retrieve the result using the thread_result pointer. Finally, we print the result and free the memory allocated for it.