MultiThreading in C Tutorial - Part3(pthread_exit and pthread_equal)

pthread_exit:
Syntax: void pthread_exit(void *retval);

pthread_exit has two different roles.If it is used in the main thread,it makes it to wait until all the user level threads terminates.If it is used in a thread function it will work like a exit call.

pthread_equal:
Syntax: int pthread_equal(pthread_t t1, pthread_t t2);

pthread_equal is used by the applications to compare two thread values.If two threads are equal, it returns a non zero value,otherwise it returns 0

Example Program:


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


pthread_t tid[2];


void *thread_fn(void *arg)
{

if(pthread_equal(tid[0], pthread_self()))
printf("Thread 0 in execution\n");
else
printf("Thread 1 in execution\n");
pthread_exit(NULL);
}

int main()
{

int i;
int ret;
for (i = 0;i < 2;i++) {
ret = pthread_create(&tid[i], NULL, thread_fn, NULL);
if (!ret)
printf("Thread[%d] created Successfully\n",i+1);
else
printf("Thread[%d] not created\n",i+1);

}
pthread_exit(NULL);
printf("After thread execution completed\n");
return 0;
}

Compile it with -lpthread flag to gcc

What is the difference between pthread_exit and pthread_join? Which we have to use at what position?

pthread_exit() will terminate the thread that is called.If you call it from your main thread,the main thread is terminated and your spawned threads continue execution.So anything you write after pthread_exit in the main thread will not be execcuted.This will be useful in a scenario in which your main thread has to just spawn threads.

pthread_join() will suspend the execution of the currently running thread until the particular thread you want is terminated,after that it resumes its execution.Useful where you have to wait until a particular thread completes its execution

If you write exit or return in your main thread , the whole process is terminated,but if you write pthread-exit in your main thread only that particular thread terminates and remaining threads continue their execution.