Close a thread when done with it

Question

How do you close a thread, when you done? like making sure nothing is open anymore or runing?

so far i know how to open it, but .. not how to close it right

int  iret1; 
pthread_t thread1;
char *message1;

void *multithreading1( void *ptr ) {
    while (1) {
        // Our function here
    }   
}

int main (int argc, char * const argv[]) {
    if( (iret1=pthread_create( &thread1, NULL, multithreading1, (void*) message1)) )
    {
        printf("Thread creation failed: %d\n", iret1);
    }
    return 0;
}

Answer 1

"How do you close a thread, when you done?"
Either by just simple returning from that function or calling pthread_exit function.

Note that calling return also causes the stack to be unwound and variables declared within start routine to be destroyed, thus it's more preferable than pthread_exit function:

An implicit call to pthread_exit() is made when a thread other than the thread in
which main() was first invoked returns from the start routine that was used to
create it. The function's return value shall serve as the thread's exit status.

For more information also have a look at: return() versus pthread_exit() in pthread start functions

"making sure nothing is open anymore or runing"
Instead of making sure whether your thread is still running, you should wait for its termination by using pthread_join function.

Here's an example:

void *routine(void *ptr) {
    int* arg = (int*) ptr; // in C, explicit type cast is redundant
    printf("changing %d to 7\n", *arg);
    *arg = 7;
    return ptr;
}

int main(int argc, char * const argv[]) {
    pthread_t thread1;
    int arg = 3;
    pthread_create(&thread1, NULL, routine, (void*) &arg);

    int* retval;
    pthread_join(thread1, (void**) &retval);
    printf("thread1 returned %d\n", *retval);
    return 0;
}

output

changing 3 to 7
thread1 returned 7