Pthread create as detached

Question

I have a problem creating a thread as detached. Here's the code I wrote:

void* testFunction() {

    pthread_attr_t attr;
    int chk,rc;

pthread_attr_init(&attr);
printf("thread_attr_init: %d\n",rc);

pthread_attr_getdetachstate(&attr, &chk);
printf("thread_attr_getdetachedstate: %d\n",rc);

if(chk == PTHREAD_CREATE_DETACHED ) 
    printf("Detached\n");
else if (chk == PTHREAD_CREATE_JOINABLE) 
    printf("Joinable\n");

return NULL;
}


int main (int argc, const char * argv[]) {

pthread_t thread1;
pthread_attr_t attr;

int rc;

rc = pthread_attr_init(&attr);

printf("attr_init: %d\n",rc);
rc = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
printf("attr_setdetachedstate: %d\n",rc);

rc = pthread_create(&thread1, &attr, testFunction, NULL);
printf("attr_create: %d\n",rc);

sleep(4);
pthread_cancel(thread1);

return 0;
}

The problem is that testFunction() always print "Joinable". Can anyone tell me where I'm getting wrong?

Answer 1

Your testFunction is not examining anything about the current thread, rather just the initially-detached flag of a completely new attribute object you just created. Moreover, it is completely impossible, in the POSIX threads API, to recover the attributes a thread was created with or determine if a thread is detached or not. You simply have to trust that the implementation behaves as required, just like you have to trust that, if malloc(100) returns a non-null pointer, it points to a location at which you can store at least 100 bytes. This is the nature of C.