Output for simple program using pthread - c++

Question

void cleanupHandler(void *arg) {
printf("In the cleanup handler\n");
}
void *Thread(void *string) {
int i;
int o_state;
int o_type;
pthread_cleanup_push(cleanupHandler, NULL);
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &o_state);
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &o_type);
puts("1 Hello World");
pthread_setcancelstate(o_state, &o_state);
puts("2 Hello World");
pthread_cleanup_pop(0);
pthread_exit(NULL);
}
int main() {
pthread_t th;
int rc;
rc = pthread_create(&th, NULL, Thread, NULL);
pthread_cancel(th);
pthread_exit(NULL);
}
I was wondering what the output of this code would be and in what order they would happen. Yes, this is a practice test question for an exam I have in 6 hours. Any help would be greatly appreciated. There are no office hours today as all of the TA's for my college are busy with their own finals.
Thanks

Answer 1

Here are the man pages you need to understand the problem they will be putting on the exam (which most certainly won't be the exact problem above.) So you need to understand what each of those functions does.
http://man7.org/linux/man-pages/man3/pthread_cleanup_push.3.html
http://man7.org/linux/man-pages/man3/pthread_setcanceltype.3.html,
http://man7.org/linux/man-pages/man3/pthread_cancel.3.html
http://man7.org/linux/man-pages/man3/pthread_exit.3.html
cleanup_push pushs a handler on a stack of functions that will be called if the calling thread is cancelled or exits.
setcancelstate temporarily locks out cancels (so that you can call setcanceltype atomically without weirdness happening.)
setcanceltype allows/disallows asynchronous cancellation notification.
cancel actually attempts to cancel the other thread.
exit exits from the calling thread.
You also need to understand whether pthread_setcancelstate is a cancellation point. You will find that information either on the above man pages or on http://man7.org/linux/man-pages/man7/pthreads.7.html.
In this question (and presumably the similar one that will be on your exam), you need to enumerate all possible interleavings of calls to these functions between the two threads.

Answer 2

1 Hello World
2 Hello World
Why not just compile it and run it? This version compiles and runs.
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void cleanupHandler(void *arg) {
printf("In the cleanup handler\n");
}
void* Thread(void *string) {
int i;
int o_state;
int o_type;
sleep(1);
pthread_cleanup_push(cleanupHandler, NULL);
sleep(1);//Note that when you uncomment lines, you should uncomment them in order.
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &o_state);
sleep(1);
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &o_type);
puts("1 Hello World");
sleep(1);
pthread_setcancelstate(o_state, &o_state);
sleep(1);
puts("2 Hello World");
pthread_cleanup_pop(0);
pthread_exit(NULL);
}
int main() {
pthread_t th;
int rc;
rc = pthread_create(&th, NULL, Thread, NULL);
pthread_cancel(th);
pthread_exit(NULL);
}