main() thread versus one created by pthread_create() - pthreads

Question

I've been creating programs exemplifying concurrency bugs using POSIX threads.
The overall question I have is what is the difference between the main() thread and one created by pthread_create(). My original understanding was that they are pretty much the same but, I'm getting different results from the two programs below.
To expand before showing the code I've written, what I am wondering is: Is there a difference between the following.
int main() {
...
pthread_create(&t1, NULL, worker, NULL);
pthread_create(&t2, NULL, worker, NULL);
...
}
and
int main() {
...
pthread_create(&t1, NULL, worker, NULL);
worker();
...
}
To expand using a full example program. I've made two versions of the same program. They both have the same function worker()
void *worker(void *arg) {
printf("Entered worker function\n");
int myid;
int data = 999;
pthread_mutex_lock(&gidLock);
myid = gid;
gid++;
printf("myid == %d\n", myid);
pthread_mutex_unlock(&gidLock);
if (myid == 0) {
printf("Sleeping since myid == 0\n");
sleep(1);
result = data;
printf("Result updated\n");
}
return NULL;
}
gid and data are globals initialized to 0.
What's the difference between the following main() functions
int main_1() {
pthread_t t1, t2;
int tmp;
/* initialize globals */
gid = 0;
result = 0;
pthread_create(&t1, NULL, worker, NULL);
pthread_create(&t2, NULL, worker, NULL);
pthread_join(t2, NULL);
printf("Parent thread exited worker function\n");
tmp = result;
printf("%d\n", tmp);
pthread_exit((void *) 0);
}
and
int main_2() {
pthread_t t1;
int tmp;
/* initialize globals */
gid = 0;
result = 0;
pthread_create(&t1, NULL, worker, NULL);
worker(NULL);
printf("Parent thread exited worker function\n");
tmp = result;
printf("%d\n", tmp);
pthread_exit((void *) 0);
}
Sample output for main_1()
Entered worker function
myid == 0
Sleeping since myid == 0
Entered worker function
myid == 1
Parent thread exited worker function
0
Result Updated
Sample output for main_2()
Entered worker function
myid == 0
Sleeping since myid == 0
Entered worker function
myid == 1
/* program waits here */
Result updated
Parent thread exited worker function
999
Edit: The program intentionally has a concurrency bug (an atomicity violation). Delays were added by calling sleep() to attempt to force the buggy interleaving to occur. The intention of the program is to be used to test software automatically detecting concurrency bugs.
I would think that main_1() and main_2() are essentially the same program which should result in the same interleaving when run on the same system (or largely the same interleaving; it is indeterminate, but running the same program on the same system only tend explores a small section of the potential scheduling and rarely deviates [1]).
The "desired" output is is that from main_1()
I'm not sure why the thread with myid == 1 stalls and does not return in main_2(). If I had to guess
Thanks for reading this far, and if anyone needs more information I'd be happy to oblige. Here are links to the full source code.
main_1(): https://gist.github.com/2942372
main_2(): https://gist.github.com/2942375
I've been compiling with gcc -pthread -lpthread
Thanks again.
[1] S. Park, S. Lu, Y. Zhou. "CTrigger: Exposing Atomicity Violation Bugs from Their Hiding Places"