pthread_cleanup_pop with argument 0?

Question

I am studying thread in APUE book 2e

I thought pthread_cleanup_pop functions is for setting the pushed function by pthread_cleanup_push() to be executed or not. So i

Answer 1

did I get pthread_cleanup_pop wrong?

No, you didn't.

The reason your code executed cleanup handlers, is that your control never reaches pthread_cleanup_pop(0). Instead, you always execute return in thr_fn1, and pthread_exit in thr_fn2.

Try creating the threads with pthread_create(&tid1, NULL, thr_fn1, (void *)0); instead of 1. When I do that, I get (expected):

thread 1 start
thread 1 push complete
thread 2 start
thread 2 push complete
thread 1 exit code 1
thread 2 exit code 2