Question

OS : FreeBSD 8.2 on Oracle VM Virtual Box

I am trying to test that a process attempting to acquire a read lock will be blocked until it is able to acquire it. After initializing rw_lock in Process #1 and locking the lock as a writer I create a second process which attempts to acquire the lock as a reader using blocking rw_rlock(). What I am shooting for is for process #2 to be blocked until process #1 releases Write lock so I am attempting to use pause to insure that process #2 has enough time to be scheduled. However this same pause somehow crashes the system in this scenario since if it is removed the program runs fine. If I replace the pause with a busy loop in Process #1, Process #2 does not get scheduled until Process #1 finishes so it ruins the point of the test. DELAY() also does not allow Process #2 to be scheduled. Any pointers would be appreciated.

Process #1:

static void test_rw_rlock(void)
{ 
    const int seconds = 1;
    rw_init(pResourceLock, "RWLock");
    rw_wlock(pResourceLock);
    kproc_create(&use_rw_rlock, NULL, NULL, 0, 0, "use_rw_rlock()");
    pause("---", hz * seconds);
    rw_wunlock(pResourceLock);
    rw_destroy(pResourceLock);
}

Process #2 :

static void use_rw_rlock(void* arg)
{
    rw_rlock(pResourceLock);
    rw_unlock(pResourceLock);
    kproc_exit(0);
}

Answer 1

Sleeping while hold a rw lock is a no-no.