AIX 4.3.3 contains a fix for a libc problem that could cause the AutoLoader to hang during a fork. The AutoLoader is a multithreaded program. One of the threads forks off another process. Forking off a child process causes an image of the parent's memory to be created in the child.
It is possible that locks used by libc.a to manage multiple threads allocating memory from the heap within the same process have been held by a non-forking thread. Since the non-forking thread will not exist in the child process, this lock will never be released in the child, causing the parent to sometimes hang.