Some questions on threads and processes

Question

I was asked these questions in interview (C++ interview). I'm not confident of the answers and would like to know more.

1. Can thread create another thread ?
2. Can process create another process ?
3. Can thread create a process ?
4. Can process create a thread ?

Answer 1

1. Yes, a thread can create another thread. On UNIX this is done (at the low level) through the clone() command, and at the high(er) level, in C coding, through the pthread library.

2. Yes, a process can launch another process. This happens all the time. The most common type of process -> process is through fork().

3. This, I'm unsure. At this point I'd like to mention there are two major types of threads: kernel-level threads and user-level threads. Kernel level threads (in general) are tied to major processes, while user level threads are spawned by these processes (so by kernel level threads). There are exceptions Maybe someone can give a better answer to thread -> process.

4. Yes. See the comment in 3.

Answer 2

Any code that executes can do anything.

That said, processes aren't code -- threads are the things that are actually run, and processes are their enclosing environments. Hence (1) and (3) are true, the rest false.