Zero Threaded Process?

Question

Does a process have to have at least one thread in it? Is it possible for a process to be void of any threads, or does this not make sense?

Answer 1

A process usually has at least one thread. Wikipedia has the definition:

a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process.

The MSDN backs this up:

A processor executes threads, not processes, so each application has at least one process, and a process always has at least one thread of execution, known as the primary thread.

Though it does go on to say:

A process can have zero or more single-threaded apartments and zero or one multithreaded apartment.

Which implies that if both the number of single-threaded apartments and multithreaded apartments could be zero. However, the process wouldn't do much :)

Answer 2

In Unix-like operating systems, it's possible to have a zombie process, where an entry still exists in the process table even though there are no (longer) any threads.