Zero Threaded Process?

Does a process have to have at least one t开发者_高级运维hread in it? Is it possible for a process to be void of any threads, or does this not make sense?

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 :)

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.

You can choose not to use an explicit threading library, or an operating system that has no concept of threads (and so doesn't call it a thread), but for most modern programming all programs have at least one thread of execution (generally referred to as a main thread or UI thread or similar). If that exits, so does the process.

Thought experiment: what would a process with zero threads of execution do?

In theory, I don't see why not. But it would be impossible with the popular operating systems.

A process typically consists of a few different parts:

• Threads
• Memory space
• File discriptors
• Environment (root directory, current directory, etc.)
• Privileges (UID, etc.)
• Et cetera

In theory, a process could exist with no threads as an RPC server. Other processes would make RPC calls which spawn threads in the server process, and then the threads disappear when the function returns. I don't know of any operating systems that work this way.

On most OSs, the process exits either when the last thread exits, or when the main thread exits.

Note: This ignores the "useless" cases such as zombie processes, which have no threads but don't do anything.

"main" itself is thread. Its a thread that gets executed. So, every process runs on at least one thread.