Processor And Thread

Process and thread fundamentals

Before we start talking about threads, processes, time slices, and all the other wonderful “scheduling concepts,” let's establish an analogy.
What I want to do first is illustrate how threads and processes work. The best way I can think of (short of digging into the design of a realtime system) is to imagine our threads and processes in some kind of situation.

A process as a house

Let's base our analogy for processes and threads using a regular, everyday object — a house.
A house is really a container, with certain attributes (such as the amount of floor space, the number of bedrooms, and so on).
If you look at it that way, the house really doesn't actively do anything on its own — it's a passive object. This is effectively what a process is. We'll explore this shortly.

The occupants as threads

The people living in the house are the active objects — they're the ones using the various rooms, watching TV, cooking, taking showers, and so on. We'll soon see that's how threads behave.

Single threaded

If you've ever lived on your own, then you know what this is like — you know that you can do anything you want in the house at any time, because there's nobody else in the house. If you want to turn on the stereo, use the washroom, have dinner — whatever — you just go ahead and do it.

Multi threaded

Things change dramatically when you add another person into the house. Let's say you get married, so now you have a spouse living there too. You can't just march into the washroom at any given point; you need to check first to make sure your spouse isn't in there!
If you have two responsible adults living in a house, generally you can be reasonably lax about “security” — you know that the other adult will respect your space, won't try to set the kitchen on fire (deliberately!), and so on.
Now, throw a few kids into the mix and suddenly things get a lot more interesting

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