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.
The kernel's role
The house analogy is excellent for getting across the concept of synchronization, but it falls down in one major area. In
our house, we had many threads running simultaneously. However, in a real live system, there's typically only one CPU, so only one "thing" can run at once.
Threads and processes
Let's return to our discussion of threads and processes, this time from the perspective of a real live system. Then, we'll
take a look at the function calls used to deal with threads and processes.
Scheduling and the real world
So far we've talked about scheduling policies and thread states, but we haven't said much yet about why and when things are rescheduled. There's a common misconception that rescheduling just "occurs," without any real causes. Actually, this is a useful abstraction during design! But it's important to understand the conditions
that cause rescheduling. Recall the diagram "Scheduling roadmap" (in the "The kernel's role" section).