User guide

August 2001 11

Application Architecture

Processes and Threads

An instance of an executing application is a process. For

example, a word processing program and a spreadsheet that are

executing simultaneously are both processes. You can have

many processes running at once. Each process consists of data,

code, and one or more threads. The processes cannot share data

directly.

Each process can have associated threads that execute

functions of the process. Each process can have more than one

thread, each of which has CPU registers and a stack. The

threads share data as shown in Figure 3.

For example, within the word processing process, you can have

threads for printing, saving, and receiving keyboard data. These

threads can execute simultaneously. The first thread, called the

primary thread, is created when the application starts and

starts executing from the program’s entry point. This thread

can generate new threads, which can generate threads of their

own.