Processes and Threads

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Part 1: Processes

Process: an abstraction of running program.

A CPU can really only run one process at a time, if there are two cores each one of them can run only one process at a time.

Process Creation

Operating systems need some way to create processes. There are four events that cause processes to be created:

1. System initialization
2. Execution of a process creation system call by a running process
3. A user request to create a new process
4. Initiation of a batch job

Daemons: processes that stay in the background to handle some activity such as e-mail, Web pages, news, printing, and so on.

Note: in UNIX, the ps program can be used to list the running processes. In windows, task manager.

Note: in UNIX, only one system call to create a new process: fork. In windows, CreateProcess

Process Termination, usually due to one of the following conditions:

1. Normal exit (voluntary)
2. Error exit (voluntary)
3. Fatal error (involuntary)
4. Killed by another process (involuntary)

Note: exit()  in UNIX and ExitProcess() in Windows

Process States

• Running (actually using the CPU at that instant)
• Ready (runnable; temporaily stopped to let another process run)
• Blocked (unable to run until some external event happens)

Part 2: THREADS

Processes and Threads

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原文地址：http://www.cnblogs.com/elewei/p/4740512.html