Processes and Threads

Part 1:processes

Process:an abstraction of running program.

A CPU can really only run one process at a time, if there is both cores each one of the them can run only one process at a Tim E.

Process Creation

Operating systems need some to create processes. There is four events this 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 is 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-let another process run)
• Blocked (unable to run until some external event happens)

Part 2:threads

Processes and Threads