CS302 Operating System Week2 Note

Process

• A Process is an execution instance of a program
  • More than one process can execute the same program code

Process vs. program

• A process has states concerning the execution.
  • Which line of codes it is running
  • How much time left before returning the CPU to others
• Linux commands about processes
  • ps: "process status", it can report a vast amount of information about every process in the system.
  • top: allows users to monitor processes and system resource usage on Linux

What is a Shell?

• A shell is a program, open a "terminal", actually launches a "shell" process
  • Bash in linux
• Written in C
  • use getchar() to get your command "ps"
  • syntax checking
  • invoke a function fork() (a system call) to create a new process
    • i.e., becoming a child process of the shell
  • Ask the child process to exec() the program "ps"

Process hierarchy

• Process relationship
  • A parent process will have its child processes
  • Also, a child process will have its child processes
  • This forms a tree hierarchy

System call

• a function call
• exposed by the kernel
• abstract away most low-level details
• Categorizing system calls
  • Process, File system, Memory, Security, Device
• How can we know if a "function' is a system under linux
  • Read the man page "syscalls" under linux

System calls VS Library function call

• Library functions are usually compiled and packed inside an object called the library file
  • In Windows: .DLL - dynamically linked library
  • In Linux: .So - shared objects

What will we learn about Process

• System calls
  • Hoa to program a simple, bare-bone shell?
• Lifecycle and Scheduling
  • How to create processes?
  • How to handle the death of the processes
  • Which process shall get the core next?
• Signals
  • How to suspend a process
• Synchronization

The Memory of a Process

Memory

• Virtual memory
  • Your process virtually owns all your machine's RAM
• Memory-related functions
  • E.g., how to write "malloc()"

File System

• Each disk can have multiple FSs
• An OS may understand different FSs

OS_L02_fundamental

Four Components of a Computer System

• computer hardware
• operating system
• system and application programs
• user(human being or program)