mirror of
https://github.com/jackyzha0/quartz.git
synced 2025-12-27 14:54:05 -06:00
156 lines
5.4 KiB
Markdown
156 lines
5.4 KiB
Markdown
---
|
|
title: "14-processes-and-system-calls"
|
|
aliases:
|
|
tags:
|
|
- cosc204
|
|
- lecture
|
|
---
|
|
|
|
- heirarchical structure in software systems
|
|
- system calls and interrupts
|
|
- representing process in OSs
|
|
- overview of process scheduling
|
|
|
|
# Heirarchical structure
|
|
software systems have modularity
|
|
- os kernel
|
|
- system programs
|
|
- applicatioin programs
|
|
|
|
|
|
## application programs
|
|
Defn: a program that ordinary usrers interact with, running in user space
|
|
|
|
e.g.,
|
|
- word processor
|
|
- video player
|
|
- web browser
|
|
- games
|
|
- etc
|
|
|
|
## system programs/libraries
|
|
Defn: a program which provides general purpose power level function, packeages in a way which is convenient for a user (e.g., sys admin or programmer) to employ
|
|
|
|
system program types include.,
|
|
- file manipulation progarms
|
|
- status info programs
|
|
- network and device management programs
|
|
- compilers assemblers and interpreters
|
|
- various library code
|
|
- command shell programs (e.g., command interpreters)
|
|
|
|
also runs in user space
|
|
|
|
# system calls
|
|
processes issue requests to the kernel by making system calls
|
|
|
|
|
|
|
|
they are requesets to the OS kernel made through interrupt handlers
|
|
|
|
the set of system calls is termed the programmer interface to OS
|
|
|
|
System calls in xv6
|
|
- fork() Create a new process
|
|
- exit() Terminate the current process
|
|
- wait() Wait for a child process to exit
|
|
- kill(pid) Terminate a process identified with pid
|
|
- getpid() Return the ID number of the current process
|
|
- sleep(n) Put the current process into sleep for n seconds
|
|
- exec(filename, *argv) Load a file named filename and execute it with arguments in argv
|
|
- sbrk(n) Update the process memory space by n bytes
|
|
- open(filename, flags) Open a file named filename with flags indicating read/write
|
|
- read(fd, buf, n) Read n bytes from an open file fd into buf
|
|
- write(fd, buf, n) Write n bytes from buf to an open file fd
|
|
- close(fd) Close the open file fd
|
|
- dup(fd) Duplicate the open file fd into another file
|
|
- descriptor (the return value)
|
|
- pipe(p) Create a pipe and return the file descriptors in p
|
|
- chdir(dirname) Change the current working directory of the process to dirname
|
|
- mkdir(dirname) Create a new directory dirname
|
|
- mknod(name, major, minor) Create a device file name with major and minor numbers
|
|
- fstat(fd) Return status information about an open file fd
|
|
- link(f1, f2) Create another name f2 for the file f1
|
|
- unlink(filename) Remove a file named filename
|
|
|
|
## interrupts
|
|
### detecting interrupt
|
|
CPU hardware containes a wire called the interrupt requirest line
|
|
|
|
when a cpu is running an instruction-execute cycle
|
|
- fetch instruction from memory and store it in instruction register
|
|
- decode/execute instruction
|
|
|
|
an extra step is included
|
|
- sense the interrupt request line.
|
|
- it it has a signal, then respond to the interrupt
|
|
|
|
### responding interrupt
|
|
when interrupt detected, CPU switches to kernel space, and a handler function provided by the OS is invoked
|
|
- the context of the current instructionis saved
|
|
- control is transferred to a fixed memory location holding an interrupt-handling routine
|
|
- when the routine is finished, it restores the context of the interrupted process
|
|
|
|
the interrupt vector is an array of lications thta hold the addresses of these interrupt-handling routines. (usually held in low memory)
|
|
|
|
this is hard to do
|
|
- how to restore context?
|
|
- nested handlers?
|
|
|
|
### what causes them
|
|
generated by:
|
|
- errors: e.g., division by zero, invalid memory access
|
|
- I/O device signals:; e.g., completion of IO operation or arrival of network packet
|
|
- system calls (also called trap or soft interrupt) with special instruction (int or svc)
|
|
|
|
a system call generates an interrupt and the OS transfers control to a system call handler
|
|
|
|
# Processes
|
|
a process is dynamic
|
|
|
|
a given program can be executing many times of a given machines: each instance is a separate process
|
|
|
|
process components
|
|
- text section/code section: the program code itself
|
|
- data section: any global variables used by the program
|
|
- process stack: any local variables currently being used
|
|
- program counter: a pointer to some place in the program code
|
|
- contents of CPU registers
|
|
- memory management information
|
|
- device/file allocation information
|
|
- accounting information
|
|
|
|
## process control blocks
|
|
the OS keeps a record of each process in the system, with a data structure called *process control block* (PCB)
|
|
|
|
|
|
|
|
|
|
|
|
## scheduling processes
|
|
processes take turns to run on the CPU. processes wait to run in one of two queues:
|
|
- ready queue: process ready to execute
|
|
- device queue: processes waiting to use a particular device. (one queue per device)
|
|
|
|
generally represented as linked lists
|
|
|
|
## flow of processes
|
|
|
|
|
|
Rounded rectangles are events.
|
|
Rectangles are queues where processes wait.
|
|
Circles are processing resources that serve the events/queues.
|
|
|
|
## process creation
|
|
created by another process: parent process creates a child process
|
|
- process can copy itself using fork
|
|
- child process can then call exec() to load a new program
|
|
- a child process can run concurrently with parent
|
|
- child process can share the resources of its parent if not restricted
|
|
|
|
system start with one process called *init*
|
|
|
|
## procees heirarchy
|
|
processes for a tree
|
|
|