CSE3320 Operating Systems Processes Jia Rao

Transcription

1 CSE3320 Operating Systems Prcesses Jia Ra Department f Cmputer Science and Engineering

2 Recap f the Last Class Cmputer hardware Time-sharing Space-sharing Characteristics } Lcality, multiple wrking mdes, lad-balancing OS cmpnents Prcess management Memry management File and strage management

3 Prcess Definitin An instance f a prgram running n a cmputer An abstractin that supprts running prgrams An executin stream in the cntext f a particular prcess state A sequential stream f executin in its wn address space Tw parts f a prcess Sequential executin f instructins Prcess state } registers: PC, SP, } Memry: address space, cde, data, stack, heap } I/O status: pen files

4 Prgram v.s. Prcess Prgram!= Prcess Prgram = static cde + data Prcess = dynamic instantiatin f cde + data + files N 1:1 mapping } A prgram can invke many prcesses } Many prcesses f the same prgram

5 The Prcess Mdel (a) Multiprgramming f fur prgrams (b) Cnceptual mdel f 4 independent, sequential prcesses Sequential prcess mde: hiding the effects f interrupts, and supprt blcking system calls (c) Only ne prgram active at any instant

6 Prcess Life Cycle new admit interrupt exit terminated ready running I/O r event cmpletin scheduler dispatch Blcked I/O r event wait Blcked: unable t run, wait fr an event Ready: willing t run, wait fr the CPU

7 Prcess Creatin Principal events that cause prcess creatin System initializatin; fregrund and backgrund Executin f a prcess creatin system User request t create a new prcess; interactive systems Initiatin f a batch jb UNIX example frk system call creates an exactly cpy f calling prcess } Same memry image, envirnment settings, and pen files Child prcess calls execve t change its memry image and run a new prgram

8 Prcess Terminatin Cnditins which terminate prcesses Nrmal exit (vluntary) Errr exit (vluntary) Fatal errr (invluntary) Killed by anther prcess (invluntary)

9 Put it Tgether /* nw create new prcess */ childpid = frk(); char *cnst parmlist[] = {./Hellwrld", NULL}; if (childpid == 0) /* frk() returns 0 t the child prcess */ { sleep(1); printf("child: My parent's PID: %d\n", getppid()); execve(./hellwrld, parmlist) exit(retval); } else /* frk() returns new pid t the parent prcess */ { printf("parent: my child PID: %d\n", childpid); wait(&status); printf("parent: Child's exit cde is: %d\n, WEXITSTATUS(status)); exit(0); }

10 Prcess Hierarchies (Trees) Parent creates a child prcess, child prcesses can create its wn prcess Frms a hierarchy UNIX calls this a "prcess grup init, a special prcess is present in the bt image Try: pstree -h

11 Implementatin f Prcesses Prcess table One entry per prcess Each entry is called a prcess cntrl blck (PCB) Prcess cntrl blck OS data structure cntaining inf assciated with prcesses } Prcess state (ready, running, blcked) } Prgram cunter } CPU registers } Scheduling inf (pririties) } Memry management inf } Accunting inf (elapsed runtime) } Opened files

12 Multiprgramming Rapid switching between prcesses gives the illusin f running multiple prgrams in parallel When t switch t a prcess? Interrupts } I/O interrupt } Timer interrupt Memry fault Trap

13 OS Interrupt Handling Interrupt vectr cntains the address f the interrupt service prcedures Jump table Skeletn f what lwest level f OS des when an interrupt ccurs when a prcess is running

14 Linux Prcesses Prcess descriptr (PCB) State Identifiers Scheduling inf Links File system Virtual memry Prcessr specific cntext

15 Linux Prcess Descriptr State TASK_RUNNING } Running, ready TASK_INTERRUPTABLE } Blcked EXIT_ZOMBIE } Terminated by nt deallcated EXIT_DEAD } Cmpletely terminated

16 Linux Prcess Descriptr (cnt ) Identifiers pid: PID f the prcess/thread tgid: PID f the thread grup leader pgrp: PID f the grup leader Sessin: PID f the sessin leader Hw t get the pinter t a specific prcess? The current macr PID hash table

17 Linux Prcess Descriptr (cnt ) Scheduling infrmatin pri, static_pri, nrmal_pri rt_pririty sched_class } Task->sched_class->pick_next_task(runqueue)

18 Linux Prcess Descriptr (cnt ) Files fs_struct } file system infrmatin: rt directry, current directry files_struct } Infrmatin n pened files

19 Linux Prcess Descriptr (cnt ) Virtual memry mm_struct: describes the cntent f a prcess s virtual memry } The pinter t the page table } Pinters t the virtual memry areas

20 Summary What is a prcess? An instantiatin f a prgram Prgram life cycle Ready, running, blcked, new, terminated Prcess implementatin Prcess table, PCB Multiprgramming Additinal practice Dwnlad Linux kernel surce t yur VM Find the fllwing fields in structure task_struct (PCB) in LINUX_SRC_FOLDER/include/linux/sched.h } Prgram cunter (try t ggle) } Stack pinter } Prcess ID } Opened file descriptrs