CS4500/5500 Operating Systems Processes

Transcription

1 Operating Systems Prcesses Yanyan Zhuang Department f Cmputer Science UC. Clrad Springs Ref. MOS3E, OS@Austin, Clumbia, Rchester

2 Recap f the Last Class Cmputer hardware Time-multiplexed Space-multiplexed OS cmpnents Prcess management Memry management File and strage management 2 Ref. MOS3E, OS@Austin, Clumbia, Rchester

3 Prcess Prcess == Prgram?? 3 Ref. MOS3E, OS@Austin, Clumbia, Rchester

4 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 4 Ref. MOS3E, OS@Austin, Clumbia, Rchester

5 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, stack, heap } I/O status: pened files 5 Ref. MOS3E, OS@Austin, Clumbia, Rchester

6 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 } Running the same prgram twice } A prgram cntains frk() 6 Ref. MOS3E, OS@Austin, Clumbia, Rchester

7 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 7 Ref. MOS3E, OS@Austin, Clumbia, Rchester

8 Prcess Creatin Principal events that cause prcess creatin System initializatin; fregrund and backgrund Executin f a prcess creatin system call User request t create a new prcess; interactive systems Initiatin f a batch jb 8 Ref. MOS3E, OS@Austin, Clumbia, Rchester

9 Prcess Creatin Principal events that cause prcess creatin System initializatin; fregrund and backgrund Executin f a prcess creatin system call User request t create a new prcess; interactive systems Initiatin f a batch jb UNIX example frk system call creates an exact cpy f calling prcess } Same memry image, envirnment settings, and pened files } After frk, caller is parent, newly-created prcess is child 9 Ref. MOS3E, OS@Austin, Clumbia, Rchester

10 Prcess Image in Memry Temprary data: return address, lcal var (Optinal) memry dynamically allcated during executin Cnstants and glbal var Prgram cde 10 Ref. MOS3E, Clumbia, Rchester

11 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 exact cpy f calling prcess } Same memry image, envirnment settings, and pen files } After frk, caller is parent, newly-created prcess is child Child prcess calls execve t change its memry image and run a new prgram 11 Ref. MOS3E, OS@Austin, Clumbia, Rchester

12 After frk() The child prcess returns executing at the exact same pint after its parent called frk() frk() returns twice: the new PID t the parent, and 0 t the child pid= frk(); if (pid == 0) { /* I am the child (0: invalid PID) */ } else { /* I am the parent */ } All memry cntents f parent/child are identical Tw prcesses execute the cde! (parent/child share same text) Bth have the same files pen at the same psitin (pint t the same file bjects) 12 Ref. MOS3E, OS@Austin, Clumbia, Rchester

13 Putting it Tgether /* nw create new prcess */ pid = frk(); char *cnst parmlist[] = {./Hellwrld", NULL}; if (pid == 0) /* frk() returns 0 t the child prcess */ { sleep(1); printf("child: My parent's PID: %d\n", getppid()); execve(./hellwrld, parmlist); printf("retval f Hellwrld: %d\n", retval); exit(retval); } else /* frk() returns new pid t the parent prcess */ { printf("parent: my child PID: %d\n", pid); wait(&status); printf("parent: Child's exit cde is: %d\n, WEXITSTATUS(status)); exit(0); } 13 Ref. MOS3E, OS@Austin, Clumbia, Rchester

14 Prcess Terminatin Cnditins which terminate prcesses Nrmal exit (vluntary) Errr exit (vluntary) Killed by anther prcess (invluntary) 14 Ref. MOS3E, Clumbia, Rchester

15 Prcess Hierarchies (Trees) Parent creates a child prcess, child prcesses can create its wn prcess Frms a hierarchy UNIX: a prcess and all its children and further descendants frm a "prcess grup init, a special prcess present in the bt image Try: pstree -h 15 Ref. MOS3E, OS@Austin, Clumbia, Rchester

16 Prcess Life Cycle new admit timer interrupt r preemptin exit terminated ready running I/O r event cmpletin scheduler dispatch Blcked I/O r event wait Ready: willing t run, wait fr the CPU Blcked: unable t run, wait fr an event 16 Ref. MOS3E, OS@Austin, Clumbia, Rchester

17 Implementatin f Prcesses Prcess table One entry per prcess Each entry is called a prcess cntrl blck (PCB) Prcess cntrl blck (PCB) OS data structure cntaining data assciated with prcesses 17 Ref. MOS3E, OS@Austin, Clumbia, Rchester

18 Linux Prcesses Prcess table: implemented as a linked list/ hashtable Each element: a prcess descriptr f type task_struct Dynamically allcated fr each prcess Prcess descriptr } Cntains all inf abut a specific prcess 18 Ref. MOS3E, OS@Austin, Clumbia, Rchester

19 Linux Prcesses Prcess descriptr (PCB) State Identifiers Scheduling inf File system Virtual memry 19 Ref. MOS3E, Clumbia, Rchester

20 Linux Prcess Descriptr State TASK_RUNNING } Running TASK_INTERRUPTABLE } Blcked EXIT_ZOMBIE } Terminated by nt deallcated EXIT_DEAD } Cmpletely terminated 20 Ref. MOS3E, OS@Austin, Clumbia, Rchester

21 Linux Prcess Descriptr (cnt ) Identifiers pid: PID f the prcess/thread pgrp: PID f the grup leader Hw t get the pinter t a specific prcess? The current macr The init_task macr find_task_by_vpid(pid_t pid) pid* pid_struct = find_get_pid(int pid); task_struct* task = pid_task(pid_struct,pidtype_pid); 21 Ref. MOS3E, OS@Austin, Clumbia, Rchester

22 Linux Prcess Descriptr (cnt ) Files fs_struct } file system infrmatin: rt directry, current directry files_struct } Infrmatin n pened files 22 Ref. MOS3E, OS@Austin, Clumbia, Rchester

23 Summary What is a prcess? An instantiatin f a prgram Prgram life cycle Ready, running, blcked, new, terminated Prcess implementatin Prcess table, PCB 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 23 Ref. MOS3E, OS@Austin, Clumbia, Rchester