Lecture 2: Kernels and Processes

Transcription

1 Lecture 2: Kerels ad Processes CS170 Sprig UCSB Yag Some of slides are from Chapter 2 of the AD textbook. OSC book. J. Kubiatowicz CS162@UCB

2 What to lear Process Cocept Cotext Switch &Process Schedulig Operatios o Processes Iterprocess Commuicatio

3 Four fudametal OS cocepts Thread Sigle uique executio cotext Program Couter, Registers, Executio Flags, Stack Address Space w/ Traslatio Programs execute i a address space that is distict from the memory space of the physical machie Process A istace of a executig program is a process cosistig of a address space ad oe or more threads of cotrol Dual Mode operatio/protectio Oly the system has the ability to access certai resources The OS ad the hardware are protected from user programs ad user programs are isolated from oe aother by cotrollig the traslatio from program virtual addresses to machie physical addresses

4 Process Cocept Textbook uses the terms job ad process almost iterchageably process memory Process a program i executio; progress i sequetial fashio A process i memory icludes: program couter Stack/heap Data/istructio (text) sectio Need memory protectio ad address traslatio

5 OS Bottom Lie: Ru Programs Program Source Executable Memory istructios 0x000 it mai() { ; } editor compiler istructios data Load & Execute data heap foo.c a.out stack Load istructio ad data segmets of executable file ito memory Create stack ad heap PC: OS 0xFFF Trasfer cotrol to it registers Provide services to it Processor

6 Load a Executable File to Process Header magic umber idicates type of image. Sectio table: a array of (offset, le, startva) Program/data sectios Used by liker; may be removed after fial lik step header text idata wdata symbol table relocatio records program istructios p immutable data (costats) hello\ writable global/static data j, s j, s,p,sbuf it j = 327; char* s = hello\ ; char sbuf[512]; it p() { it k = 0; j = write(1, s, 6); retur(j); }

7 Dual Mode Operatio Hardware provides at least two modes: Kerel mode (or supervisor or protected ) User mode: Normal programs executed What is eeded i the hardware to support dual mode operatio? a bit of state (user/system mode bit) Certai operatios / actios oly permitted i system/kerel mode I user mode they fail or trap User->Kerel trasitio sets system mode AND saves the user PC Operatig system code carefully puts aside user state the performs the ecessary operatios Kerel->User trasitio clears system mode AND restores appropriate user PC retur-from-iterrupt

8 For example: UNIX System Structure User Mode Applicatios Stadard Libs Kerel Mode Hardware

9 User/Keral(Priviledged) Mode syscall User Mode iterrupt exceptio exec Kerel Mode exit Limited HW access Full HW access

10 Simple Memory Protectio i Process code 0000 code 0000 Static Data Static Data heap heap stack Base register stack Program address 1000 >= Boud register < code Static Data heap stack 1100 Memory protectio with two registers Need proper address settig durig program loadig FFFF

11 Aother idea: Address Space Traslatio Program operates i a address space that is distict from the physical memory space of the machie 0x000 Processor traslator Memory 0xFFF

12 A simple address traslatio with Base ad Boud code 0000 code 0000 Static Data heap Static Data heap stack Base Address stack 1000 code 1000 Program address Static Data heap Boud < 0100 stack 1100 Ca the program touch OS? Ca it touch other programs? FFFF

13 Process State As a process executes, it chages state ew: The process is beig created ruig: Istructios are beig executed waitig: The process is waitig for some evet to occur ready: The process is waitig to be assiged to a processor termiated: The process has fiished executio

14 Diagram of Process State

15 Process Cotrol Block (PCB) Iformatio associated with each process Process state Program couter Copy of CPU registers CPU schedulig iformatio Memory-maagemet iformatio Page table Accoutig iformatio I/O status iformatio

16 Cotext Switch Whe CPU switches to aother process with a ew address space, the system must save the state of the old process ad load the saved state for the ew process via a cotext switch. Cotext of a process represeted i the PCB Cotext-switch time is overhead; the system does o useful work while switchig

17 CPU Switch From Process to Process

18 Tyig it together: OS loads process Proc 1 Proc 2 OS Proc code Static Data heap 0000 sysmode Base 1 xxxx 0000 stack code Static Data 1000 Boud xxxx FFFF heap upc PC regs xxxx stack code Static Data heap stack 3080 FFFF

19 Proc 1 Simple B&B: OS gets ready to switch Proc 2 OS Proc code Static Data heap 0000 sysmode Base stack code Static Data 1000 Boud 1100 FFFF heap Retur poit upc PC regs FF stack code Static Data heap stack 3080 FFFF

20 Process Schedulig Queues Job queue set of all processes i the system Ready queue set of all processes residig i mai memory, ready ad waitig to execute Device queues set of processes waitig for a I/O device Processes migrate amog the various queues

21 Ready Queue Ad Various I/O Device Queues

22 Represetatio of Process Schedulig

23 Schedulers Log-term scheduler Selects which processes should be brought ito the ready queue ivoked very ifrequetly (secods, miutes) cotrols the degree of multiprogrammig Short-term scheduler selects which process should be executed ext ad allocates CPU is ivoked very frequetly (millisecods) Þ (must be fast)

24 Process Creatio Paret process create childre processes. process idetified via a process idetifier (pid) Optios i resource sharig Paret ad childre share all resources Childre share subset of paret s resources Paret ad child share o resources Executio Paret ad childre execute cocurretly Paret waits util childre termiate

25 Process Creatio (Cot.) Optios i address space Child duplicate of paret Child has aother program loaded UNIX examples fork system call creates ew process with duplicated address space With a copy of same code ad data. exec system call used after a fork to replace the process memory space with a ew program

26 Uix Fork/Exec/Exit/Wait Example it pid = fork(); Create a ew process that is a cloe of its paret. Fork() > 0 as paret Fork() ==0 child exec*( program [, argvp, evp]); Overlay the callig process virtual memory with a ew program, ad trasfer cotrol to it. iitialize child cotext exec exit(status); Exit with status, destroyig the process. it pid = wait*(&status); Wait for exit (or other status chage) of a child. wait exit

27 Example: Process Creatio i Uix The fork syscall returs twice: it returs a zero to the child ad the child process ID (pid) to the paret. it pid; it status = 0; if (pid = fork()) { /* paret */.. pid = wait(&status); } else { /* child */.. exit(status); } Paret uses wait to sleep util the child exits; wait returs child pid ad status. Wait variats allow wait o a specific child, or otificatio of stops ad other sigals.

28 C Program Forkig Separate Process it mai() { it pid; pid = fork(); /* fork aother process */ if (pid < 0) { /* error occurred */ fpritf(stderr, "Fork Failed"); exit(-1); } else if (pid == 0) { /* child process */ execlp("/bi/ls", "ls", NULL); } else { /* paret process */ wait (NULL); /*paret waits for the child */ exit(0); } }

29 C Program Forkig Separate Process it mai() { it pid, hello=1; pid = fork(); /* fork aother process */ if (pid < 0) { /* error occurred */ fpritf(stderr, "Fork Failed"); exit(-1); } else if (pid == 0) { /* child process */ hello=0; execlp("/bi/ls", "ls", NULL); prit( Child hello =%d, hello); } } else { /* paret process */ } What is prited i child? 0, 1, or othig What is prited i paret? 0, 1, or othig wait (NULL); /*paret waits for the child*/ pritf( hello= %d, hello); exit(0);

30 Uix Fork/Exec/Exit/Wait Example hello=1 Pid>0 it mai() { as paret with it pid, hello=1; old address space pid = fork(); if (pid == 0) { /* child */ hello=0; execlp("/bi/ls", "ls", NULL); pritf( hello=%d, hello); } else { /* paret process */ wait (NULL); pritf( hello=%d, hello); wait exit(0); } } fork() hello==1 Pid==0 child with duplicated address space iitialize child hello=0 cotext exec() reloads address space Old child code is wiped out exit

31 C Program Forkig Separate Process it mai() { it pid, hello=1; pid = fork(); /* fork aother process */ if (pid < 0) { /* error occurred */ fpritf(stderr, "Fork Failed"); exit(-1); } else if (pid == 0) { /* child process */ hello=0; execlp("/bi/ls", "ls", NULL); prit( Child hello =%d, hello); } } else { /* paret process */ } What if execlp() fails? Child prits 0 What is prited i paret? 1 wait (NULL); /*paret waits for the child*/ pritf( hello= %d, hello); exit(0); What is prited i child? othig

32 Shell A shell is a job cotrol system Lets user execute system utilities/applicatios Widows, MacOS, Liux all have shells Typical format: cmd arg1 arg2... arg i/o redirectio <, > filters & pipes ls more Proj 0

33 Summary o Fork() Create a child PCB with ew id Allocate memory for the child ad duplicate everythig from paret Icludig text/heap/stack. But otice child space is a copy of paret space. All file descriptors that are ope i the paret are duplicated i the child. File read()/write() set offsets are shared May evirometal setigs ad shared segemets are iherited by child. Paret/child ca commuicate through shared segemets Add the child process to ready queue Paret memory pages Paret PCB Child memory pages Child PCB

34 I/O Redirectio with dupe2() File descriptor for stadard iput/output/error at Uix 0 stdi stdout, 2 --stderr dup2(it f_orig, it f_ew) duplicate file descriptor Implemet shell commad ls > temp : fd = ope( temp, O_CREAT O_TRUNC O_WRONLY, 0644)) dup2(fd,1) /*Use temp file as the stadard output*/ ls temp pritf( hello\ ) execvp( ls, )

35 Liux Commad: ps Show your processes or others

36 Liux commad: Pstree -A Show Liux processes i a tree structure

37 Liux commad: Top Top - Show all active processes i details

38 Process Termiatio Process executes last statemet ad asks the operatig system to delete it (exit) Output data from child to paret (via wait) Process resources are deallocated Paret may termiate childre processes Task assiged to child is o loger required If paret is exitig

39 Iterprocess Commuicatio Processes withi a system may idepedet or cooperatig with iformatio sharig Cooperatig processes eed iterprocess commuicatio (IPC) Shared memory Message passig

40 Commuicatios Models

41 Iterprocess Commuicatio with Message Passig Direct messages: Processes must ame each other explicitly: sed (P, message) sed a message to process P receive(q, message) receive a message from process Q Idirect messages: Messages are directed ad received from mailboxes (also referred to as ports) Each mailbox has a uique id Processes ca commuicate oly if they share a mailbox

42 Popular Mechaisms for Process Commuicatio Uix sigals Uix Pipe Shared memory IPC i Posix POSIX is the ame of a family of related stadard specified by IEEE to defie API i Uix. Sockets Remote Procedure Calls (RPC)

43 Uix Sigals Proc 1 Proc 2 sigal A evet similar to hardware iterrupt without priorities Usage: iform a user process of a evet For example, user pressed delete key Each sigal is represeted by a umeric value. Examples: 02, SIGINT: iterrupt a process from a termial (Ctrl-C) 09, SIGKILL: termiate a process SIGUSR1, SIGUSR2: user defied. sigal.h defies the sigals A UNIX sigal raised by a process usig a systems call: kill(sigusr1, process_id) a shell commad: kill -s USR1 process_id

44 UNIX Sigals Each sigal is maitaied as a sigle bit i the process table etry of the receivig process the bit is set whe the correspodig sigal arrives (o waitig queues) A sigal is processed as soo as the process eters i user mode 3 ways to hadle a sigal Igore it: sigal(sig#, SIG_IGN) Ru the default hadler: sigal(sig#, SIG_DFL) Ru a user-defied hadler: sigal(sig#, myhadler) Proc 2 Proc 1 sigal

45 Sigal Hadlig /* code for process p */... sigal(sig#, sig_hdlr);... /* ARBITRARY CODE */ void sig_hdlr(...){ /* hadler code */ } Process p SIG# is raised for p sig_hdlr rus i p s address space p resumes executio

46 Example of sigal program #iclude <sigal.h> mai() { void ct(it sig); sigal(sigint, ct); // Cotrol-C pritf("begi coutig ad INTERRUPTs\"); for(;;); /* ifiite loop */ How may times do you have } to push ctrl-c before exit? void ct(it sig) { static it cout=0; pritf("total of %d INTERRUPTS received\", ++cout); }

47 Example of sigal program #iclude <sigal.h> mai() { void ct(it sig); sigal(sigint, ct); // Cotrol-C pritf("begi coutig ad INTERRUPTs\"); for(;;); /* ifiite loop */ } void ct(it sig) { static it cout=0; } How may times do you have to push ctrl-c before exit? NEVER EXIT pritf("total of %d INTERRUPTS received\", ++cout);

48 Example of sigal program Default way (SIG_DFL) to respod with exit() #iclude <sigal.h> mai() { void ct(it sig); sigal(sigint, ct); // Cotrol-C pritf("begi coutig ad INTERRUPTs\"); for(;;); /* ifiite loop */ } void ct(it sig) { static it cout=0; pritf("total of %d INTERRUPTS received\", ++cout); How may times do you have if(cout==1) to push ctrl-c before exit?1, 2, 3 sigal(sigint, SIG_DFL);

49 Example of sigal program #iclude <sigal.h> mai() { void ct(it sig); sigal(sigint, ct); // Cotrol-C pritf("begi coutig ad INTERRUPTs\"); for(;;); /* ifiite loop */ } void ct(it sig) { static it cout=0; pritf("total of %d INTERRUPTS received\", } ++cout); if(cout==1) How may times do you have to push ctrl-c before exit? 2 sigal(sigint, SIG_DFL); // default hadlig for that sigal will occur.

50 UNIX Pipes for Process Commuicatio The process commuicatio through a file-like iterface pipe(fd) creates the pipe ad kerel allocates a buffer with two poiters fd[0] ad fd[1] File read / write calls are used to sed/receive iformatio o the pipe. Processes use fd[1] to write ad fd[0] to read pipe hadles (fd[0] & fd[1]) are copied to the child durig fork() Usage applicatio ls wc Proc 1 pipe fd Proc 2 ls wc it fd[2];... pipe(fd);... Paret Child Write if(fork() == 0) { /* the child */... read(fd[0], ibuf, size);... } else { /* the paret */... write(fd[1], hello, size);... }

51 UNIX Pipes Paret process, P it fd[2]; pipe(fd); fork() write(fd[1], hello, size); Child process, Q /* gets a copy of paret s variables icludig the pipe poiters fd[0] ad fd[1] */ read(fd[0], ibuf, size); pipe for P ad Q write fuctio Folleh FIFO buffer Liux capacity: default 64KB read fuctio

52 I/O pipelie betwee two commads usig pipe() ad dupe2() Shell commad: ls wc Process 1: dup2(fd[1],1) /* use pipe as stdout */ close(fd[0]) execvp( ls, ); Process 2: dup2(fd[0], 0) /*Use pipe as stdi */ close(fd[1]) execvp( wc, ) Who executes pipe(fd)? Who creates Process 1 or process 2? Proc 1 pipe fd Proc 2 ls wc /*close uused part*/

53 I/O pipelie betwee two commads usig pipe() ad dupe2() Shell commad: ls wc pipe(fd) Child Process 1: dup2(fd[1],1) /* use pipe as stdout */ close(fd[0]) execvp( ls, ); Child Process 2: dup2(fd[0], 0) /*Use pipe as stdi */ close(fd[1]) execvp( wc, ) Paret calls pipe(fd) ad creates Processs 1&2 Proc 1 pipe fd Proc 2 ls wc /*close uused part*/ paret s/c-tutorials/pipe.html

54 Process Commuicatio through Shared Memory POSIX shared memory stadard Write process Create shared memory segmet segmet id = shmget(key, size, IPC_CREAT); Attach shared memory to its address space addr= (char *) shmat(id, NULL, flag); write to the shared memory *addr = 1; Detech shared memory shmdt(addr); Read process segmet id = shmget(key, size, 0666); addr= (char *) shmat(id, NULL, 0); c= *addr; shmdt(addr);

55 = read(rfd,rbuf,rmax); File I/O as Commuicatio betwee processes Commuicatio betwee processes: view files as commuicatio chaels (streams) write(wfd, wbuf, wle); = read(rfd,rbuf,rmax); Commuicatio across the world write(wfd, wbuf, wle);

56 Request Respose Protocol i Cliet- Server Commuicatio Cliet (issues requests) write(rqfd, rqbuf, bufle); requests Server (performs operatios) = read(rfd,rbuf,rmax); wait service request write(wfd, respbuf, le); resposes = read(resfd,resbuf,resmax);

57 Sockets i Cliet-server systems A socket: Cocateatio of IP address ad port The socket :80 refers to port 80 o host

58 try { Example: Cliet coectio i Java Make a coectio to server Socket sock = ew Socket(" ",80); IputStream i = sock.getiputstream(); Read data set from serve ad prit BufferedReader bi = ew BufferedReader(ew IputStreamReader(i)); Strig lie; while( (lie = bi.readlie())!= ull) System.out.pritl(lie); } sock.close();

59 Server code: hadlig cliet requests oe by oe ServerSocket sock = ew ServerSocket(80); while (true) { Socket cliet = sock.accept(); // we have a coectio Create a socket to liste Liste for coectios Write date to the socket true); PritWriter pout = ew PritWriter(cliet.getOutputStream(), pout.pritl(ew java.util.date().tostrig()); } cliet.close(); Close the socket ad resume listeig for more coectios

60 Key OS Cocepts so far Processes Memory Protectio, Address Space, Dual Mode States of processes PCB (Process cotrol block) Cotext Switch &Process Schedulig System calls o processes fork, wait, exec, dup2 Process commuicatio UNIX sigals, pipes, shared memory, socket.