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This sequence is the system s physical control flow (or flow of control). z ?cAltering the control flow^Up to now: two mechanisms for changing control flow Jumps and branches Call and return using the stack discipline. Both react to changes in program state. Insufficient for a useful system Difficult for the CPU to react to changes in system state. Data arrives from a disk or a network adapter. Instruction divides by zero User hits ctl-c at the keyboard System timer expires System needs mechanisms for  exceptional control flow 4g"<74g"<  7N]@dExceptional control flowMechanisms for exceptional control flow exists at all levels of a computer system Low level mechanism Exceptions change in control flow in response to a system event (i.e., change in system state) Combination of hardware and OS software Higher level mechanisms Process context switch Signals Nonlocal jumps (setjmp/longjmp) Implemented by either: OS software (context switch and signals). C language runtime library: nonlocal jumps.R U)VVR U)  VV>'_AeSystem context for exceptionsBf ExceptionsException  a transfer of control to the OS in response to some event (i.e., change in processor state)iiCgInterrupt vectorsDh$Asynchronous exceptions (Interrupts)Caused by events external to the processor Indicated by setting the processor s interrupt pin handler returns to  next instruction. Examples: I/O interrupts hitting ctl-c at the keyboard arrival of a packet from a network arrival of a data sector from a disk Hard reset interrupt hitting the reset button Soft reset interrupt hitting ctl-alt-delete on a PC+Z f+Z  f ,EiSynchronous exceptionsCaused by events that occur as a result of executing an instruction: Traps Intentional Examples: system calls, breakpoint traps, special instructions Returns control to  next instruction Faults Unintentional but possibly recoverable Examples: page faults (recoverable), protection faults (unrecoverable). Either re-executes faulting ( current ) instruction or aborts. Aborts unintentional and unrecoverable Examples: parity error, machine check. Aborts current programEq^Eq  ^Fj Trap exampleOpening a File User calls open(filename, options) Function open executes system call instruction int OS must find or create file, get it ready for reading or writing Returns integer file descriptor~'3a /a, >bGkFault example #1Memory reference User writes to memory location That portion (page) of user s memory is currently on disk Page handler must load page into physical memory Returns to faulting instruction Successful on second try&HlFault example #2vMemory reference User writes to memory location Address is not valid Page handler detects invalid address Sends SIGSEG signal to user process User process exits with  segmentation fault &Im ProcessesDef: A process is an instance of a running program. One of the most profound ideas in computer science. Not the same as  program or  processor Process provides each program with two key abstractions: Logical control flow Each program seems to have exclusive use of the CPU. Private address space Each program seems to have exclusive use of main memory. How are these Illusions maintained? Process executions interleaved (multitasking) Address spaces managed by virtual memory system4]959$^4]9  5  9$^JnLogical control flowsKoConcurrent processesTwo processes run concurrently (are concurrent) if their flows overlap in time. Otherwise, they are sequential. Examples: Concurrent: A & B, A & C Sequential: B & C {+5  +Lp!User view of concurrent processesControl flows for concurrent processes are physically disjoint in time. However, we can think of concurrent processes are running in parallel with each other.MqContext switchingProcesses are managed by a shared chunk of OS code called the kernel Not a separate process, but runs as part of user process Control flow passes from one process to another via a context switch. zE9F>96  NrPrivate address spaces/Each process has its own private address space.00Osfork: Creating new processespint fork(void) creates a new process (child process) that is identical to the calling process (parent process) returns 0 to the child process returns child s pid to the parent process Z6 PtFork example #1Key points Parent and child both run same code Distinguish parent from child by return value from fork Start with same state, but each has private copy Including shared output file descriptor Relative ordering of their print statements undefinedz $81^ $31^  QuFork example #25Key points Both parent and child can continue forking& + +RvFork example #35Key points Both parent and child can continue forking& + +SwFork example #45Key points Both parent and child can continue forking& + +TxFork example #55Key points Both parent and child can continue forking& + +Uyexit: Destroying processyvoid exit(int status) exits a process Normally return with status 0 atexit() registers functions to be executed upon exitd6.,70VzZombiesIdea When process terminates, still consumes system resources Various tables maintained by OS Called a  zombie Living corpse, half alive and half dead Reaping Performed by parent on terminated child Parent is given exit status information Kernel discards process What if parent doesn t reap? If any parent terminates without reaping a child, then child will be reaped by init process Only need explicit reaping for long-running processes E.g., shells and servers9 (h9 (  hO?  W{Zombie - Exampleps shows child process as  defunct Killing parent allows child to be reaped MKKX|Nonterminating child exampleY}!wait: Synchronizing with children"int wait(int *child_status) suspends current process until one of its children terminates return value is the pid of the child process that terminated if child_status != NULL, then the object it points to will be set to a status indicating why the child process terminatedR) dZ T) lZ~!wait: Synchronizing with children"[ wait Example  If multiple children completed, will take in arbitrary order Can use macros WIFEXITED and WEXITSTATUS to get information about exit status\waitpidLwaitpid(pid, &status, options) Can wait for specific process Various options,.. B]wait/waitpid example outputs ^exec: Running new programs~int execl(char *path, char *arg0, char *arg1, & , 0) loads and runs executable at path with args arg0, arg1, & path is the complete path of an executable arg0 becomes the name of the process typically arg0 is either identical to path, or else it contains only the executable filename from path  real arguments to the executable start with arg1, etc. list of args is terminated by a (char *)0 argument returns -1 if error, otherwise doesn t return!4:Pgl/3 '! 8.    '      %H MV_ Summarizing#Exceptions Events that require nonstandard control flow Generated externally (interrupts) or internally (traps and faults) Processes At any given time, system has multiple active processes Only one can execute at a time, though Each process appears to have total control of processor + private memory space Spawning Processes Call to fork: one call, two returns Terminating Processes Call exit: one call, no return Reaping Processes Call wait or waitpid Replacing Program Executed by Process Call execl (or variant): one call, (normally) no return ZpZ ZZZ$ZZZZZ&Z8Z p     $$$$$$$$&((,,,,,,,,,,,./abcde f g h i jklmnopqrstuvwxyz{| }!~"#$%&'O   0` .T3f` T3f3f` 999MMM` lff3f3޲` eoHff33Ҷ` ff!` T3f3fffq` T3f3fff[>?" dd@ ?nPd@ d " @ ` n?" dd@   @@``PR   @ ` `$p>>  C; ,(  , , s * "`0  T Click to edit Master title style! ! , c $ "@0  RClick to edit Master text styles Second level Third level Fourth level Fifth level!     S  , c $É ":   AEECS 213 Introduction to Computer Systems Northwestern University2B0(2* 3 3 , Nff??"` , Nff??"` F   ," , Nff??" , Nff??"  , Nff??"  , Nff??"`  , c $̉ "ce  L*"0(2Z , B޽h))? ? T3f3fff[ 0___PPT10.Zj&___PPT92p22 1_aqualab01R  0  0@(  0~ 0 Hff??"A 0 0d "    A Click to edit  0 <  "   T Click to edit Master title style! !T   0 "  0 TГff??"  4 0 0 Tpff??"  4 0~  0 Hff??"A~  0 Hff??"A  0 RAk B?nwu-seal-gray"@P%  0 c $ "`0   !Fabin E. Bustamante, Spring 2007H"0(2 3& 3& 3Z 0 B޽h))? ? T3f3fff[80___PPT10.Zj&( 0 d8(  d  d N`֣yy .   v* a11aa d N,أyy 2 .  x* a11aad d c $ ?  4 d Nyy 9 3  RClick to edit Master text styles Second level Third level Fourth level Fifth level!     S d Tyy q   v* a11aa d Tyy q2   x* a11aaH d 0ηo~ ? 3380___PPT10.eۡ ((    N1 yy .    \* a11aa  NpM yy 2 .   ^* a11aa  Td yy q    \* a11aa  T`h yy q2    ^* a11aaH  0ηo~ ? 3380___PPT10.dz͓ 0L0  $(   r  S  0   r  S ȥ0    H  0޽h ? GGGy___PPT10Y+D=' .= @B +\  0 {  (   ~  s *(,`0     # l)wawa1 ?,@0    <18c? o  "\<startup> inst1 inst2 inst3 & instn <shutdown>/0         H28c?P7 OPhysical control flow0 jB  BD8c? DD   H@88c?P C7  >Time0 H  0޽h ? GGGy___PPT10Y+D=' .= @B +m  0 0$ $(  $ r $ S T,`0   r $ S U,@0  H $ 0޽h ? GGGy___PPT10Y+D=' .= @B +m  0 @( $(  ( r ( S j,`0   r ( S Tk,@0  H ( 0޽h ? GGGy___PPT10Y+D=' .= @B +   0 P'', (  ,  , 3 r@dOdO,`0   XB , 01?XB , @ 01?> XB , 01?p XB , 01?PPGXB , 01?XB , 01?PPXB  , 01? XB  , 01?^^D XB  , 01? d XB  , 01? 0 0 XB  , 01? XB , 01?PP XB , 01?^## XB , 01?\ ^^ XB , 01???  , # l`[`[1))?.  d Local/IO Bus" 0  ???__~~ , # l@`[`[1))?M   ^Memory"0 ???__~~ , # l̚`[`[1))?= 8  gNetwork adapter"0 ???__~~ , # l`[`[1))?M "  kIDE disk controller"0 ???__~~ , # l y`[`[1))?= t  e Video adapter"0 ???__~~ , # l`[`[1))? x  _Display"0 ???__~~ , # l`[`[1))? 0  _Network"0 ???__~~ , # lѨ`[`[1))?0 a Processor" 0  ???__~~ , # l`Ө`[`[1))? lInterrupt controller"0 ???__~~ , # lݨ`[`[1))?M W  gSCSI controller"0 ???__~~ , # l`[`[1))?T w   `SCSI bus" 0  ???__~~  , # l`[`[1))? ' oSerial port controller"0 ???__~~  , # lI`[`[1))? pParallel port controller"0 ???__~~ , # lp I`[`[1))?  kKeyboard controller"0 ???__~~^B  , 61?{{ !, # lI`[`[1))?  `Keyboard" 0  ???__~~ ", # lI`[`[1))? p ]Mouse"0 ???__~~ #, # l0"I`[`[1))? _Printer"0 ???__~~ $, # l0,I`[`[1))? ]Modem"0 ???__~~B %, 3 r06I&e&e g ))?   \disk"0 ???__~~B &, 3 r0@I&e&e g ))? b  \disk"0 ???__~~B ', 3 r0JI&e&e g ))?  s  ]CDROM"0 ???__~~H , 0޽h ? O(3e1y___PPT10Y+D=' .= @B +    0L0   `0 D (  0 r 0 S @i,`0   r 0 S hR,@0   0 Z4XIoaoa1?] B D User Process 0   0 Z]Ioaoa1?] B :OS0 ^B 0 61? ^B 0 61?# # ^B 0 61?'  ^B  0 61?O  ^B  0 61? ?   0 ZaIoaoa1?U :  A exception 0    0 TTgIoaoa1? @  t*exception processing by exception handler .+0   0 ZkIoaoa1? V  \exception return (optional)$0   0 TpIoaoa1?{PK`  >event 0  0 HoI8c?p@mD  Ccurrent 0  0 HTsI8c?   @next 0 jB 0 BD8c? @ H 0 0޽h ? GGGy___PPT10Y+D=' .= @B +   0 p4 W(  4 ~ 4 s **,`0   } 4 s *I,   Each type of event has a unique exception number k Index into jump table (a.k.a., interrupt vector) Jump table entry k points to a function (exception handler). Handler k is called each time exception k occurs.  4 ZIoaoa1?,J Linterrupt vector 0 j 4 B1?P j 4 B1?P  j 4 B1? p |B 4 TD1?X  v2  4 N1? @   4 NI1?r  =0 0   4 NؙI1?@ s  =1 0   4 NI1? s  =2 0   4 NI1? y  ?... 0 j 4 B1?   4 NI1?   ?n-1 0 v2 4 N1?0 |B 4 TD1?  4 TLI1))?` H Zcode for exception handler 0 0  4 TI1))?`  Ycode for exception handler 1 0 v2 4 N1?  |B 4 TD1?  4 T\I1))?X `  Xcode for exception handler 2 0  4 TI1))? `  [code for exception handler n-1 0   4 NlI1?   ?... 0 v2 4 N1?8 p |B 4 TD1?T   4 HԗI8c?T NException numbers 0 jB 4 @ BD8c? H 4 0޽h ? GGGy___PPT10Y+D=' .= @B +m   0 8 $(  8 r 8 S  ,`0   r 8 S ,@0  H 8 0޽h ? GGGy___PPT10Y+D=' .= @B +m   0 < $(  < r < S I,`0   r < S I,@0 I H < 0޽h ? GGGy___PPT10Y+D=' .= @B +   0L0   @ y (  @ r @ S I,`0  I ~ @ s *\I,@0 I  @ ZIoaoa1? py  H User Process 0   @ Z@Ioaoa1?   >OS 0 ^B @ 61?) qq ^B @ 61? u] ^B @ 61? aa"^B @ 61? me*^B  @ 61? qq  @ Zoaoa1?  A exception 0    @ T4oaoa1?X B Open file  0    @ Z oaoa1?  Freturn$0   @ <,8c?   Yint 0  @ <D8c? W ?pop 0  @ B88c?`H .~0804d070 <__libc_open>: . . . 804d082: cd 80 int $0x80 804d084: 5b pop %ebx . . .<0 ?=P 2H @ 0޽h ? GGGy___PPT10Y+D=' .= @B +   0L0   D 6 (  D r D S 1,`0   r D S 02,@0   F  L D   ` D  Z3oaoa1?  H User Process 0   D  Z8oaoa1?  0  >OS 0 fB D  61?Y  fB D  61?  fB D  61? RfB  D 61? ZfB  D  61?9  D  ZX=oaoa1?   B page fault 0    D  TdAoaoa1? LF X Create page and load into memory!0 !  D  ZEoaoa1?   Freturn$0  D  TJoaoa1?. { >event 0  D  HpN8c? xW Zmovl 0 rB D  BD8c? p  D BLR8c?X|0@ )int a[1000]; main () { a[500] = 13; } *0 *' D BS8c?-pp 5 80483b7: c7 05 10 9d 04 08 0d movl $0xd,0x8049d10 60 6 H D 0޽h ? GGGy___PPT10Y+D=' .= @B +   0L0   H  (  H r H S |h,`0   r H S h,@0   H B@j8c? p *int a[1000]; main () { a[5000] = 13; } +0 +( H B p8c?] 5 80483b7: c7 05 60 e3 04 08 0d movl $0xd,0x804e360 60 6 x8 H 0` H  H0` H  Ztoaoa1? e  H User Process 0   H  Zxoaoa1? e  >OS 0 fB H  61? B fB H  61?F  F fB H  61?H J H fB H  61?x   H  Z}oaoa1? x ]  B page fault 0    H  Toaoa1?x e NDetect invalid address0   H  Toaoa1?H C  >event 0   H  H(8c? @  Zmovl 0 rB  H  BD8c?# 8#  H  T8oaoa1?{0` FSignal process0 H H 0޽h ? GGGy___PPT10Y+D=' .= @B +m  0 L $(  L r L S l,`0   r L S (,@0  H L 0޽h ? GGGy___PPT10Y+D=' .= @B +   0   P v (  P ~ P s *ܨ,`0   jB P BD8c?P  P Hh8c?  @Time 0 dB P <D8c?`  P H`8c?p; D E Process A 0   P H8c?p D E Process B 0   P Hp¬8c?pD E Process C 0  dB  P <D8c? ` ` dB  P <D8c?  dB  P <D8c?` dB  P <D8c?`   jB  P BDg ? p jB P BDg ?pjB P BDg ?pjB P BDg ?` p` jB P BDg ? p  P HǬ8c?p i-Each process has its own logical control flow .0 .H P 0޽h ? GGGy___PPT10Y+D=' .= @B +*   0 Q I T  (  T ~ T s *Ԭ,`0   ~ T s *լ,@0  F &0  T   &rB T  BD8c?  T  H ج8c?&   @Time 0 lB T  <D8c?   T  H,ܬ8c?K0 0   E Process A 0    T  H8c? 0   E Process B 0    T  H8c? 0   E Process C 0  lB  T  <D8c?p p lB  T  <D8c?0 0` lB  T  <D8c?`  lB T  <D8c?0 0 rB T  BDg ?  rB T  BDg ?  rB T  BDg ?` ` rB T  BDg ?  rB T  BDg ?  H T 0޽h ? GGGy___PPT10Y+D=' .= @B +   0   X (  X ~ X s *,`0   ~ X s *d,@0  jB X @ BD8c?  X HD8c?   @Time 0 dB X <D8c?  X H8c?  E Process A 0   X HD 8c?k P  E Process B 0    X H 8c?+ E Process C 0  dB  X <D8c?0 dB  X <D8c?  dB  X <D8c? P jB  X BDg ?jB X BDg ?P P dB X <D8c? p jB X BDg ?0 0 jB X BDg ?  H X 0޽h ? GGGy___PPT10Y+D=' .= @B +  0 \ (  \ ~ \ s *!,`0   ~ \ s *!,@0   \ H4#8c?vD  JProcess A code 0  \ H (8c? D  JProcess B code 0 jB \ @ BD8c?) $P jB \ BD8c?P  @ jB \ BD8c?@ ` jB  \ @ BD8c?`  P jB  \ BD8c?P  pjB  \ @ BD8c?( 0 `  \ H$8c?` X (4  E user code 0    \ H08c?e X 9  G kernel code 0   \ H(58c?i X (=  E user code 0   \ H|98c?| M P  G kernel code 0   \ H=8c? X (p E user code 0  jB \ BD8c?5 HX5 jB \ BD8c?B HXB jB \ BD8c?O HXO jB \ BD8c?\ HX\ jB \ BD8c?iHXijB \ BD8c?) HX) jB \ BD8c?0   \ ND8c??   >Time0  \ HI8c?F 4 0  \ <$H8c? 6"0 2 \ B\O8c?4 $  6"0  \ HhS8c?   Xcontext switch.0  \ BY8c?` P  6"0  \ H[8c?L   Xcontext switch.0 H \ 0޽h ? GGGy___PPT10Y+D=' .= @B +E  0 ld ` (  ` ~ ` s * q,`0   ~ ` s *q,@0   ` Z o?&?) ` Hsg ?[  k/kernel virtual memory (code, data, heap, stack) 00 0 ` Hxg ?K[   e)memory mapped region for shared libraries *0 * ` Blzg ? [   4 0  ` Hg ? [ Z  !run-time heap (managed by malloc) "0 "  ` Bg ?[ J 4 0 pB  ` HDg ?A / 0    ` Hg ?[  [user stack (created at runtime) 0  pB  ` HDg ?/ 0 NpB  ` @ HDg ?/ 0 g ` B܍g ?U  Bunused 0  ` N48c?5 ;00  ` N蕭8c?rg p%esp (stack pointer)0 pB ` @ HDg ? ` N8c?R5 Wmemory invisible to user code0 pB ` HDg ?  ` N8c? u  Wbrk0 pB ` @ HDg ?   ` T\ 8c?mL^ - D 0xc0000000 0   ` T8 8c?lL^ , D 0x08048000 0   ` T쬭 8c?- L^  D 0x40000000 0   ` HPg ?Z U   ~ read/write segment (.data, .bss) !0 ! ` HLg ? U  )read-only segment (.init, .text, .rodata) *0 *" ` Z 1?Z / ` N,8c?* Up Z loaded from the executable file!0 ! ` TH 8c?L^  D 0xffffffff 0  |B ` TD)?[ H ` 0޽h ? GGGy___PPT10Y+D=' .= @B +   0 4,0d (  d ~ d s *ѭ,`0   ~ d s *tҭ,@0  A d Bӭg ?vT   aif (fork() == 0) { printf("hello from child\n"); } else { printf("hello from parent\n"); }b0 b,  7 d Hڭ8c?P D>  UFork is interesting (and often confusing) because it is called once but returns twiceNV0 ? H d 0޽h ? GGGy___PPT10Y+D=' .= @B +  0 @h w(  h ~ h s *P,`0   ~ h s *(,@0  3 h Btg ? void fork1() { int x = 1; pid_t pid = fork(); if (pid == 0) { printf("Child has x = %d\n", ++x); } else { printf("Parent has x = %d\n", --x); } printf("Bye from process %d with x = %d\n", getpid(), x); } 0   $ ! H h 0޽h ? GGGy___PPT10Y+D=' .= @B +  0 Pl A(  l ~ l s *4,`0   ~ l s *,@0  7 l Bg ? P t  ivoid fork2() { printf("L0\n"); fork(); printf("L1\n"); fork(); printf("Bye\n"); }j0 jW z  0   l    ,$D 0`B l  0D8c?0  l  H8c? 0    >L0 0 z  p  l  @ ,$D 0fB  l 6D8c? @   p   l #  p ,$D 0`B  l  0D8c? @ p@   l  H8c? 0 .  >L1 0   l  H,#8c? .T  >L1 0 `B l  0D8c? p z p   l   ,$D 0fB l 6D8c?p0 p fB l 6D8c?p p@ `B l  0D8c?p  `B l  0D8c?p0 0  l  H(8c?0   ?Bye 0  l  H,8c?p D  ?Bye 0  l  H/8c? T  ?Bye 0  l  H38c?   ?Bye 0 `B l  0D8c?p  `B l  0D8c?p@ @ H l 0޽h ? GGG___PPT10+AD' .= @B Du' = @BA?%,( < +O%,( < +D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*l %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*l %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*l %(+[  0 }u`##p  (  p ~ p s *D,`0   ~ p s *E,@0  [ p BGg ?p@p n  void fork3() { printf("L0\n"); fork(); printf("L1\n"); fork(); printf("L2\n"); fork(); printf("Bye\n"); }0 { fz    p    ,$D 0fB p 6D8c? @  `B p  0D8c?   p  HB8c?0   >L1 0 `B  p  0D8c? @ @   p  HQ8c? 0 .  >L2 0   p  HHU8c?  .T  >L2 0 fB  p 6D8c?p0 p fB  p 6D8c?p p@ `B p  0D8c?p  `B p  0D8c?p0 0  p  HPZ8c?0   ?Bye 0  p  H^8c?p D  ?Bye 0  p  H\b8c? T  ?Bye 0  p  Hf8c?   ?Bye 0 fB p 6D8c?   `B p  0D8c?   p  Hj8c?   >L1 0 `B p  0D8c?  p  Hi8c?  .  >L2 0  p  Hs8c? P.$ >L2 0 fB p 6D8c?p p fB p 6D8c?pPp`B p  0D8c?pPP`B p  0D8c?p   p  Hq8c?   ?Bye 0  p  H|{8c?@  ?Bye 0   p  H08c?P$ ?Bye 0  !p  H~8c?d ?Bye 0 fB "p 6D8c?   #p  H8c? 0   >L0 0 H p 0޽h ? GGG~___PPT10^+n0DB' .= @B D' = @BA?%,( < +O%,( < +D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*p %(+  0 .&pt (  t ~ t s *d,`0   ~ t s *<,@0  r t Bg ?p  void fork4() { printf("L0\n"); if (fork() != 0) { printf("L1\n"); if (fork() != 0) { printf("L2\n"); fork(); } } printf("Bye\n"); }0  z  @  t    ,$D 0`B t  0D8c? @  t  H䟯8c? .  >L0 0 Mz @;   t   ,$D 0  t  H8c?@ N  >L1 0 `B  t  0D8c?@` 0`   t  H08c?;t  ?Bye 0 fB  t 6D8c?@` @ `B t  0D8c?@ ` l ` ;  t   ,$D 0fB t 6D8c?` ` N ` ;  t  ` ; `B t  0D8c?` 0  t  H48c?` n  >L2 0  t  H`8c? ;  ?Bye 0 `B t  0D8c?`  Nz  ;  t   e ,$D 0fB t 6D8c?  `B t  0D8c? 0  t  H8c? ;  ?Bye 0  t  Hp8c? ;  ?Bye 0 `B t  0D8c?  H t 0޽h ? GGG: 2 ___PPT10 +(?ED ' .= @B D ' = @BA?%,( < +O%,( < +D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*t %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* t %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*t %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*t %(+p  0 x n(  x ~ x s *̯,`0   ~ x s *̯,@0  r x BXg ?p  void fork5() { printf("L0\n"); if (fork() == 0) { printf("L1\n"); if (fork() == 0) { printf("L2\n"); fork(); } } printf("Bye\n"); }0  z P pt  x   P pt ,$D 0`B x  0D8c?P ` p`  x  H\ԯ8c?P ^t  >L0 0 Mz p t  x   pt ,$D 0  x  HLد8c? t  ?Bye 0 fB  x 6D8c?pp p` `B  x  0D8c?pp p   x  Hܯ8c?p ~  >L1 0 `B  x  0D8c?p` ` Nz ;  x  ; ,$D 0fB x 6D8c?   x  H8c? ;  ?Bye 0 `B x  0D8c?   x  H<8c?0  ?Bye 0 `B x  0D8c?  Mz    x    ,$D 0fB x 6D8c? p  x  H8c?   ?Bye 0 `B x  0D8c?   x  H8c?   >L2 0 `B x  0D8c?p p H x 0޽h ? GGG: 2 ___PPT10 +)JD ' .= @B D ' = @BA?%,( < +O%,( < +D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*x %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*x %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*x %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*x %(+  0 | (  | ~ | s *,`0   ~ | s *T,@0  O | Bg ?   ovoid cleanup(void) { printf("cleaning up\n"); } void fork6() { atexit(cleanup); fork(); exit(0); }p0 p,H | 0޽h ? GGGy___PPT10Y+D=' .= @B +  0  <(   ~  s *|,`0   ~  s *T,@0  H  0޽h ? GGGy___PPT10Y+D=' .= @B +  0  (   S  Bd/g ?  ylinux> ./forks 7 & [1] 6639 Running Parent, PID = 6639 Terminating Child, PID = 6640 linux> ps PID TTY TIME CMD 6585 ttyp9 00:00:00 tcsh 6639 ttyp9 00:00:03 forks 6640 ttyp9 00:00:00 forks 6641 ttyp9 00:00:00 ps linux> kill 6639 [1] Terminated linux> ps PID TTY TIME CMD 6585 ttyp9 00:00:00 tcsh 6642 ttyp9 00:00:00 psz0  I TP5_5~  s *$2,`0   ~  s *A,@0    BBg ?   void fork7() { if (fork() == 0) { /* Child */ printf("Terminating Child, PID = %d\n", getpid()); exit(0); } else { printf("Running Parent, PID = %d\n", getpid()); while (1) ; /* Infinite loop */ } } 0  P43H  0޽h ? GGGy___PPT10Y+D=' .= @B +&   0 ME (     B[g ?0  4linux> ./forks 8 Terminating Parent, PID = 6675 Running Child, PID = 6676 linux> ps PID TTY TIME CMD 6585 ttyp9 00:00:00 tcsh 6676 ttyp9 00:00:06 forks 6677 ttyp9 00:00:00 ps linux> kill 6676 linux> ps PID TTY TIME CMD 6585 ttyp9 00:00:00 tcsh 6678 ttyp9 00:00:00 ps50  @r XE57 5r  S b,`0     s *n,7    yChild process still active even though parent has terminated Must kill explicitly, or else will keep running indefinitelyzz  Brg ?p` & void fork8() { if (fork() == 0) { /* Child */ printf("Running Child, PID = %d\n", getpid()); while (1) ; /* Infinite loop */ } else { printf("Terminating Parent, PID = %d\n", getpid()); exit(0); } } 0  P49H  0޽h ? GGGy___PPT10Y+D=' .= @B +y ! 0  0(   r  S 8,`0   ~  s *,@0  H  0޽h ? GGGy___PPT10Y+D=' .= @B + " 0  (   r  S \,`0   !  Bg ?P   void fork9() { int child_status; if (fork() == 0) { printf("HC: hello from child\n"); } else { printf("HP: hello from parent\n"); wait(&child_status); printf("CT: child has terminated\n"); } printf("Bye\n"); exit(); } 0  b. - : $ B  0D8c?  ,$D 0Lz        ,$D 0fB  6D8c?@  `B   0D8c?@ p@    HT8c?0   >HP 0    H,8c? T  >HC 0 `B   0D8c? p z p      K ,$D 0   H|8c?p T  ?Bye 0 `B   0D8c?p@ @ `B   0D8c?p  z @     @ @0 ,$D 0fB   6D8c?@ @ fB   6D8c?@  `B   0D8c?  z 0     0 0> ,$D 0   H8c?0   >CT 0 `B   0D8c?  z 0     0 { ,$D 0   Ht8c?0   ?Bye 0 `B   0D8c?  H  0޽h ? GGG___PPT10+ˊBDn' .= @B D)' = @BA?%,( < +O%,( < +D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* %(+ # 0  N(   r  S ˲,`0   r  S @Ҳ,@0  "  6xӲg ?p |void fork10() { pid_t pid[N]; int i; int child_status; for (i = 0; i < N; i++) if ((pid[i] = fork()) == 0) exit(100+i); /* Child */ for (i = 0; i < N; i++) { /*FIXME  whichever ends first*/ pid_t wpid = wait(&child_status); if (WIFEXITED(child_status)) printf("Child %d terminated with exit status %d\n", wpid, WEXITSTATUS(child_status)); else printf("Child %d terminate abnormally\n", wpid); } }<0 1p' ,)  H  0޽h ? GGGy___PPT10Y+D=' .= @B + $ 0   (   ~  s *,`0   ~  s *x,@0  ]  Bg ?0I@ void fork11() { pid_t pid[N]; int i; int child_status; for (i = 0; i < N; i++) if ((pid[i] = fork()) == 0) exit(100+i); /* Child */ for (i = 0; i < N; i++) { pid_t wpid = waitpid(pid[i], &child_status, 0); if (WIFEXITED(child_status)) printf("Child %d terminated with exit status %d\n", wpid, WEXITSTATUS(child_status)); else printf("Child %d terminated abnormally\n", wpid); }>0 1O 9 ,)  H  0޽h ? GGGy___PPT10Y+D=' .= @B +: % 0 aY (   r  S p,`0     Bg ?" Child 3565 terminated with exit status 103 Child 3564 terminated with exit status 102 Child 3563 terminated with exit status 101 Child 3562 terminated with exit status 100 Child 3566 terminated with exit status 1040   Btg ? RM Child 3568 terminated with exit status 100 Child 3569 terminated with exit status 101 Child 3570 terminated with exit status 102 Child 3571 terminated with exit status 103 Child 3572 terminated with exit status 1040   H%8c?  Using wait (fork10)X0 $  H.8c?`   Using waitpid (fork11)X0  H  0޽h ? GGGy___PPT10Y+D=' .= @B +  & 0 3+  (   ~  s *,<,`0   ~  s *=,@0    <Tg ? p main() { if (fork() == 0) { execl("/usr/bin/cp", "cp", "foo", "bar", 0); } wait(NULL); printf("copy completed\n"); exit(); } 0 >% % H  0޽h ? GGGy___PPT10Y+D=' .= @B + ' 0 0 <(   ~  s *j,`0   ~  s *k,@0  H  0޽h ? GGGy___PPT10Y+D=' .= @B + a 0 P (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.X b 0 ` (   X  C d     S Qd9 3    H  0ηo~ ? 3380___PPT10.X c 0 p (   X  C d     S hd9 3    H  0ηo~ ? 3380___PPT10.aZ d 0  (   X  C d     S dxd9 3    H  0ηo~ ? 3380___PPT10.aZ e 0  (   X  C d     S ,TId9 3    H  0ηo~ ? 3380___PPT10.aZ f 0  (   X  C d     S Id9 3    H  0ηo~ ? 3380___PPT10.aZ g 0  (   X  C d     S `Id9 3    H  0ηo~ ? 3380___PPT10.aZ h 0  (   X  C d   I  S Id9 3  I  H  0ηo~ ? 3380___PPT10.aZ i 0  (   X  C d   I  S Id9 3  I  H  0ηo~ ? 3380___PPT10.aZ j 0  (   X  C d     S Ld9 3    H  0ηo~ ? 3380___PPT10.aZ k 0  (   X  C d     S \bd9 3    H  0ηo~ ? 3380___PPT10.aZ l 0  (   X  C d     S Hd9 3    H  0ηo~ ? 3380___PPT10.@[ m 0  (   X  C d     S ld9 3    H  0ηo~ ? 3380___PPT10.@[ n 0   (   X  C d     S Ѭd9 3    H  0ηo~ ? 3380___PPT10.@[ o 0 0 (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.@[ p 0 @ (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.@[ q 0 P (   X  C d     S nd9 3    H  0ηo~ ? 3380___PPT10.@[ r 0 ` (   X  C d     S ,d9 3    H  0ηo~ ? 3380___PPT10.@[ s 0 p (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.@[ t 0  (   X  C d     S  d9 3    H  0ηo~ ? 3380___PPT10.@[ u 0  (   X  C d     S Ad9 3    H  0ηo~ ? 3380___PPT10.@[ v 0  (   X  C d     S Pd9 3    H  0ηo~ ? 3380___PPT10.@[ w 0  (   X  C d     S ɯd9 3    H  0ηo~ ? 3380___PPT10.@[ x 0  (   X  C d     S 8d9 3    H  0ηo~ ? 3380___PPT10.n] y 0  (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.n] z 0  (   X  C d     S \+d9 3    H  0ηo~ ? 3380___PPT10.n] { 0  (   X  C d     S Wd9 3    H  0ηo~ ? 3380___PPT10.n] | 0  (   X  C d     S $d9 3    H  0ηo~ ? 3380___PPT10.n] } 0  (   X  C d     S 䛲d9 3    H  0ηo~ ? 3380___PPT10.n] ~ 0   (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.n]  0 0$ (  $ X $ C d    $ S 蠣d9 3    H $ 0ηo~ ? 3380___PPT10.n]  0 @( (  ( X ( C d    ( S d9 3    H ( 0ηo~ ? 3380___PPT10.n]  0 P, (  , X , C d    , S 9d9 3    H , 0ηo~ ? 3380___PPT10.n]  0 `0 (  0 X 0 C d    0 S Wd9 3    H 0 0ηo~ ? 3380___PPT10.n]  0 p4 (  4 X 4 C d    4 S ^d9 3    H 4 0ηo~ ? 3380___PPT10.^rD i we=02 ~+H>R$7MSWnHl ' a0 ';O c"w$&(*,.035+7?9S;g={?ACEGIKNP/RCTWV1Oh+'0`U px$8 Xd    EECS 213Fabian E. BustamantepBased on the slides provided with "Computer Systems: A programmer's perspective", R. Bryant and D. O'Hallaron aqualab01Fabian E. Bustamante99Microsoft PowerPoint@Pd @QZ@@ΫחGSg  )'    """)))UUUMMMBBB999|PP3f333f3333f3ffffff3f̙3ff333f333333333f33333333f33f3ff3f3f3f3333f33̙33333f333333f3333f3ffffff3f33ff3f3f3f3fff3ffffffffff3ffff̙fff3fffff3fff333f3f3ff3ff33f̙̙3̙ff̙̙̙3f̙3f333f3333f3ffffff3f̙3f3f3f333f3333f3ffffff3f̙3f3ffffffffff!___wwwThin4'A x(xKʦ """)))UUUMMMBBB999|PP3f3333f333ff3fffff3f3f̙f3333f3333333333f3333333f3f33ff3f3f3f3333f3333333f3̙33333f333ff3ffffff3f33f3ff3f3f3ffff3fffffffff3fffffff3f̙ffff3ff333f3ff33fff33f3ff̙3f3f3333f333ff3fffff̙̙3̙f̙̙̙3f̙3f3f3333f333ff3fffff3f3f̙3ffffffffff!___wwweeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮ՜.+,0   $ ,4<D L :Lecture notesOn-screen Show$CompSci - Northwestern University_## ,ArialTahomaTimes New Roman WingdingsVerdana HelveticaTimes Courier New 1_aqualab01 Exceptional Control Flow Part I Control flowAltering the control flowExceptional control flowSystem context for exceptions ExceptionsInterrupt vectors%Asynchronous exceptions (Interrupts)Synchronous exceptions Trap exampleFault example #1Fault example #2 ProcessesLogical control flowsConcurrent processes"User view of concurrent processesContext switchingPrivate address spacesfork: Creating new processesFork example #1Fork example #2Fork example #3Fork example #4Fork example #5exit: Destroying processZombiesZombie - ExampleNonterminating child example"wait: Synchronizing with children"wait: Synchronizing with children wait Examplewaitpidwait/waitpid example outputsexec: Running new programs Summarizing  Fonts UsedDesign Template Slide Titles#,_W0Fabian E. BustamanteFabian E. Bustamante  !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~      !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxz{|}~Root EntrydO)Pictures2Current UserSummaryInformation(yUPowerPoint Document(MWDocumentSummaryInformation8