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Download "!"#$%&'()*+,'(-.'*+/*' ()*5+)(6+7'(*'#)*+89:%5 !,/+!"35-5+)-+;**+<$=$*5+'>+)+2?5-$:"

Emmeline Reeves
6 years ago
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1 !"#$%&'()*+,'(-.'*+/*' ()*5+)(6+7'(*'#)*+89:%5!"#$%&'()*+,-./01-*(+-(!-23/+4,("56+426!"#$%&'$(%)( 7,8(9:-2;6(!8(<,466-/. 234()*5 C4,*4A(6-B>;,4 7'(*'#)*+B9:%5 D33AE0;1-*(0-.4 *%+,-(&#./ 0(1 2

2 CA$+D'.*6+'>+E9*&-)5F3(4 "+;+4(E*0A/.46(242-,5(E2;?4(F(,4?E6+4,(G;A/46(F(3,-?,;2(0-/*+4, G$49*).*?+503-#A$5+>.':+'($+%.'#$55+-'+)('-A$. "/634*.(3,-0466(>:4*(E+(*44.6()HI(,46-/,04(-,(124,(4G4*+(-00/,6 J46/24(3,-0466(>:4*()HI(;G;EA;KA4(-,(?EG4*(60:4./AE*?(3,E-,E+5 ;%%$).5+-'+95$.H5I+)5+3>+)**+%.'#$55$5+$"$#9&(4+53:9*-)($'95*? LG4*(+:-/?:(2-6+( (0;*(-*A5(4M40/+4(-*4(3,-0466(;+(;(124 LM043+(3-66EKA5(>E+:(A->4,(34,N-,2;*04(+:;*(EN(,/**E*?(;A-*4 K)53#+>9(#&'(5 fork263;>*6(*4>(3,-0466!;aa4.(-*04o(,4+/,*6(+>e04 exit2+4,2e*;+46(->*(3,-0466!;aa4.(-*04o(*4g4,(,4+/,*6 P/+6(E+(E*+-(QR-2KE4S(6+;+/6 wait22;*.(waitpid2>;e+(n-,(;*.(,4;3(+4,2e*;+4.(0:ea.,4* V*.4,6+;*.E*?(+:4(*-*6+;*.;,.(642;*106(-N(+:4(N/*01-*6 DG-E.E*?(E23,-34,(/64(-N(656+42(,46-/,046 L8?8(QW-,@(K-2K6S(0;*(.E6;KA4(;(

3 [0] init [1] Daemon e.g. httpd Login shell Child Child Child Grandchild Grandchild 5 2A$**+@.'4.):5 ;+!"#$$+35+)(+)%%*3#)&'(+%.'4.):+-A)-+.9(5+%.'4.):5+'(+N$A)*>+ '>+-A$+95$.O sh++ P.343()*+L(3"+5A$**+H2-$%A$(+K'9.($Q+;CRC+K$**+<)N5Q+STUUI csh K2V+L(3"+,+5A$**+Htcsh: $(A)(#$6+csh+)-+,EL+)(6+$*5$0A$.$)+ bash K'9.($W;4)3(X+2A$** int main() { char cmdline[maxline];!"#$%&'()*+),)+#-%#($#)'.) /#,01#2,3%,4#)+4#5+ while (1) { /* read */ printf("> "); Fgets(cmdline, MAXLINE, stdin); if (feof(stdin)) exit(0); /* evaluate */ eval(cmdline); 6

4 23:%*$+2A$**+eval+/9(#&'( void eval(char *cmdline) { char *argv[maxargs]; /* argv for execve() */ int bg; /* should the job run in bg or fg? */ pid_t pid; /* process id */ bg = parseline(cmdline, argv); if (!builtin_command(argv)) { if ((pid = Fork()) == 0) { /* child runs user job */ if (execve(argv[0], argv, environ) < 0) { printf("%s: Command not found.\n", argv[0]); exit(0); if (!bg) { /* parent waits for fg job to terminate */ int status; if (waitpid(pid, &status, 0) < 0) unix_error("waitfg: waitpid error"); else /* otherwise, don t wait for bg job */ printf("%d %s", pid, cmdline); 7 DA)-+Y5+)+ZK)#F4.'9(6+8'NX[ L5$.5+4$($.)**?+.9(+'($+#'::)(6+)-+)+&:$ 9534(0-22;*.O(,4;.(-/+3/+O(+534(;*-+:4,(0-22;*. 2':$+%.'4.):5+.9(+Z>'.+)+*'(4+&:$X LM;23A4'(Q.4A4+4(+:E6(XA4(E*(+>-(:-/,6S unix> sleep 7200; rm /tmp/junk # shell stuck for 2 hours ;+ZN)#F4.'9(6X+B'N+35+)+%.'#$55+0$+6'(\-+0)(-+-'+0)3-+>'. unix> (sleep 7200 ; rm /tmp/junk) & [1] 907 unix> # ready for next command 8

5 @.'N*$:+03-A+23:%*$+2A$**+!"):%*$ P9.+$"):%*$+5A$**+#'..$#-*?+0)3-5+>'.+)(6+.$)%5+>'.$4.'9(6+B'N5 K9-+0A)-+)N'9-+N)#F4.'9(6+B'N5[ YEAA(K40-24(R-2KE46(>:4*(+:45(+4,2E*;+4 YEAA(*4G4,(K4(,4;34.(K40;/64(6:4AA(T+53E0;AA5U(>EAA(*-+(+4,2E*;+4 Z-.4,*(V*EM'(-*04(5-/(4M044.(5-/,(3,-0466([/-+;O(5-/,(6:4AA(0;*\+(,/*(;*5( unix> limit maxproc maxproc unix> ulimit -u # csh syntax # bash syntax 9:4(6:4AA(.-46*\+(@*->(>:4*(;(K;0@?,-/*.(]-K(>EAA(X*E6: <5(*;+/,4O(E+(0-/A.(:;334*(;+(;*5(124 9:4(6:4AA\6(,4?/A;,(0-*+,-A(^->(0;*\+(,4;3(4ME+4.(K;0@?,-/*.(3, (E*(;( 124A5(N;6:E-* J4?/A;,(0-*+,-A(^->(E6(Q>;E+(/*1A(,/**E*?(]-K(0-23A4+46O(+:4*(,4;3(E+S 2'*9&'(1+!"#$%&'()*+#'(-.'*+^'0 9:4(@4,*4A(>EAA(E*+4,,/3+(,4?/A;,(3,-0466E*?(+-(;A4,+(/6(>:4*(;(K;0@?,-/*.( 3,-0466(0-23A4+46 )*(V*EMO(+:4(;A4,+(240:;*E62(E6(0;AA4.(;(+*6(,3 10

6 234()*5 ;+!%&'($+35+)+5:)**+:$55)4$+-A)-+('&_$5+)+%.'#$55+-A)-+)(+$=$(-+ '>+5':$+-?%$+A)5+'##9..$6+3(+-A$+5?5-$: 3, E?*;A(+534(E6(E.4*1X4.(K5(62;AA(E*+4?4,()7_6(T&#`aU -*A5(E*N-,2;1-*(E*(;(6E?*;A(E6(E+6()7(;*.(+:4(N;0+(+:;+(E+(;,,EG ,:# 8#.,%34);$&'( <'//#+5'(0*(6)!2#(4 ` 2YaY7C C$.:3()-$ Y(-$..9%-+H$O4OQ+#-*W#+>.':+F$?N').6I T 2YabY<< C$.:3()-$ b3**+%.'4.):+h#)(('-+'=$..36$+'.+34('.$i SS 2Ya2!ac C$.:3()-$+R+V9:% 2$4:$(-)&'(+=3'*)&'( Sd 2Ya;<GE C$.:3()-$ C3:$.+534()* SU 2Ya,M<V Y4('.$,A3*6+5-'%%$6+'.+-$.:3()-$6 11 2$(63(4+)+234()* b$.($*+!#')!+h6$*3=$.5i+)+534()*+-'+)+)#!*'(*+',-.+/#!!+n?+ 9%6)&(4+5':$+5-)-$+3(+-A$+#'(-$"-+'>+-A$+6$5&()&'(+%.'#$55 b$.($*+5$(65+)+534()*+>'.+'($+'>+-a$+>'**'03(4+.$)5'(51 C4,*4A(:;6( (;(656+42(4G4*+(6/0:(;6(.EGE.4#K5#R4,-(T")bWPLU(-,(+:4( +4,2E*;1-*(-N(;(0:EA.(3,-0466(T")b!=c7U 12

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

8 15 234()*+,'(#$%-5+ b$.($*+:)3(-)3(5+pending+)(6+blocked+n3-+=$#-'.5+3(+-a$+ #'(-$"-+'>+$)#A+%.'#$55 pending'(,43,464*+6(+:4(64+(-n(34*.e*?(6e?*;a6 /'.$W 4.'9(6 B'N K)#FW 4.'9(6 B'N+eS K)#FW 4.'9(6 B'N+e` 34+..,A3*6,A3*6 pid=10 pgid=10?'/#6/'%(0) 3(/2&.+4') -.+/#!!,&.+4-,56 B,$C6/'%(0 5/'$#++)6/'%5)DA pid=20 pgid=20 pid=32 pgid=32 pid=40 pgid=40 pid=21 pgid=20 pid=22 pgid=20 getpgrp() 5+$&%"26%('+##27%(&62(82'&%%+"$26%('+## setpgid() 94:"7+26%('+##27%(&62(82:26%('+##

9 /bin/kill %.'4.):+ 5$(65+).N3-.).?+534()*+-'+)+ %.'#$55+'.+%.'#$55+4.'9%!"):%*$5 /bin/kill $(6+2YabY<<+-'+%.'#$55+`dgSg /bin/kill $(6+2YabY<<+-'+$=$.?+%.'#$55+3(+ %.'#$55+4.'9%+`dgSU linux>./forks 16 Child1: pid=24818 pgrp=24817 Child2: pid=24819 pgrp=24817 linux> ps PID TTY TIME CMD pts/2 00:00:00 tcsh pts/2 00:00:02 forks pts/2 00:00:02 forks pts/2 00:00:00 ps linux> /bin/kill linux> ps PID TTY TIME CMD pts/2 00:00:00 tcsh pts/2 00:00:00 ps linux> 17 2$(63(4+234()*5+>.':+-A$+b$?N').6 953E*?(0+,A#0(T0+,A#RU(64*.6(;(")b)d9(T")b9"9PU(+-(4G4,5(]-K(E*(+:4(N-,4?,-/*.( 3,-0466(?,-/38 2YaY7C+h+6$>)9*-+)#&'(+35+-'+-$.:3()-$+$)#A+%.'#$55+ 2YaC2C@+h+6$>)9*-+)#&'(+35+-'+5-'%+H595%$(6I+$)#A+%.'#$55 pid=10 pgid= pid=20 pgid=20 /'.$W 4.'9(6 B'N K)#FW 4.'9(6 B'N+eS pid=32 pgid=32 K)#FW 4.'9(6 B'N+e` pid=40 pgid=40,a3*6,a3*6 3(/2&.+4') -.+/#!!,&.+4-,56 B,$C6/'%(0 5/'$#++)6/'%5)DA pid=21 pgid=20?'/#6/'%(0) 5/'$#++)6/'%5)@A pid=22 pgid=20 18

10 !"):%*$+'>+ctrl-c+)(6+ctrl-z 219k>./forks 17 Child: pid=28108 pgrp=28107 Parent: pid=28107 pgrp=28107 <types ctrl-z> Suspended 219k> ps w PID TTY STAT TIME COMMAND pts/8 Ss 0:00 -tcsh pts/8 T 0:01./forks pts/8 T 0:01./forks pts/8 R+ 0:00 ps w 219k> fg./forks 17 <types ctrl-c> 219k> ps w PID TTY STAT TIME COMMAND pts/8 Ss 0:00 -tcsh pts/8 R+ 0:00 ps w 2C;C+H%.'#$55+5-)-$I+<$4$(61 7%.!8,$#9#.: 21+5*$$%3(4 C1+5-'%%$6 G1+.9((3(4 ;#/+'),$#9#.: 51+5$553'(+*$)6$. i1+>'.$4.'9(6+%.'#+4.'9% 2$$+Z:)(+%5X+>'.+:'.$+ 6$-)3*5 19 2$(63(4+234()*5+03-A+kill+/9(#&'( void fork12() { pid_t pid[n]; int i, child_status; for (i = 0; i < N; i++) if ((pid[i] = fork()) == 0) while(1); /* Child infinite loop */ /* Parent terminates the child processes */ for (i = 0; i < N; i++) { printf("killing process %d\n", pid[i]); kill(pid[i], SIGINT); /* Parent reaps terminated children */ for (i = 0; i < N; i++) { 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 terminated abnormally\n", wpid); 20

11 G$#$3=3(4+234()*5 29%%'5$++F$.($*+35+.$-9.(3(4+>.':+)(+$"#$%&'(+A)(6*$.+)( $)6?+-'+%)55+#'(-.'*+-'+%.'#$55+b$.($*+#':%9-$5 pnb = pending & ~blocked 9:4(64+(-N(34*.E*?(*-*KA-0@4.(6E?*;A6(N-,(3,-0466(- Y>++Hpnb == 0I+!*5$ P;66(0-*+,-A(+-(*4M+(E*6+,/01-*(E*(+:4(A-?E0;A(^->(N-,(- J434;+(N-,(;AA(*-*R4,-(2(E*(pnb!:--64(A4;6+(*-*R4,-(KE+(2(E*(pnb ;*.(N-,04(3,-0466(-(+-(/#$#*2#( 6E?*;A(2 9:4(,404E3+(-N(+:4(6E?*;A(+,E??4,6(6-24(,$&'((K5(- P;66(0-*+,-A(+-(*4M+(E*6+,/01-*(E*(A-?E0;A(^->(N-,(- 21 V$>)9*-+;#&'(5!)#A+534()*+-?%$+A)5+)+%.$6$_($6+)#<(4$8,(/*+'Q+0A3#A+35+ '($+'>1 9:4(3,-0466(+4,2E*;+46 9:4(3,-0466(+4,2E*;+46(;*.(./236(0-,4 9:4(3,-0466(6+-36(/*1A(,46+;,+4.(K5(;(")b!Id9(6E?*;A 9:4(3,-0466(E?*-,46(+:4(6E?*;A 22

12 Y(5-)**3(4+234()*+M)(6*$.5 CA$+signal+>9(#&'(+:'63_$5+-A$+6$>)9*-+)#&'(+)55'#3)-$6+03-A+ -A$+.$#$3%-+'>+534()*+signum1 handler_t *signal(int signum, handler_t *handler) V3j$.$(-+=)*9$5+>'.+handler1 ")be)bd'(e?*-,4(6e?*;a6(-n(+534(signum ")be7wc'(,4g4,+(+-(+:4(.4n;/a+(;01-*(-*(,404e3+(-n(6e?*;a6(-n(+534(signum I+:4,>E64O(handler(E6(+:4(;..,466(-N(;(+*6(,3)>,(03#/!;AA4.(>:4*(3,-0466(,404EG46(6E?*;A(-N(+534(signum J4N4,,4.(+-(;6(E*(+4,33*(6F)+:4(:;*.A4, LM40/1*?(:;*.A4,(E6(0;AA4.(E$,4$>*(6F)-,(E>,(03*(6F)+:4(6E?*;A E*6+,/01-*(E*(+:4(0-*+,-A(^->(-N(+:4(3,-0466(+:;+(>;6(E*+4,,/3+4.(K5(,404E3+(-N(+:4(6E?*;A ()*+M)(6*3(4+!"):%*$ void int_handler(int sig) { safe_printf("process %d received signal %d\n", getpid(), sig); exit(0); void fork13() { pid_t pid[n]; int i, child_status; signal(sigint, int_handler); for (i = 0; i < N; i++) if ((pid[i] = fork()) == 0) { Killing process Process received signal 2 while(1); /* child infinite Process loop received signal 2 Process received signal 2 for (i = 0; i < N; i++) { Process received signal 2 printf("killing process %d\n", Process pid[i]); received signal 2 kill(pid[i], SIGINT); for (i = 0; i < N; i++) { pid_t wpid = wait(&child_status); 219k>./forks 13 Killing process Killing process Killing process Killing process Child terminated with exit status 0 Child terminated with exit status 0 Child terminated with exit status 0 Child terminated with exit status 0 if (WIFEXITED(child_status)) Child terminated with exit status 0 printf("child %d terminated 219k> with exit status %d\n", wpid, WEXITSTATUS(child_status)); else printf("child %d terminated abnormally\n", wpid); 24

13 234()*5+M)(6*$.5+)5+,'(#9..$(-+/*'05 ;+534()*+A)(6*$.+35+)+5$%).)-$+*'43#)*+^'0+H('-+%.'#$55I+-A)-+.9(5+#'(#9..$(-*?+03-A+-A$+:)3(+%.'4.):+! Q0-*0/,,4*+A5S(E*(+:4(Q*-+(64[/4*1;AS(64*64( G/'$#++);) while (1) ; G/'$#++); handler(){ G/'$#++)B C3:$ 25 ;('-A$.+c3$0+'>+234()*+M)(6*$.5+)5+,'(#9..$(-+/*'05 =.+/#!!,> =.+/#!!,3 3-7":.2;+.-,+%+; 3-7":.2%+'+-,+; Y #9.. Y ($"- 95$.+#'6$+H:)3(I F$.($*+#'6$ 95$.+#'6$+H:)3(I F$.($*+#'6$ 95$.+#'6$+HA)(6*$.I F$.($*+#'6$ 95$.+#'6$+H:)3(I /+'8#?8,!@%8/" /+'8#?8,!@%8/" 26

14 234()*+M)(6*$.+/9(F3($55 int ccount = 0; void child_handler(int sig) { int child_status; pid_t pid = wait(&child_status); ccount--; safe_printf( "Received signal %d from process %d\n", sig, pid); void fork14() { pid_t pid[n]; int i, child_status; ccount = N; signal(sigchld, child_handler); for (i = 0; i < N; i++) if ((pid[i] = fork()) 219k> == 0)./forks { 14 sleep(1); /* deschedule child */ P4*.E*?(6E?*;A6(;,4(*-+( [/4/4. /'.+$)#A+534()*+-?%$Q+B95-+ A)=$+53(4*$+N3-+3(63#)&(4+ 0A$-A$.+'.+('-+534()*+35+ %$(63(4!=$(+3>+:9*&%*$+%.'#$55$5+ A)=$+5$(-+-A35+534()* Received SIGCHLD signal 17 for process exit(0); /* Child: Received Exit */ SIGCHLD signal 17 for process while (ccount > 0) pause(); /* Suspend until signal occurs */ 27 <3=3(4+D3-A+7'(k9$93(4+234()*5 E95-+#A$#F+>'.+)**+-$.:3()-$6+B'N5 953E0;AA5(A--3(>E+:(wait void child_handler2(int sig) { int child_status; pid_t pid; while ((pid = waitpid(-1, &child_status, WNOHANG)) > 0) { ccount--; safe_printf("received signal %d from process %d\n", sig, pid); void fork15() { k>./forks 15 Received signal 17 from process Received signal 17 from process signal(sigchld, Received child_handler2); signal 17 from process Received signal 17 from process Received signal 17 from process k> 28

15 E'.$+234()*+M)(6*$.+/9(F3($55 234()*+)..3=)*+69.3(4+*'(4+5?5-$:+#)**5+H5)?+)+readI 234()*+A)(6*$.+3(-$..9%-5+read+#)** ce*/m'(/3-*(,4+/,*(n,-2(6e?*;a(:;*.a4,o(+:4(read(0;aa(e6(,46+;,+4.( ;/+-2;10;AA5 "-24(-+:4,(^;G-,6(-N(V*EM(0;*(0;/64(+:4(read 0;AA(+-(N;EA(>E+:(;*( EINTER 4,,-,(*/2K4,(TerrnoU E*(+:E6(0;64O(+:4(;33AE0;1-*(3,-?,;2(0;*(,46+;,+(+:4(6A->(656+42(0;AA 29N-*$+63j$.$(#$5+*3F$+-A$5$+#':%*3#)-$+-A$+0.3&(4+'>+%'.-)N*$+ 29 #include <stdlib.h> #include <stdio.h> #include <signal.h> void handler(int sig) { safe_printf("you think hitting ctrl-c will stop the bomb?\n"); sleep(2); safe_printf("well..."); sleep(1); printf("ok\n"); exit(0); main() { 219k> signal(sigint, handler); /* installs ctl-c handler */ while(1) { $"-$.()*O# 219k>./external <ctrl-c> You think hitting ctrl-c will stop the bomb? Well...OK 30

16 a$($.)-$6+!=$(-5 #include <stdio.h> #include <signal.h> int beeps = 0; /* SIGALRM handler */ void handler(int sig) { safe_printf("beep\n"); if (++beeps < 5) alarm(1); else { safe_printf("boom!\n"); exit(0); 3(-$.()*O# main() { signal(sigalrm, handler); alarm(1); /* send SIGALRM in 1 second */ while (1) { /* handler returns here */ 219k>./internal BEEP BEEP BEEP BEEP BEEP BOOM! 219k> 31 ;5?(#W234()*W2)>$-?+ /9(#&'(+35+(!A'/B!%&'($B!(<#,3>+$3-A$.+.$$(-.)(-+H)**+=).3)N*$5+ 5-'.$6+'(+5-)#F+>.):$Q+,21;@@`$+S`OUO`I+'.+('(W3(-$..9%&N*$+N?+ write(e6(-*(+:4(ae6+o(printf i6(*-+ P($+5'*9&'(1+)5?(#W534()*W5)>$+0.)%%$.+>'.+printf: void safe_printf(const char *format,...) { char buf[maxs]; va_list args; va_start(args, format); /* reentrant */ vsnprintf(buf, sizeof(buf), format, args); /* reentrant */ va_end(args); /* reentrant */ write(1, buf, strlen(buf)); /* async-signal-safe */ 5)>$l%.3(mO# 32

17 V64N/A(N-,(4,,-,(,40-G4,5(;*.(6E?*;A(:;*.AE*? int setjmp(jmp_buf j) Z/6+(K4(0;AA4.(K4N-,4(A-*?]23 ).4*1X46(;(,4+/,*(6E+4(N-,(;(6/K64[/4*+(A-*?]23!;AA4.(-*04O(,4+/,*6(-*4(-,(2-,4(1246 Y:%*$:$(-)&'(1 J4242K4,(>:4,4(5-/(;,4(K5(6+-,E*?((+:4(0/,,4*+(/#6*+4#/)$'(4#"4O(+4,$C) 5'*(4#/O((;*.)G<)2,3%#)E*(jmp_buf J4+/,*(a 33 setjmp/longjmp+h#'(-i void longjmp(jmp_buf j, int i) Z4;*E*?',4+/,*(N,-2(+:4(setjmp(,4242K4,4.(K5(]/23(K/f4,(j(;?;E*(888( g(+:e6(124(,4+/,*e*? i(e*6+4;.(-n(a!;aa4.(;b4,(setjmp!;aa4.(-*04o(k/+(*4g4,(,4+/,*6 longjmp+y:%*$:$(-)&'(1 K/f4,(j "4+(%eax2T+:4(,4+/,*(G;A/4U(+-(i h/23(+-(+:4(a-0;1-*(e*.e0;+4.(k5(+:4(p!(6+-,4.(e*(]/23(k/n(j 34

18 setjmpflongjmp+!"):%*$ #include <setjmp.h> jmp_buf buf; main() { if (setjmp(buf)!= 0) { printf("back in main due to an error\n"); else printf("first time through\n"); p1(); /* p1 calls p2, which calls p3 */... p3() { <error checking code> if (error) longjmp(buf, 1) 35 <3:3-)&'(5+'>+7'(*'#)*+89:%5 D'.F5+03-A3(+5-)#F+635#3%*3($!;*(-*A5(A-*?(]/23(+-(4*GE,-*24*+(-N(N/*01-*(+:;+(:;6(K44*(0;AA4.(K/+( *-+(54+(0-23A4+4. jmp_buf env; P1() { if (setjmp(env)) { /* Long Jump to here */ else { P2(); P2() {... P2();... P3(); P3() { longjmp(env, 1); env <+8(%+2.("7=>6?@+%2.("7=>6 P1 P2 P2 P2 P3 P1 36

19 <3:3-)&'(5+'>+<'(4+89:%5+H#'(-OI D'.F5+03-A3(+5-)#F+635#3%*3($!;*(-*A5(A-*?(]/23(+-(4*GE,-*24*+(-N(N/*01-*(+:;+(:;6(K44*(0;AA4.(K/+( *-+(54+(0-23A4+4. P1 jmp_buf env; P1() { P2(); P3(); env P2?$2#+$=>6 P2() { if (setjmp(env)) { /* Long Jump to here */ P3() { longjmp(env, 1); env A P1 P2 *B2%+$&%"# env A P1 P3?$2.("7=>6 CA)-+G$5-).-5+Y-5$*>+DA$(+ctrl-cJ6 #include <stdio.h> #include <signal.h> #include <setjmp.h> sigjmp_buf buf; void handler(int sig) { siglongjmp(buf, 1); main() { signal(sigint, handler); if (!sigsetjmp(buf, 1)) printf("starting\n"); else printf("restarting\n"); 219k>./restart starting processing... processing... processing... restarting processing... processing... restarting processing... processing... processing... 9$%.C' 9$%.C' while(1) { sleep(1); printf("processing...\n");.$5-).-o# 38

20 29::).? 234()*5+%.'=36$+%.'#$55W*$=$*+$"#$%&'(+A)(6*3(4!;*(?4*4,;+4(N,-2(/64,(3,-?,;26!;*(.4X*4(4f40+(K5(.40A;,E*?(6E?*;A(:;*.A4, 2':$+#)=$)-5 i4,5(:e?:(-g4,:4;. I*A5(/64(N-,(4M0431-*;A(0-*.E1-*6 7-*_+(:;G4([/4/46 h/6+(-*4(ke+(n-,(4;0:(34*.e*?(6e?*;a(+534 7'(*'#)*+B9:%5+%.'=36$+$"#$%&'()*+#'(-.'*+^'0+03-A3(+ %.'#$55 39

Exceptional Control Flow: Signals and Nonlocal Jumps

Exceptional Control Flow: Signals and Nonlocal Jumps CS-281: Introduction to Computer Systems Instructor: Dr. Thomas C. Bressoud 1 ECF Exists at All Levels of a System Exceptions Hardware and operating