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CMU CS 15213 - 16-virtual-memory

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Slide 1SignalsSignal Handlers as Concurrent FlowsTodaySending Signals from the KeyboardExample of ctrl-c and ctrl-zSignal Handler FunkinessLiving With Nonqueuing SignalsSignal Handler Funkiness (Cont.)A Program That Reacts to Externally Generated Events (Ctrl-c)A Program That Reacts to Internally Generated EventsA Program That Reacts to Internally Generated EventsSummaryTodayNonlocal Jumps: setjmp/longjmpsetjmp/longjmp (cont)setjmp/longjmp ExampleLimitations of Nonlocal JumpsLimitations of Long Jumps (cont.)Slide 20TodayVirtual Memory (Previous Lectures)Problem 1: How Does Everything Fit?Problem 2: Memory ManagementProblem 3: How To ProtectSolution: Level Of IndirectionAddress SpacesA System Using Physical AddressingA System Using Virtual AddressingWhy Virtual Memory (VM)?TodayVM as a Tool for CachingMemory Hierarchy: Core 2 DuoDRAM Cache OrganizationAddress Translation: Page TablesAddress Translation With a Page TablePage HitPage MissHandling Page FaultHandling Page FaultHandling Page FaultHandling Page FaultWhy does it work? LocalityTodayVM as a Tool for Memory ManagementVM as a Tool for Memory ManagementSimplifying Linking and LoadingTodayVM as a Tool for Memory ProtectionTodayAddress Translation: Page HitAddress Translation: Page FaultCarnegie MellonIntroduction to Computer Systems15-213/18-243, spring 200916th Lecture, Mar. 17thInstructors: Gregory Kesden and Markus PüschelCarnegie MellonSignalsKernel → ProcessProcess → Process (using kill)32 types of signalsSent by updating bit in pending vectorYou can write your own signal handlersID Name Default Action Corresponding Event2 SIGINT Terminate Interrupt (e.g., ctl-c from keyboard)9 SIGKILL Terminate Kill program (cannot override or ignore)11 SIGSEGV Terminate & Dump Segmentation violation14 SIGALRM Terminate Timer signal17 SIGCHLD Ignore Child stopped or terminatedCarnegie MellonSignal Handlers as Concurrent FlowsSignal deliveredSignal receivedProcess A Process Buser code (main)kernel codeuser code (main)kernel codeuser code (handler)context switchcontext switchkernel codeuser code (main)IcurrInextCarnegie MellonTodayMore on signalsLong jumpsVirtual memory (VM)Overview and motivationVM as tool for cachingVM as tool for memory managementVM as tool for memory protectionAddress translationCarnegie MellonSending Signals from the KeyboardTyping ctrl-c (ctrl-z) sends a SIGINT (SIGTSTP) to every job in the foreground process group.SIGINT – default action is to terminate each process SIGTSTP – default action is to stop (suspend) each processFore-groundjobBack-groundjob #1Back-groundjob #2ShellChild Childpid=10pgid=10Foreground process group 20Backgroundprocess group 32Backgroundprocess group 40pid=20pgid=20pid=32pgid=32pid=40pgid=40pid=21pgid=20pid=22pgid=20Carnegie MellonExample of ctrl-c and ctrl-zbluefish> ./forks 17Child: pid=28108 pgrp=28107Parent: pid=28107 pgrp=28107<types ctrl-z>Suspendedbluefish> ps w PID TTY STAT TIME COMMAND27699 pts/8 Ss 0:00 -tcsh28107 pts/8 T 0:01 ./forks 1728108 pts/8 T 0:01 ./forks 1728109 pts/8 R+ 0:00 ps wbluefish> fg./forks 17<types ctrl-c>bluefish> ps w PID TTY STAT TIME COMMAND27699 pts/8 Ss 0:00 -tcsh28110 pts/8 R+ 0:00 ps wSTAT (process state) Legend:First letter:S: sleepingT: stoppedR: runningSecond letter:s: session leader+: foreground proc groupSee “man ps” for more detailsCarnegie MellonSignal Handler FunkinessPending signals are not queuedFor each signal type, just have single bit indicating whether or not signal is pendingEven if multiple processes have sent this signalint ccount = 0;void child_handler(int sig){ int child_status; pid_t pid = wait(&child_status); ccount--; 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()) == 0) { sleep(1); /* deschedule child */ exit(0); /* Child: Exit */} while (ccount > 0)pause(); /* Suspend until signal occurs */}Carnegie MellonLiving With Nonqueuing SignalsMust check for all terminated jobsTypically loop with waitvoid child_handler2(int sig){ int child_status; pid_t pid; while ((pid = waitpid(-1, &child_status, WNOHANG)) > 0) {ccount--;printf("Received signal %d from process %d\n", sig, pid); }}void fork15(){ . . . signal(SIGCHLD, child_handler2); . . .}Carnegie MellonSignal Handler Funkiness (Cont.)Signal arrival during long system calls (say a read)Signal handler interrupts read() callLinux: upon return from signal handler, the read() call is restarted automaticallySome other flavors of Unix can cause the read() call to fail with an EINTER error number (errno)in this case, the application program can restart the slow system callSubtle differences like these complicate the writing of portable code that uses signalsCarnegie MellonA Program That Reacts toExternally Generated Events (Ctrl-c)#include <stdlib.h> #include <stdio.h> #include <signal.h> void handler(int sig) { printf("You think hitting ctrl-c will stop the bomb?\n"); sleep(2); printf("Well..."); fflush(stdout); sleep(1); printf("OK\n"); exit(0); } main() { signal(SIGINT, handler); /* installs ctrl-c handler */ while(1) { } }Carnegie MellonA Program That Reacts to Internally Generated Events#include <stdio.h> #include <signal.h> int beeps = 0; /* SIGALRM handler */void handler(int sig) { printf("BEEP\n"); fflush(stdout); if (++beeps < 5) alarm(1); else { printf("BOOM!\n"); exit(0); } } linux> a.out <What happens??>main() { signal(SIGALRM, handler); alarm(1); /* send SIGALRM to process in 1 second */ while (1) { /* handler returns here */ } }Carnegie MellonA Program That Reacts to Internally Generated Events#include <stdio.h> #include <signal.h> int beeps = 0; /* SIGALRM handler */void handler(int sig) { printf("BEEP\n"); fflush(stdout); if (++beeps < 5) alarm(1); else { printf("BOOM!\n"); exit(0); } } main() { signal(SIGALRM, handler); alarm(1); /* send SIGALRM to process in 1 second */ while (1) { /* handler returns here */ } } linux> a.out BEEP BEEP BEEP BEEP BEEP BOOM! bass>Carnegie MellonSummarySignals provide process-level exception handlingCan generate from user programsCan define effect by


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CMU CS 15213 - 16-virtual-memory

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