Lecture 16 Signals

1
Lecture 16Signals
CSCE 510 Systems Programming

• Topics
• Shell operations
• Shell implementation
• Redirecting I/O

October 11, 2005
2

• Last Time
• Multiple Pipes implementation
• Today
• Filename expansion implementation re_comp,
  re_exec
• Program 2

3
Signal Sets
4
Sigaction Table

• struct sigaction
• void (sa_handler) __(()) / signal handler, or
  action value /
• sigset_t sa_mask / signals to block while in
  handler /
• int sa_flags / signal action flags /
• int sa_signo / signal number /

5

• include ltsignal.hgt
• int sigaction(int signum, const struct sigaction
  act, struct sigaction oldact)
• int sigprocmask(int how, const sigset_t set,
  sigset_t oldset)
• int sigpending(sigset_t set)
• int sigsuspend(const sigset_t mask)

6
Sigmask0.c

• include ltsetjmp.hgt
• include ltsignal.hgt
• main()
• sigset_t sigset, oldset
• sigemptyset(sigset)
• sigaddset(sigset, SIGINT)
• if(sigprocmask(SIG_SETMASK, sigset, oldset)
  lt 0)
• fprintf(stderr, "sigprocmask ERROR\n")
• exit(1)
• sleep(5)
• if(sigismember(sigset, SIGINT))
  printf("SIGINT MASKED\n")
• else printf("SIGINT NOT MASKED\n")

7
Sigmask1.c

• main()
• sigset_t sigset, oldset, newset
• int pid
• sigemptyset(sigset)
• sigaddset(sigset, SIGINT)
• if(sigprocmask(SIG_SETMASK, sigset, oldset)
  lt 0) fatal("sigprocmask")
• if((pid fork()) lt 0) fatal("Fork failed")
• else if (pid 0)
• sleep(3)
• if(sigpending(newset)lt 0)
  fatal("SIGpending")
• if(sigismember(newset,SIGINT))
• printf("SIGINT signal is pending\n")
• else
• if(kill(pid, SIGINT)lt 0) fatal("Fork
  failed") / sigsend on SUNs /

8
SigQueued.c
if((pid fork()) lt 0) fatal("Fork failed")
else if (pid 0) for(i0 i lt 100
i) sleep(1)
printf("Finished sleeping\n") else
for(inumSignals i gt 0 --i)
if(kill(pid, SIGUSR1)lt 0) fatal("Kill failed")
wait(NULL) void onintr(int sig)
fprintf(stderr,"Sig d Caught d times\n",
sig, countSigs)

• void onintr(int)
• int countSigs 0
• main(int argc, char argv)
• sigset_t sigset, oldset, newset
• int pid
• struct sigaction act, oact
• int i
• int numSignals
• if(argc ! 2) fatal("Usage sigtest num")
• numSignals atoi(argv1)
• act.sa_handler onintr
• sigaction(SIGUSR1, act, NULL)

9
Zombies and Fireman

• signal(SIGCHLD, fireman) / this eliminates
  zombies / .....
• / as children die we should get catch their
  returns or else we get zombies, A Bad Thing.
  fireman() catches falling children. /
• void fireman (int sig)
• int wstatus
• int pid
• while ((pidwaitpid(0,wstatus, WNOHANG)) gt 0)
  fprintf(stderr,"SIGCHLD child d returned
  d\n",pid, WEXITSTATUS(wstatus ))

10
SigSetjmp

• NAME
• setjmp, sigsetjmp - save stack context for
  non-local goto
• SYNOPSIS
• include ltsetjmp.hgt
• int setjmp(jmp_buf env)
• int sigsetjmp(sigjmp_buf env, int
  savesigs)
• If savesigs is nonzero, the set of blocked
  signals is saved in env and will be restored if a
  siglongjmp() is later performed with this env.