Chap04(Signals and Sessions).PDF

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1 Signals and Session Management Hyun-Ju Park

2 (Signal)? Introduction (1) mechanism events : asynchronous events - interrupt signal from users : synchronous events - exceptions (accessing an illegal address) primitive mechanism an integer value which specifies the type of events Signals and Session Management 1

3 History Introduction (2) Original System V signal unreliable and defective 4.2BSD reliable, robust signal SVR3 System V reliable signal (4.2BSD incompatible) POSIX BSD SVR3 reliable signal Solaris, AIX, HP-UX, 4.4BSD, Digital UNIX UNIX POSIX compliant signal Signals and Session Management 2

4 Issues Introduction (3)? ( ),???? Signals and Session Management 3

5 (generation) (delivery) Signal? Original system V defined 15 signals 4BSD and SVR4 define 32 signals (some variants support more than 32 signals) POSIX signal symbolic name 102, 4-1 Signals and Session Management 4

6 (1), function signal handler default action Signals and Session Management 5

7 (2) 5 default actions for signals abort : terminate the process after generating a core dump exit : terminates the process without generating a core dump ignore : ignores the signal stop : suspends the process continue : resumes the process, if suspended( or else, ignores the signal) User defined function(signal handler) SIGKILL SIGSTOP ignore, block, signal handler 102, 4-1 Signals and Session Management 6

8 (3) issig(), issig() issig() TRUE, psig() psig(): sendsig() Signals and Session Management 7

9 (4) Signal delivered Execute normal code Signal handler runs Resume normal execution Signals and Session Management 8

10 (1) Major sources of signals (exceptions) (terminal interrupts) (job control) (quotas) (notifications) (alarms) Signals and Session Management 9

11 (2) kill sigsend Ctrl-C foreground process csh ksh foreground background process Signals and Session Management 10

12 (3) CPU Signals and Session Management 11

13 (1) Asynchronous events Ctrl-C foreground process SIGINT, (issig()) Signals and Session Management 12

14 (2) Synchronous events : exception, issig() Signals and Session Management 13

15 Sleep and Signals What happens sleeping process receives a signal? Two categories of sleep uninterruptible sleep sleep : mark the signal as pending interruptible sleep : issig() Signals and Session Management 14

16 Signals in SVR4 (1) Superset of the functionality of SVR3 and BSD signals sigprocmask(int how, const sigset_t * setp, sigset_t *osetp); how: SIG_BLOCK, SIG_UNBLOCK, SIG_SETMASK setp: new mask osetp: old mask if not nonnull pointer sigaltstack(stack, old_stack); sigsuspend(const sigset_t* sigmask); unblocking pause signal atomic operation sigpending(sigset_t* setp); block or pending signal check sigsendset(procset_t* procset, sig); process group sig Signals and Session Management 15

17 Signals in SVR4 (2) sigaction(int signo, const struct sigaction* act, struct sigaction oact); struct sigaction { } void (*sa_handler) (); /* addr of signal handler, or SIG_IGN, or SIG_DFL*/ sigset_t sa_mask; /* additional signals to block */ int sa_flags; /* signal options */ sa_mask signo act signo Signals and Session Management 16

18 Signals in SVR4 (3) SVR4 signal implementation BSD u area : contains information required to properly invoke the signal handlers, u_signal[ ]: vector of signal handlers for each signal u_sigmask[ ]: signal masks associated with each handler u_sigaltstack: pointer to the alternate signal stack u_sigonstack: mask of signals to handle on the alternate stack u_oldsig: set of handlers that must exhibit the old, unreliable behavior proc structure : contains fields related to generation and posting of signals p_cursig: current signal being handled p_sig: pending signal mask p_hold: blocked signal mask p_ignore: ignored signal mask Signals and Session Management 17

19 #include <signal.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <unistd.h> void sigusr1_handler (int signal_number) { printf( Ctrl-C!!\n ); printf( --> \n ); exit(1); } int main (void) { struct sigaction sa; memset (&sa, 0, sizeof (sa)); sa.sa_handler =&sigint_handler; sigaction (SIGINT,&sa,NULL); while (1) printf( * ); printf ( \n ); return 0; } Signals and Session Management 18

20 UNIX, Signals and Session Management 19

21 (1) (Process groups) ID process group ID event PID ID, /dev/tty Signals and Session Management 20

22 (2) tty t_pgrp SIGINT, SIGQUIT fg (SIGCONT) Ctrl-Z (SIGTSTP) bg Signals and Session Management 21

23 SVR3 Process group is the same as a terminal login session P P P P P Process Foreground Process Proces group Login session Signals and Session Management 22

24 SVR4 Introduces a session structure Session = a collection of process groups P P P P P P Session Object P P Process Foreground Process Proces group Login session Signals and Session Management 23

제1장 Unix란 무엇인가?

제1장 Unix란 무엇인가? 1 시그널 2 11.1 시그널 시그널 시그널은예기치않은사건이발생할때이를알리는소프트웨어인터럽트이다. 시그널발생예 SIGFPE 부동소수점오류 SIGPWR 정전 SIGALRM 알람시계울림 SIGCHLD 자식프로세스종료 SIGINT 키보드로부터종료요청 (Ctrl-C) SIGSTP 키보드로부터정지요청 (Ctrl-Z) 3 주요시그널 시그널이름 의미 기본처리 SIGABRT