1 / 26

Linux/UNIX Programming APUE (Signals )

Linux/UNIX Programming APUE (Signals ). Signals. APUE (Signals). Signals are software interrupts( 가로채기 ) an illegal operation (e.g., divide by 0 ) an alarm clock the death of a child process a termination request from a user a suspend request from a user. Process. Signal ##.

kenton
Télécharger la présentation

Linux/UNIX Programming APUE (Signals )

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Linux/UNIX Programming APUE (Signals)

  2. Signals APUE (Signals) • Signals are software interrupts(가로채기) • an illegal operation (e.g., divide by 0) • an alarm clock • the death of a child process • a termination request from a user • a suspend request from a user Process Signal ##

  3. Predefined Signals (1/2) APUE (Signals) • define • /usr/include/signal.h(/usr/include/sys/iso/signal_iso.h) • Every signal has a name • begin with ‘SIG’ • SIGABRT: abort signal from abort() • SIGALRM: alarm signal from alarm() • Actions of the default signal handler • terminate the process and generate a core(dump) • ignores and discards the signal(ignore) • suspends the process (suspend) • resume the process

  4. Predefined Signals (2/2) APUE (Signals) /usr/include/asm/signal.h

  5. Signal Generation APUE (Signals) • Terminal-generated signals • CTRL-C  SIGINT • CTRL-Z  SIGSTP signal • Hardware excepts generate signals • divide by 0  SIGFPE • invalid memory reference  SIGSEGV • kill() • sends any signal to a process or process group • need to be owner or super-user • Software conditions • SIGALRM: alarm clock expires • SIGPIPE: broken pipe • SIGURG: out-of-band network data

  6. Handling of Signals APUE (Signals) Ignore the signal:모든 시그널은 무시할 수 있음, 단SIGKILL and SIGSTOP은 예외 signal catching function:시그널 발생시 호출될 함수를 지정할 수 있음 Let the default action apply:most are to terminate process

  7. Representative UNIX Signals (1/2) APUE (Signals) SIGART : 비정상 종료(종료+코어덤프) SIGALRM : 타이머 만료(종료) SIGCHLD : 자식의 상태 변화(무시) SIGCONT : 중단된 프로세스의 실행 재개(재개/무시) SIGFPE : 산술예외, such as divide-by-0 (종료+코어덤프) SIGILL :적법하지 않은 명령(종료+코어덤프) SIGINT: 터미널 가로채기(종료)

  8. Representative UNIX Signals (2/2) APUE (Signals) SIGKILL : 종료, 무시할수 없음(종료) SIGPIPE : 리더가 없는 파이프 쓰기(종료) SIGSEGV : 유효하지 않은 메모리 참조(종료+코어덤프) SIGTERM : 종료(종료) SIGSTOP : 중단(프로세스 중단) SIGUSR1 : user defined signal 1(종료) SIGUSR2 : user defined signal 2(종료)

  9. signal() APUE (Signals) • Signal Handler 등록 • signal(int signo, void(*func)())) • specify the action for a signal (signo  func) • func • SIG_IGN (ignore) • SIG_DFL (default) • user-defined function • Return: the previous func

  10. 예제: alarm1.c (w/o handler) APUE (Signals) #include <stdio.h> // alarm1.c main( ) { alarm(3); printf(“Looping forever …\n”); while (1); printf(“This line should never be executed\n”); }

  11. 예제: alarm2.c (w/ handler) (1/2) APUE (Signals) #include <stdio.h> // alarm2.c #include <signal.h> intalarmFlag=0; void alarmHandler(); main( ) { signal(SIGALRM, alarmHandler); alarm(3); printf("Looping …\n"); while(!alarmFlag) { pause( ); } printf("Loop ends due to alarm signal \n"); } void alarmHandler( ) { printf("An alarm clock signal was received\n"); alarmFlag = 1; }

  12. 예제: alarm2.c (w/ handler) (2/2) APUE (Signals) 실행 결과

  13. SIGCHLD APUE (Signals) Whenever a process terminates or stops, the signal is sent to the parent. 자식 프로세스는 자신이 죽을 때, 부모 프로세스에게 SIGCHLD를 보낸다.

  14. 예제: timelimit.c (1/3) APUE (Signals) $ timelimit N command// command를 N seconds안에 수행하라! #include <stdio.h> // timelimit.c #include <signal.h> int delay; void childHandler( ); main(intargc, char *argv[]) { intpid; sscanf(argv[1], "%d", &delay); signal(SIGCHLD,childHandler); pid = fork(); if (pid == 0) { // child execvp(argv[2], &argv[2]); perror("Limit"); } else { // parent sleep(delay); printf("Child %d exceeded limit and is being killed\n", pid); kill(pid, SIGINT); } }

  15. 예제: timelimit.c (2/3) APUE (Signals) childHandler( ) /* Executed if the child dies before the parent */ { intchildPid, childStatus; childPid = wait(&childStatus); printf(“Child %d terminated within %d seconds\n”, childPid, delay); exit(0); }

  16. 예제: timelimit.c (3/3) APUE (Signals) 실행 결과

  17. kill(), raise() APUE (Signals) #include <sys/types.h> #include <signal.h> int kill(pid_tpid, intsigno); int raise(intsigno); Both return: 0 if OK, 1 on error • kill - sends a signal to a process or a group of processes • raise - function allows a process to send a signal to itself • raise(signo) == kill(getpid(), signo);

  18. kill() APUE (Signals) • pid means • pid > 0 : 프로세스 ID가 pid인 프로세스에 신호를 보낸다. • pid == 0 : 프로세스 그룹 ID가 동일한 모든 프로세스에게 신호를 보낸다. • pid < 0 : 프로세스 그룹 ID가 pid인 모든 프로세스에게 신호를 보낸다. • pid == -1 : 모든 프로세스에 신호를 보낸다.(boradcast) • Permission to send signals • The super-user can send a signal to any process. • The real or effective user ID of the sender has to equal the real or effective user ID of the receiver.

  19. alarm() APUE (Signals) #include <unistd.h> unsigned int alarm (unsigned int seconds); Returns: 0 or number of seconds until previously set alarm • alarm() 는 지정된 시간 이후에 만료될 타이머를 설정하는데 사용 • when timer expires, SIGALRM signal is generated, • default action of the signal is to terminate the process. • Only one alarm clock per process • 이전에 설정한 타이머가 만료되지 않은 상황에서 alarm을 호출하면 타이머는 새로운 값으로 설정됨 • if alarm(0), a previous unexpired alarm is cancelled.

  20. pause() APUE (Signals) #include <unistd.h> int pause (void); Returns: -1 with errno set to EINTR • 신호가 전달될 때까지 프로세스를 일시정지 시킴 • Signal handler의 실행이 끝날 때까지 차단된다. • signal handler가 등록된 경우 해당 handler가 처리를 마친 후 리턴한다.

  21. 예제: mysleep.c (1/2) APUE (Signals) #include <signal.h> // mysleep.c #include <unistd.h> static void sig_alrm(intsigno) { return; /* nothing to do, just return to wake up the pause */ } unsigned intmysleep(unsigned intnsecs) { if (signal(SIGALRM, sig_alrm) == SIG_ERR) return nsecs; alarm(nsecs); /* start the timer */ pause(); /* next caught signal wakes us up */ return alarm(0); /* turn off timer, return unslept time */ } • 상기 mysleep() 함수는 다음과 같은 몇 가지 문제점을 안고 있다. • 만일 mysleep()을 사용하기 이전에 alarm을 set한 경우, 앞서의 alarm이 지워진다. • Race condition이 발생할 수 있다(즉, pause()가 호출되기 전에 alarm이 발생할 수 있다.). • 상기 문제 해결을 위해서는 보다 견고한 mysleep()의 구현이 필요하다.

  22. 예제: mysleep.c (2/2) APUE (Signals)

  23. abort() APUE (Signals) #include <stdlib.h> void abort(void); This function never returns • abnormal program termination. • This function sends the SIGABRT signal to the process. • raise(SIGABRT) • SIGABRT signal handler to perform any cleanup that it wants to do, before the process terminated.

  24. sleep() APUE (Signals) #include <signal.h> unsigned int sleep(unsigned int seconds) ; Returns: 0 or number of unslept seconds • 호출한 프로세스를 일시 정시 상태로 만듬, 아래 두가지조건중 하나가 발생하면 깨어남 • 타이머가 만료 된 경우 • 프로세스가 신호를 잡았으며 해당 신호 처리부가 반환 될 경우

  25. sigaction() APUE (Signals) #include <signal.h> intsigaction(int sig, structsigaction * act, structsigaction * act) ; return: 0 if OK, 1 on error • sigaction구조체를 사용해 핸들러를 등록 strcutsigaction { void (* sa_handler)(int) //핸들러 sigset_tsa_mask //차단할 신호들 intsa_flags; //옵션들 }

  26. sigaction() APUE (Signals) #include <signal.h> #include <stdio.h> #include <unistd.h> void ouch(int sig) { print(“OUCH! – I got signal %d\n”, sig); int main() { structsigaction act; act.sa_handler = ouch; sigemptyset(&act.sa_mask); act.sa_flags = 0; sigaction(SIGINT, &act, 0); wihle(1) { printf(“hello world\n”); sleep(1); } }

More Related