C: Linux C 编程 - 信号处理

信号

 

$ kill -l

 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL

 5) SIGTRAP 6) SIGABRT 7) SIGEMT 8) SIGFPE

 9) SIGKILL10) SIGBUS11) SIGSEGV12) SIGSYS

13) SIGPIPE14) SIGALRM15) SIGTERM16) SIGURG

17) SIGSTOP18) SIGTSTP19) SIGCONT20) SIGCHLD

21) SIGTTIN22) SIGTTOU23) SIGIO24) SIGXCPU

25) SIGXFSZ26) SIGVTALRM27) SIGPROF28) SIGWINCH

 

29) SIGINFO30) SIGUSR131) SIGUSR2

 

 

写道

signal - overview of signals
https://man7.org/linux/man-pages/man7/signal.7.html

注意是signal(7)，不是signal(2)。也不是linux.die.net提供的Manual。

 

/* Signals.  */
#define	SIGHUP		1	/* Hangup (POSIX).  */
#define	SIGINT		2	/* Interrupt (ANSI).  */
#define	SIGQUIT		3	/* Quit (POSIX).  */
#define	SIGILL		4	/* Illegal instruction (ANSI).  */
#define	SIGTRAP		5	/* Trace trap (POSIX).  */
#define	SIGABRT		6	/* Abort (ANSI).  */
#define	SIGIOT		6	/* IOT trap (4.2 BSD).  */
#define	SIGBUS		7	/* BUS error (4.2 BSD).  */
#define	SIGFPE		8	/* Floating-point exception (ANSI).  */
#define	SIGKILL		9	/* Kill, unblockable (POSIX).  */
#define	SIGUSR1		10	/* User-defined signal 1 (POSIX).  */
#define	SIGSEGV		11	/* Segmentation violation (ANSI).  */
#define	SIGUSR2		12	/* User-defined signal 2 (POSIX).  */
#define	SIGPIPE		13	/* Broken pipe (POSIX).  */
#define	SIGALRM		14	/* Alarm clock (POSIX).  */
#define	SIGTERM		15	/* Termination (ANSI).  */
#define	SIGSTKFLT	16	/* Stack fault.  */
#define	SIGCLD		SIGCHLD	/* Same as SIGCHLD (System V).  */
#define	SIGCHLD		17	/* Child status has changed (POSIX).  */
#define	SIGCONT		18	/* Continue (POSIX).  */
#define	SIGSTOP		19	/* Stop, unblockable (POSIX).  */
#define	SIGTSTP		20	/* Keyboard stop (POSIX).  */
#define	SIGTTIN		21	/* Background read from tty (POSIX).  */
#define	SIGTTOU		22	/* Background write to tty (POSIX).  */
#define	SIGURG		23	/* Urgent condition on socket (4.2 BSD).  */
#define	SIGXCPU		24	/* CPU limit exceeded (4.2 BSD).  */
#define	SIGXFSZ		25	/* File size limit exceeded (4.2 BSD).  */
#define	SIGVTALRM	26	/* Virtual alarm clock (4.2 BSD).  */
#define	SIGPROF		27	/* Profiling alarm clock (4.2 BSD).  */
#define	SIGWINCH	28	/* Window size change (4.3 BSD, Sun).  */
#define	SIGPOLL		SIGIO	/* Pollable event occurred (System V).  */
#define	SIGIO		29	/* I/O now possible (4.2 BSD).  */
#define	SIGPWR		30	/* Power failure restart (System V).  */
#define SIGSYS		31	/* Bad system call.  */
#define SIGUNUSED	31

#define	_NSIG		65	/* Biggest signal number + 1
				   (including real-time signals).  */

 

SIGPOLL

 

SIGIO

linux下SIGIO和SIGPOLL是同一种信号。要收到SIGIO或SIGPOLL信号，需要调用fcntl函数对相应的fd执行操作，指定F_SETOWN并指定参数为需要收到此信号的进程或进程组id。

 

这样进程还不能收到SIGIO或SIGPOLL信号，还需要调用fcntl函数对相应的fd执行操作，指定F_SETFL，将fd设置为异步模式，O_ASYNC，这样当此fd产生事件时，将会触发SIGIO或SIGPOLL信号，否则信号将被默默丢弃。

 

#include <stdio.h>
#include <signal.h>
#include <fcntl.h>
#include <unistd.h>

int i;

void on_signal_io(int sig)
{
  printf("signal: num=SIGIO(%d), %d\n", sig, i++);
}

int main()
{
  int oflags;

  signal(SIGIO, on_signal_io);

  oflags = fcntl(STDIN_FILENO, F_GETFL);
  fcntl(STDIN_FILENO, F_SETFL, oflags | O_ASYNC); // O_ASYNC, FASYNC

  fcntl(STDIN_FILENO, F_SETOWN, getpid());

  while (1)
  {
    
  }

  return 0;
}

 

 

参考poll和select函数。我们完全可以通过这个信号来自己实现poll和select的事件机制。至于能否实现epoll那样的事件机制，没有去验证，估计不行，毕竟epoll这种机制是由内核实现的。像epoll的事件触发机制，首先边缘触发和水平触发就可能无法实现。

 

信号处理

sighandler_t

类型定义

typedef void (*sighandler_t)(int);

 

signal

函数原型

sighandler_t signal(int signum, sighandler_t handler);

写道

The behavior of signal() varies across UNIX versions, and has also varied historically across different versions of Linux. Avoid its use: use sigaction(2) instead. See Portability below.

signal()的行为因UNIX版本而不同，而且在历史上也因Linux的不同版本而不同。避免其使用：使用sigaction()代替。请参阅下面的可移植性。

 

sigaction

函数原型

int sigaction(int signum, const struct sigaction *act, struct sigaction *oldact);

 

信号堆栈上下文

signal stack context，即信号堆栈上下文

 

typedef struct {
  void  *ss_sp;     /* Base address of stack */
  int    ss_flags;  /* Flags */
  size_t ss_size;   /* Number of bytes in stack */
} stack_t;

 

sigaltstack

sigaltstack - set and/or get signal stack context

函数原型

int sigaltstack(const stack_t *ss, stack_t *oss);

 

备用信号堆栈

alternate signal stack, 即备用信号堆栈

 

用户上下文

user context，即用户上下文

 

getcontext, setcontext - get or set the user context

 

getcontext

函数原型

int getcontext(ucontext_t *ucp);

 

setcontext

函数原型

int setcontext(const ucontext_t *ucp);

 

signal

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

void do_exit()
{  
  printf("exit.\n");
  exit(0);
}

void on_signal_int(int sig)
{
  printf("signal: num=SIGINT(%d)\n", sig);
  do_exit();
}

void on_signal_term(int sig)
{
  printf("signal: num=SIGTERM(%d)\n", sig);
  do_exit();
}

void on_signal_kill(int sig)
{
  printf("signal: num=SIGKILL(%d)\n", sig);
  do_exit();
}

int main(int argc, char** argv)
{
  // SIGINT signal
  signal(SIGINT, on_signal_int);
  signal(SIGTERM, on_signal_term);
  
  // The signals SIGKILL and SIGSTOP cannot be caught or ignored.
  // signal(SIGKILL, on_signal_kill);  

  while (1)
  {
    
  }

  return 0;
}

sigaction

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

void do_exit()
{  
  printf("exit.\n");
  exit(0);
}

void on_signal_int_action(int signal, siginfo_t *info, void *ucontext)
{
  printf("signal: num=SIGINT(%d)\n", signal);
  do_exit();
}

void on_signal_term_action(int signal, siginfo_t *info, void *ucontext)
{
  printf("signal: num=SIGTERM(%d)\n", signal);
  do_exit();
}

void on_signal_kill_action(int signal, siginfo_t *info, void *ucontext)
{
  printf("signal: num=SIGKILL(%d)\n", signal);
  do_exit();
}

int main(int argc, char** argv)
{
  struct sigaction on_signal_int, on_signal_term/*, on_signal_kill*/;

  on_signal_int.sa_sigaction = on_signal_int_action;
  on_signal_int.sa_flags = SA_SIGINFO;

  on_signal_term.sa_sigaction = on_signal_term_action;
  on_signal_term.sa_flags = SA_SIGINFO;

  // SIGINT signal
  sigaction(SIGINT, &on_signal_int, NULL);
  // SIGTERM signal
  sigaction(SIGTERM, &on_signal_term, NULL);
  
  // The signals SIGKILL and SIGSTOP cannot be caught or ignored.
  // SIGKILL signal
  // sigaction(SIGKILL, &on_signal_kill, NULL);  

  while (1)
  {
    
  }

  return 0;
}

 

向信号处理函数传递参数

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <ucontext.h>

void do_exit(int exit_code)
{  
  printf("exit.\n");
  exit(exit_code);
}

int ucstoi(stack_t stack)
{
  return *((int *) stack.ss_sp);
}

void on_signal_int_action(int signal, siginfo_t *info, void *ucontext)
{
  ucontext_t *p = (ucontext_t *) ucontext;
  int exit = ucstoi(p->uc_stack);
  printf("signal: num=SIGINT(%d), exit=%d\n", signal, exit);
  do_exit(exit);
}

void on_signal_term_action(int signal, siginfo_t *info, void *ucontext)
{
  ucontext_t *p = (ucontext_t *) ucontext;
  int exit = ucstoi(p->uc_stack);
  printf("signal: num=SIGTERM(%d), exit=%d\n", signal, exit);
  do_exit(exit);
}

void on_signal_kill_action(int signal, siginfo_t *info, void *ucontext)
{
  ucontext_t *p = (ucontext_t *) ucontext;
  int exit = ucstoi(p->uc_stack);
  printf("signal: num=SIGKILL(%d), exit=%d\n", signal, exit);
  do_exit(exit);
}

int createcontext(int arg)
{
  stack_t stack;
  ucontext_t ucontext;

  stack.ss_size = SIGSTKSZ;
  stack.ss_sp = malloc(stack.ss_size);
  stack.ss_flags = 0;

  memcpy(stack.ss_sp, &arg, sizeof(arg));

  if (sigaltstack(&stack, NULL) == -1)
  {
    printf("sig alt stack err.\n");
    return 1;
  }

  ucontext.uc_link = NULL;
  ucontext.uc_stack = stack;
  if (getcontext(&ucontext) == -1) 
  {
    printf("get context err.\n");
    return 1;
  }
  return 0;
}

int main(int argc, char** argv)
{
  struct sigaction on_signal_int, on_signal_term/*, on_signal_kill*/;

  on_signal_int.sa_sigaction = on_signal_int_action;
  on_signal_int.sa_flags = SA_SIGINFO;

  on_signal_term.sa_sigaction = on_signal_term_action;
  on_signal_term.sa_flags = SA_SIGINFO;

  int i = -1;
  if (argc == 2) 
  {
    i = atoi(argv[1]);
  }
  if (createcontext(i))
  {
    printf("create context err.\n");
    return 1;
  }

  // SIGINT signal
  sigaction(SIGINT, &on_signal_int, NULL);
  // SIGTERM signal
  sigaction(SIGTERM, &on_signal_term, NULL);
  
  // The signals SIGKILL and SIGSTOP cannot be caught or ignored.
  // SIGKILL signal
  // sigaction(SIGKILL, &on_signal_kill, NULL);  

  while (1)
  {
    
  }

  return 0;
}