signal.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include "lib.h"
#include "sys9.h"
#include <signal.h>
#include <errno.h>
#include <string.h>
#include <setjmp.h>

extern sigset_t	_psigblocked;

static struct {
	char	*msg;	/* just check prefix */
	int	num;
} sigtab[] = {
	{"hangup",				SIGHUP},
	{"interrupt",				SIGINT},
	{"quit",				SIGQUIT},
	{"alarm",				SIGALRM},
	{"sys: trap: illegal instruction",	SIGILL},
	{"sys: trap: reserved instruction",	SIGILL},
	{"sys: trap: reserved",			SIGILL},
	{"sys: trap: arithmetic overflow",	SIGFPE},
	{"abort",				SIGABRT},
	{"sys: fp:",				SIGFPE},
	{"exit",				SIGKILL},
	{"die",					SIGKILL},
	{"kill",				SIGKILL},
	{"sys: trap: bus error",		SIGSEGV},
	{"sys: trap: address error",		SIGSEGV},
	{"sys: trap: TLB",			SIGSEGV},
	{"sys: write on closed pipe",		SIGPIPE},
	{"alarm",				SIGALRM},
	{"term",				SIGTERM},
	{"usr1",				SIGUSR1},
	{"usr2",				SIGUSR2},
};
#define NSIGTAB ((sizeof sigtab)/(sizeof (sigtab[0])))

void	(*_sighdlr[MAXSIG+1])(int, char*, Ureg*); /* 0 initialized: SIG_DFL */

void
(*signal(int sig, void (*func)(int, char*, Ureg*)))(int, char*, Ureg*)
{
	void(*oldf)(int, char*, Ureg*);

	if(sig <= 0 || sig > MAXSIG){
		errno = EINVAL;
		return SIG_ERR;
	}
	oldf = _sighdlr[sig];
	if(sig == SIGKILL)
		return oldf;	/* can't catch or ignore SIGKILL */
	_sighdlr[sig] = func;
	return oldf;
}

/* BAD CODE - see /sys/src/ape/lib/ap/$objtype/setjmp.s for real code
int
sigsetjmp(sigjmp_buf buf, int savemask)
{
	int r;

	buf[0] = savemask;
	buf[1] = _psigblocked;
	return setjmp(&buf[2]);
}
*/

/*
 * BUG: improper handling of process signal mask
 */
int
sigaction(int sig, struct sigaction *act, struct sigaction *oact)
{
	if(sig <= 0 || sig > MAXSIG || sig == SIGKILL){
		errno = EINVAL;
		return -1;
	}
	if(oact){
		oact->sa_handler = _sighdlr[sig];
		oact->sa_mask = _psigblocked;
		oact->sa_flags = 0;
	}
	if(act){
		_sighdlr[sig] = act->sa_handler;
	}
	return 0;
}

/* this is registered in _envsetup */
int
_notehandler(Ureg *u, char *msg)
{
	int i;
	void(*f)(int, char*, Ureg*);
	extern void _doatexits(void);	/* in stdio/exit.c */

	if(_finishing)
		_finish(0, 0);
	for(i = 0; i<NSIGTAB; i++){
		if(strncmp(msg, sigtab[i].msg, strlen(sigtab[i].msg)) == 0){
			f = _sighdlr[sigtab[i].num];
			if(f == SIG_DFL || f == SIG_ERR)
				break;
			if(f != SIG_IGN) {
				_notetramp(sigtab[i].num, f, u);
				/* notetramp is machine-dependent; doesn't return to here */
			}
			_NOTED(0); /* NCONT */
			return;
		}
	}
	_doatexits();
	_NOTED(1); /* NDFLT */
}

int
_stringsig(char *nam)
{
	int i;

	for(i = 0; i<NSIGTAB; i++)
		if(strncmp(nam, sigtab[i].msg, strlen(sigtab[i].msg)) == 0)
			return sigtab[i].num;
	return 0;
}

char *
_sigstring(int sig)
{
	int i;

	for(i=0; i<NSIGTAB; i++)
		if(sigtab[i].num == sig)
			return sigtab[i].msg;
	return "unknown signal";
}