_exit.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 <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>

int _finishing = 0;
int _sessleader = 0;

static char exitstatus[ERRMAX];

void
_exit(int status)
{
	_finish(status, 0);
}

void
_finish(int status, char *term)
{
	int i, nalive;
	char *cp;

	if(_finishing)
		_EXITS(exitstatus);
	_finishing = 1;
	if(status){
		cp = _ultoa(exitstatus, status & 0xFF);
		*cp = 0;
	}else if(term){
		strncpy(exitstatus, term, ERRMAX);
		exitstatus[ERRMAX-1] = '\0';
	}
	if(_sessleader)
		kill(0, SIGTERM);
	_EXITS(exitstatus);
}

/* emulate: return p+sprintf(p, "%uld", v) */
#define IDIGIT 15
char *
_ultoa(char *p, unsigned long v)
{
	char s[IDIGIT];
	int n, i;

	s[IDIGIT-1] = 0;
	for(i = IDIGIT-2; i; i--){
		n = v % 10;
		s[i] = n + '0';
		v = v / 10;
		if(v == 0)
			break;
	}
	strcpy(p, s+i);
	return p + (IDIGIT-1-i);
}