#include <u.h>#include <libc.h> #define	NEXIT	33 typedef struct Onex Onex;struct Onex{	void	(*f)(void);	int	pid;}; static Lock onexlock;Onex onex[NEXIT]; intatexit(void (*f)(void)){	int i; 	lock(&onexlock);	for(i=0; i<NEXIT; i++)		if(onex[i].f == 0) {			onex[i].pid = getpid();			onex[i].f = f;			unlock(&onexlock);			return 1;		}	unlock(&onexlock);	return 0;} voidexits(char *s){	int i, pid;	void (*f)(void); 	pid = getpid();	for(i = NEXIT-1; i >= 0; i--)		if((f = onex[i].f) && pid == onex[i].pid) {			onex[i].f = 0;			(*f)();		}	exit(s && *s);}