ref: 261ec9fe0e0b2dbde909da79a93e90220a9ea62c
dir: /sys/src/libc/port/atexit.c/
#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];
int
atexit(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;
}
void
atexitdont(void (*f)(void))
{
	int i, pid;
	pid = getpid();
	for(i=0; i<NEXIT; i++)
		if(onex[i].f == f && onex[i].pid == pid)
			onex[i].f = 0;
}
#pragma profile off
void
exits(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)();
		}
	_exits(s);
}
#pragma profile on