ref: c23736f35ed7a2cc1dcdbca7cd4d8418cad76d86
dir: /sys/src/libc/9sys/privalloc.c/
#include <u.h>
#include <libc.h>
static Lock	privlock;
extern void	**_privates;
extern int	_nprivates;
void **
privalloc(void)
{
	void **p;
	lock(&privlock);
	if(_nprivates > 0)
		p = &_privates[--_nprivates];
	else
		p = nil;
	unlock(&privlock);
	return p;
}