/*      $NetBSD: subr_once.c,v 1.7 2019/03/19 08:16:51 ryo Exp $        */

/*-
* Copyright (c)2005 YAMAMOTO Takashi,
* Copyright (c)2008 Antti Kantee,
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: subr_once.c,v 1.7 2019/03/19 08:16:51 ryo Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/condvar.h>
#include <sys/mutex.h>
#include <sys/once.h>

static kmutex_t oncemtx;
static kcondvar_t oncecv;

void
once_init(void)
{

       mutex_init(&oncemtx, MUTEX_DEFAULT, IPL_NONE);
       cv_init(&oncecv, "runonce");
}

int
_init_once(once_t *o, int (*fn)(void))
{
       /* Fastpath handled by RUN_ONCE() */

       int error;

       mutex_enter(&oncemtx);
       while (o->o_status == ONCE_RUNNING)
               cv_wait(&oncecv, &oncemtx);

       if (o->o_refcnt++ == 0) {
               o->o_status = ONCE_RUNNING;
               mutex_exit(&oncemtx);
               o->o_error = fn();
               mutex_enter(&oncemtx);
               o->o_status = ONCE_DONE;
               cv_broadcast(&oncecv);
       }
       KASSERT(o->o_refcnt != 0);      /* detect overflow */

       while (o->o_status == ONCE_RUNNING)
               cv_wait(&oncecv, &oncemtx);
       error = o->o_error;
       mutex_exit(&oncemtx);

       return error;
}

void
_fini_once(once_t *o, void (*fn)(void))
{
       mutex_enter(&oncemtx);
       while (o->o_status == ONCE_RUNNING)
               cv_wait(&oncecv, &oncemtx);

       KASSERT(o->o_refcnt != 0);      /* we need to call _init_once() once */
       if (--o->o_refcnt == 0) {
               o->o_status = ONCE_RUNNING;
               mutex_exit(&oncemtx);
               fn();
               mutex_enter(&oncemtx);
               o->o_status = ONCE_VIRGIN;
               cv_broadcast(&oncecv);
       }

       mutex_exit(&oncemtx);
}