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      1 /*	$NetBSD: subr_once.c,v 1.7 2019/03/19 08:16:51 ryo Exp $	*/
      2 
      3 /*-
      4  * Copyright (c)2005 YAMAMOTO Takashi,
      5  * Copyright (c)2008 Antti Kantee,
      6  * All rights reserved.
      7  *
      8  * Redistribution and use in source and binary forms, with or without
      9  * modification, are permitted provided that the following conditions
     10  * are met:
     11  * 1. Redistributions of source code must retain the above copyright
     12  *    notice, this list of conditions and the following disclaimer.
     13  * 2. Redistributions in binary form must reproduce the above copyright
     14  *    notice, this list of conditions and the following disclaimer in the
     15  *    documentation and/or other materials provided with the distribution.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     27  * SUCH DAMAGE.
     28  */
     29 
     30 #include <sys/cdefs.h>
     31 __KERNEL_RCSID(0, "$NetBSD: subr_once.c,v 1.7 2019/03/19 08:16:51 ryo Exp $");
     32 
     33 #include <sys/param.h>
     34 #include <sys/systm.h>
     35 #include <sys/condvar.h>
     36 #include <sys/mutex.h>
     37 #include <sys/once.h>
     38 
     39 static kmutex_t oncemtx;
     40 static kcondvar_t oncecv;
     41 
     42 void
     43 once_init(void)
     44 {
     45 
     46 	mutex_init(&oncemtx, MUTEX_DEFAULT, IPL_NONE);
     47 	cv_init(&oncecv, "runonce");
     48 }
     49 
     50 int
     51 _init_once(once_t *o, int (*fn)(void))
     52 {
     53 	/* Fastpath handled by RUN_ONCE() */
     54 
     55 	int error;
     56 
     57 	mutex_enter(&oncemtx);
     58 	while (o->o_status == ONCE_RUNNING)
     59 		cv_wait(&oncecv, &oncemtx);
     60 
     61 	if (o->o_refcnt++ == 0) {
     62 		o->o_status = ONCE_RUNNING;
     63 		mutex_exit(&oncemtx);
     64 		o->o_error = fn();
     65 		mutex_enter(&oncemtx);
     66 		o->o_status = ONCE_DONE;
     67 		cv_broadcast(&oncecv);
     68 	}
     69 	KASSERT(o->o_refcnt != 0);	/* detect overflow */
     70 
     71 	while (o->o_status == ONCE_RUNNING)
     72 		cv_wait(&oncecv, &oncemtx);
     73 	error = o->o_error;
     74 	mutex_exit(&oncemtx);
     75 
     76 	return error;
     77 }
     78 
     79 void
     80 _fini_once(once_t *o, void (*fn)(void))
     81 {
     82 	mutex_enter(&oncemtx);
     83 	while (o->o_status == ONCE_RUNNING)
     84 		cv_wait(&oncecv, &oncemtx);
     85 
     86 	KASSERT(o->o_refcnt != 0);	/* we need to call _init_once() once */
     87 	if (--o->o_refcnt == 0) {
     88 		o->o_status = ONCE_RUNNING;
     89 		mutex_exit(&oncemtx);
     90 		fn();
     91 		mutex_enter(&oncemtx);
     92 		o->o_status = ONCE_VIRGIN;
     93 		cv_broadcast(&oncecv);
     94 	}
     95 
     96 	mutex_exit(&oncemtx);
     97 }
     98