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subr_once.c revision 1.4 
      1 /*	$NetBSD: subr_once.c,v 1.4 2008/10/09 10:48:21 pooka 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 1.4 2008/10/09 10:48:21 pooka Exp $");
     32 
     33 #include <sys/param.h>
     34 #include <sys/systm.h>
     35 #include <sys/atomic.h>
     36 #include <sys/condvar.h>
     37 #include <sys/mutex.h>
     38 #include <sys/once.h>
     39 
     40 static kmutex_t oncemtx;
     41 static kcondvar_t oncecv;
     42 
     43 void
     44 once_init()
     45 {
     46 
     47 	mutex_init(&oncemtx, MUTEX_DEFAULT, IPL_NONE);
     48 	cv_init(&oncecv, "runonce");
     49 }
     50 
     51 int
     52 _run_once(once_t *o, int (*fn)(void))
     53 {
     54 
     55 	/* Fastpath handled also by RUN_ONCE(), but be pedantic */
     56 	if (o->o_status == ONCE_DONE)
     57 		goto out;
     58 
     59 	mutex_enter(&oncemtx);
     60 	if (o->o_status == ONCE_VIRGIN) {
     61 		atomic_swap_uint(&o->o_status, ONCE_RUNNING);
     62 		mutex_exit(&oncemtx);
     63 		o->o_error = fn();
     64 		atomic_swap_uint(&o->o_status, ONCE_DONE);
     65 		mutex_enter(&oncemtx);
     66 		cv_broadcast(&oncecv);
     67 	}
     68 	while (o->o_status == ONCE_RUNNING)
     69 		cv_wait(&oncecv, &oncemtx);
     70 	mutex_exit(&oncemtx);
     71 
     72  out:
     73 	KASSERT(o->o_status == ONCE_DONE);
     74 	return o->o_error;
     75 }
     76