kern_sema.c revision 81645
181645Sjasone/* 281645Sjasone * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved. 381645Sjasone * 481645Sjasone * Redistribution and use in source and binary forms, with or without 581645Sjasone * modification, are permitted provided that the following conditions 681645Sjasone * are met: 781645Sjasone * 1. Redistributions of source code must retain the above copyright 881645Sjasone * notice(s), this list of conditions and the following disclaimer as 981645Sjasone * the first lines of this file unmodified other than the possible 1081645Sjasone * addition of one or more copyright notices. 1181645Sjasone * 2. Redistributions in binary form must reproduce the above copyright 1281645Sjasone * notice(s), this list of conditions and the following disclaimer in the 1381645Sjasone * documentation and/or other materials provided with the distribution. 1481645Sjasone * 1581645Sjasone * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 1681645Sjasone * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 1781645Sjasone * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 1881645Sjasone * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 1981645Sjasone * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 2081645Sjasone * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 2181645Sjasone * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 2281645Sjasone * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 2381645Sjasone * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 2481645Sjasone * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 2581645Sjasone * DAMAGE. 2681645Sjasone * 2781645Sjasone * $FreeBSD: head/sys/kern/kern_sema.c 81645 2001-08-14 22:13:14Z jasone $ 2881645Sjasone */ 2981645Sjasone 3081645Sjasone/* 3181645Sjasone * Counting semaphores. 3281645Sjasone * 3381645Sjasone * Priority propagation will not generally raise the priority of semaphore 3481645Sjasone * "owners" (a misnomer in the context of semaphores), so should not be relied 3581645Sjasone * upon in combination with semaphores. 3681645Sjasone */ 3781645Sjasone 3881645Sjasone#include <sys/param.h> 3981645Sjasone#include <sys/systm.h> 4081645Sjasone#include <sys/ktr.h> 4181645Sjasone#include <sys/condvar.h> 4281645Sjasone#include <sys/lock.h> 4381645Sjasone#include <sys/mutex.h> 4481645Sjasone#include <sys/sema.h> 4581645Sjasone 4681645Sjasonevoid 4781645Sjasonesema_init(struct sema *sema, int value, const char *description) 4881645Sjasone{ 4981645Sjasone 5081645Sjasone KASSERT((value >= 0), ("%s(): negative value\n", __func__)); 5181645Sjasone 5281645Sjasone bzero(sema, sizeof(*sema)); 5381645Sjasone mtx_init(&sema->sema_mtx, "sema backing lock", 5481645Sjasone MTX_DEF | MTX_NOWITNESS | MTX_QUIET); 5581645Sjasone cv_init(&sema->sema_cv, description); 5681645Sjasone sema->sema_value = value; 5781645Sjasone 5881645Sjasone CTR3(KTR_LOCK, __func__ "(%p, %d, \"%s\")", sema, value, description); 5981645Sjasone} 6081645Sjasone 6181645Sjasonevoid 6281645Sjasonesema_destroy(struct sema *sema) 6381645Sjasone{ 6481645Sjasone 6581645Sjasone CTR2(KTR_LOCK, __func__ "(%p) \"%s\"", sema, 6681645Sjasone cv_wmesg(&sema->sema_cv)); 6781645Sjasone 6881645Sjasone KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__)); 6981645Sjasone 7081645Sjasone mtx_destroy(&sema->sema_mtx); 7181645Sjasone cv_destroy(&sema->sema_cv); 7281645Sjasone} 7381645Sjasone 7481645Sjasonevoid 7581645Sjasone_sema_post(struct sema *sema, const char *file, int line) 7681645Sjasone{ 7781645Sjasone 7881645Sjasone mtx_lock(&sema->sema_mtx); 7981645Sjasone sema->sema_value++; 8081645Sjasone if (sema->sema_waiters && sema->sema_value > 0) 8181645Sjasone cv_signal(&sema->sema_cv); 8281645Sjasone 8381645Sjasone CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema, 8481645Sjasone cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 8581645Sjasone 8681645Sjasone mtx_unlock(&sema->sema_mtx); 8781645Sjasone} 8881645Sjasone 8981645Sjasonevoid 9081645Sjasone_sema_wait(struct sema *sema, const char *file, int line) 9181645Sjasone{ 9281645Sjasone 9381645Sjasone mtx_lock(&sema->sema_mtx); 9481645Sjasone while (sema->sema_value == 0) { 9581645Sjasone sema->sema_waiters++; 9681645Sjasone cv_wait(&sema->sema_cv, &sema->sema_mtx); 9781645Sjasone sema->sema_waiters--; 9881645Sjasone } 9981645Sjasone sema->sema_value--; 10081645Sjasone 10181645Sjasone CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema, 10281645Sjasone cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 10381645Sjasone 10481645Sjasone mtx_unlock(&sema->sema_mtx); 10581645Sjasone} 10681645Sjasone 10781645Sjasoneint 10881645Sjasone_sema_timedwait(struct sema *sema, int timo, const char *file, int line) 10981645Sjasone{ 11081645Sjasone int ret, timed_out; 11181645Sjasone 11281645Sjasone mtx_lock(&sema->sema_mtx); 11381645Sjasone 11481645Sjasone /* 11581645Sjasone * A spurious wakeup will cause the timeout interval to start over. 11681645Sjasone * This isn't a big deal as long as spurious wakeups don't occur 11781645Sjasone * continuously, since the timeout period is merely a lower bound on how 11881645Sjasone * long to wait. 11981645Sjasone */ 12081645Sjasone for (timed_out = 0; sema->sema_value == 0 && timed_out == 0;) { 12181645Sjasone sema->sema_waiters++; 12281645Sjasone timed_out = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo); 12381645Sjasone sema->sema_waiters--; 12481645Sjasone } 12581645Sjasone if (sema->sema_value > 0) { 12681645Sjasone /* Success. */ 12781645Sjasone sema->sema_value--; 12881645Sjasone ret = 1; 12981645Sjasone 13081645Sjasone CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema, 13181645Sjasone cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 13281645Sjasone } else { 13381645Sjasone ret = 0; 13481645Sjasone 13581645Sjasone CTR4(KTR_LOCK, __func__ "(%p) \"%s\" fail at %s:%d", sema, 13681645Sjasone cv_wmesg(&sema->sema_cv), file, line); 13781645Sjasone } 13881645Sjasone 13981645Sjasone mtx_unlock(&sema->sema_mtx); 14081645Sjasone return (ret); 14181645Sjasone} 14281645Sjasone 14381645Sjasoneint 14481645Sjasone_sema_trywait(struct sema *sema, const char *file, int line) 14581645Sjasone{ 14681645Sjasone int ret; 14781645Sjasone 14881645Sjasone mtx_lock(&sema->sema_mtx); 14981645Sjasone 15081645Sjasone if (sema->sema_value > 0) { 15181645Sjasone /* Success. */ 15281645Sjasone sema->sema_value--; 15381645Sjasone ret = 1; 15481645Sjasone 15581645Sjasone CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema, 15681645Sjasone cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 15781645Sjasone } else { 15881645Sjasone ret = 0; 15981645Sjasone 16081645Sjasone CTR4(KTR_LOCK, __func__ "(%p) \"%s\" fail at %s:%d", sema, 16181645Sjasone cv_wmesg(&sema->sema_cv), file, line); 16281645Sjasone } 16381645Sjasone 16481645Sjasone mtx_unlock(&sema->sema_mtx); 16581645Sjasone return (ret); 16681645Sjasone} 16781645Sjasone 16881645Sjasoneint 16981645Sjasonesema_value(struct sema *sema) 17081645Sjasone{ 17181645Sjasone int ret; 17281645Sjasone 17381645Sjasone mtx_lock(&sema->sema_mtx); 17481645Sjasone ret = sema->sema_value; 17581645Sjasone mtx_unlock(&sema->sema_mtx); 17681645Sjasone return (ret); 17781645Sjasone} 178