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      1 /*
      2  * CDDL HEADER START
      3  *
      4  * The contents of this file are subject to the terms of the
      5  * Common Development and Distribution License (the "License").
      6  * You may not use this file except in compliance with the License.
      7  *
      8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      9  * or http://www.opensolaris.org/os/licensing.
     10  * See the License for the specific language governing permissions
     11  * and limitations under the License.
     12  *
     13  * When distributing Covered Code, include this CDDL HEADER in each
     14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     15  * If applicable, add the following below this CDDL HEADER, with the
     16  * fields enclosed by brackets "[]" replaced with your own identifying
     17  * information: Portions Copyright [yyyy] [name of copyright owner]
     18  *
     19  * CDDL HEADER END
     20  */
     21 
     22 /*
     23  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
     24  * Use is subject to license terms.
     25  */
     26 
     27 #ifndef _SYS_CONDVAR_IMPL_H
     28 #define	_SYS_CONDVAR_IMPL_H
     29 
     30 /*
     31  * Implementation-private definitions for condition variables
     32  */
     33 
     34 #ifndef	_ASM
     35 #include <sys/types.h>
     36 #include <sys/thread.h>
     37 #endif	/* _ASM */
     38 
     39 #ifdef	__cplusplus
     40 extern "C" {
     41 #endif
     42 
     43 #ifndef	_ASM
     44 
     45 /*
     46  * Condtion variables.
     47  */
     48 
     49 typedef struct _condvar_impl {
     50 	ushort_t	cv_waiters;
     51 } condvar_impl_t;
     52 
     53 #define	CV_HAS_WAITERS(cvp)	(((condvar_impl_t *)(cvp))->cv_waiters != 0)
     54 
     55 #endif	/* _ASM */
     56 
     57 
     58 /*
     59  * The cvwaitlock_t structure and associated macros provide an implementation
     60  * of a locking mechanism that allows recursion on the reader lock without
     61  * danger of a pending write lock elsewhere being able to cause a deadlock.
     62  * The provision for supporting recursion is necessary for use with the
     63  * netinfo (neti) kernel module when processing network data.
     64  *
     65  * Support for recursion (giving precedence to readers and allowing them
     66  * to enter even when a write is blocked) can result in write starvation.
     67  * There is no priority inheritence for this locking interface.
     68  */
     69 typedef	struct	cvwaitlock_s	{
     70 	kmutex_t	cvw_lock;
     71 	kcondvar_t	cvw_waiter;
     72 	int		cvw_refcnt;
     73 } cvwaitlock_t;
     74 
     75 
     76 #define	CVW_INIT(_c)		{				\
     77 	mutex_init(&(_c)->cvw_lock, NULL, MUTEX_DRIVER, NULL);	\
     78 	cv_init(&(_c)->cvw_waiter, NULL, CV_DRIVER, NULL);	\
     79 	(_c)->cvw_refcnt = 0;					\
     80 }
     81 
     82 #define	CVW_ENTER_READ(_c)	{				\
     83 	mutex_enter(&(_c)->cvw_lock);				\
     84 	while ((_c)->cvw_refcnt < 0)				\
     85 		cv_wait(&((_c)->cvw_waiter), &(_c)->cvw_lock);	\
     86 	(_c)->cvw_refcnt++;					\
     87 	mutex_exit(&(_c)->cvw_lock);				\
     88 }
     89 
     90 #define	CVW_ENTER_WRITE(_c)	{				\
     91 	mutex_enter(&(_c)->cvw_lock);				\
     92 	while ((_c)->cvw_refcnt != 0)				\
     93 		cv_wait(&((_c)->cvw_waiter), &(_c)->cvw_lock);	\
     94 	(_c)->cvw_refcnt = -1;					\
     95 	mutex_exit(&(_c)->cvw_lock);				\
     96 }
     97 
     98 #define	CVW_EXIT_READ(_c)	{			\
     99 	mutex_enter(&(_c)->cvw_lock);			\
    100 	ASSERT((_c)->cvw_refcnt > 0);			\
    101 	if ((--((_c)->cvw_refcnt)) == 0)		\
    102 		cv_broadcast(&(_c)->cvw_waiter);	\
    103 	mutex_exit(&(_c)->cvw_lock);			\
    104 }
    105 
    106 #define	CVW_EXIT_WRITE(_c)	{			\
    107 	mutex_enter(&(_c)->cvw_lock);			\
    108 	ASSERT((_c)->cvw_refcnt == -1);			\
    109 	(_c)->cvw_refcnt = 0;				\
    110 	cv_broadcast(&(_c)->cvw_waiter);		\
    111 	mutex_exit(&(_c)->cvw_lock);			\
    112 }
    113 
    114 #define	CVW_WRITE_TO_READ(_c)	{			\
    115 	mutex_enter(&(_c)->cvw_lock);			\
    116 	ASSERT((_c)->cvw_refcnt == -1);			\
    117 	(_c)->cvw_refcnt = 1;				\
    118 	cv_broadcast(&(_c)->cvw_waiter);		\
    119 	mutex_exit(&(_c)->cvw_lock);			\
    120 }
    121 
    122 #define	CVW_DESTROY(_c)	{				\
    123 	mutex_destroy(&(_c)->cvw_lock);			\
    124 	cv_destroy(&(_c)->cvw_waiter);			\
    125 }
    126 
    127 #ifdef	__cplusplus
    128 }
    129 #endif
    130 
    131 #endif	/* _SYS_CONDVAR_IMPL_H */
    132