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