2 * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the author nor the names of any co-contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
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
32 #ifndef _SYS_RWLOCK_H_
33 #define _SYS_RWLOCK_H_
35 #include <sys/_lock.h>
36 #include <sys/_rwlock.h>
39 #include <machine/atomic.h>
43 * The rw_lock field consists of several fields. The low bit indicates
44 * if the lock is locked with a read (shared) or write (exclusive) lock.
45 * A value of 0 indicates a write lock, and a value of 1 indicates a read
46 * lock. Bit 1 is a boolean indicating if there are any threads waiting
47 * for a read lock. Bit 2 is a boolean indicating if there are any threads
48 * waiting for a write lock. The rest of the variable's definition is
49 * dependent on the value of the first bit. For a write lock, it is a
50 * pointer to the thread holding the lock, similar to the mtx_lock field of
51 * mutexes. For read locks, it is a count of read locks that are held.
53 * When the lock is not locked by any thread, it is encoded as a read lock
56 * A note about memory barriers. Write locks need to use the same memory
57 * barriers as mutexes: _acq when acquiring a write lock and _rel when
58 * releasing a write lock. Read locks also need to use an _acq barrier when
59 * acquiring a read lock. However, since read locks do not update any
60 * locked data (modulo bugs of course), no memory barrier is needed to when
61 * releasing a read lock.
64 #define RW_LOCK_READ 0x01
65 #define RW_LOCK_READ_WAITERS 0x02
66 #define RW_LOCK_WRITE_WAITERS 0x04
67 #define RW_LOCK_FLAGMASK \
68 (RW_LOCK_READ | RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)
70 #define RW_OWNER(x) ((x) & ~RW_LOCK_FLAGMASK)
71 #define RW_READERS_SHIFT 3
72 #define RW_READERS(x) (RW_OWNER((x)) >> RW_READERS_SHIFT)
73 #define RW_READERS_LOCK(x) ((x) << RW_READERS_SHIFT | RW_LOCK_READ)
74 #define RW_ONE_READER (1 << RW_READERS_SHIFT)
76 #define RW_UNLOCKED RW_READERS_LOCK(0)
80 /* Very simple operations on rw_lock. */
82 /* Try to obtain a write lock once. */
83 #define _rw_write_lock(rw, tid) \
84 atomic_cmpset_acq_ptr(&(rw)->rw_lock, RW_UNLOCKED, (tid))
86 /* Release a write lock quickly if there are no waiters. */
87 #define _rw_write_unlock(rw, tid) \
88 atomic_cmpset_rel_ptr(&(rw)->rw_lock, (tid), RW_UNLOCKED)
91 * Full lock operations that are suitable to be inlined in non-debug
92 * kernels. If the lock cannot be acquired or released trivially then
93 * the work is deferred to another function.
96 /* Acquire a write lock. */
97 #define __rw_wlock(rw, tid, file, line) do { \
98 uintptr_t _tid = (uintptr_t)(tid); \
100 if (!_rw_write_lock((rw), _tid)) \
101 _rw_wlock_hard((rw), _tid, (file), (line)); \
104 /* Release a write lock. */
105 #define __rw_wunlock(rw, tid, file, line) do { \
106 uintptr_t _tid = (uintptr_t)(tid); \
108 if (!_rw_write_unlock((rw), _tid)) \
109 _rw_wunlock_hard((rw), _tid, (file), (line)); \
113 * Function prototypes. Routines that start with _ are not part of the
114 * external API and should not be called directly. Wrapper macros should
118 void rw_init(struct rwlock *rw, const char *name);
119 void rw_destroy(struct rwlock *rw);
120 void rw_sysinit(void *arg);
121 void _rw_wlock(struct rwlock *rw, const char *file, int line);
122 void _rw_wunlock(struct rwlock *rw, const char *file, int line);
123 void _rw_rlock(struct rwlock *rw, const char *file, int line);
124 void _rw_runlock(struct rwlock *rw, const char *file, int line);
125 void _rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file,
127 void _rw_wunlock_hard(struct rwlock *rw, uintptr_t tid, const char *file,
129 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
130 void _rw_assert(struct rwlock *rw, int what, const char *file, int line);
134 * Public interface for lock operations.
136 * XXX: Missing try and upgrade/downgrade.
140 #error LOCK_DEBUG not defined, include <sys/lock.h> before <sys/rwlock.h>
142 #if LOCK_DEBUG > 0 || defined(RWLOCK_NOINLINE)
143 #define rw_wlock(rw) _rw_wlock((rw), LOCK_FILE, LOCK_LINE)
144 #define rw_wunlock(rw) _rw_wunlock((rw), LOCK_FILE, LOCK_LINE)
146 #define rw_wlock(rw) \
147 __rw_wlock((rw), curthread, LOCK_FILE, LOCK_LINE)
148 #define rw_wunlock(rw) \
149 __rw_wunlock((rw), curthread, LOCK_FILE, LOCK_LINE)
151 #define rw_rlock(rw) _rw_rlock((rw), LOCK_FILE, LOCK_LINE)
152 #define rw_runlock(rw) _rw_runlock((rw), LOCK_FILE, LOCK_LINE)
154 #define rw_initialized(rw) lock_initalized(&(rw)->rw_object)
157 struct rwlock *ra_rw;
161 #define RW_SYSINIT(name, rw, desc) \
162 static struct rw_args name##_args = { \
166 SYSINIT(name##_rw_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
167 rw_sysinit, &name##_args); \
168 SYSUNINIT(name##_mtx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
172 * The INVARIANTS-enabled rw_assert() functionality.
174 * The constants need to be defined for INVARIANT_SUPPORT infrastructure
175 * support as _rw_assert() itself uses them and the latter implies that
176 * _rw_assert() must build.
178 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
179 #define RA_LOCKED LA_LOCKED
180 #define RA_RLOCKED LA_SLOCKED
181 #define RA_WLOCKED LA_XLOCKED
182 #define RA_UNLOCKED LA_UNLOCKED
186 #define rw_assert(rw, what) _rw_assert((rw), (what), LOCK_FILE, LOCK_LINE)
188 #define rw_assert(rw, what)
192 #endif /* !_SYS_RWLOCK_H_ */