The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/sys/rwlock.h

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    1 /*-
    2  * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    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.
   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  * $FreeBSD$
   30  */
   31 
   32 #ifndef _SYS_RWLOCK_H_
   33 #define _SYS_RWLOCK_H_
   34 
   35 #include <sys/_lock.h>
   36 #include <sys/_rwlock.h>
   37 #include <sys/lock_profile.h>
   38 
   39 #ifdef _KERNEL
   40 #include <sys/pcpu.h>
   41 #include <machine/atomic.h>
   42 #endif
   43 
   44 /*
   45  * The rw_lock field consists of several fields.  The low bit indicates
   46  * if the lock is locked with a read (shared) or write (exclusive) lock.
   47  * A value of 0 indicates a write lock, and a value of 1 indicates a read
   48  * lock.  Bit 1 is a boolean indicating if there are any threads waiting
   49  * for a read lock.  Bit 2 is a boolean indicating if there are any threads
   50  * waiting for a write lock.  The rest of the variable's definition is
   51  * dependent on the value of the first bit.  For a write lock, it is a
   52  * pointer to the thread holding the lock, similar to the mtx_lock field of
   53  * mutexes.  For read locks, it is a count of read locks that are held.
   54  *
   55  * When the lock is not locked by any thread, it is encoded as a read lock
   56  * with zero waiters.
   57  *
   58  * A note about memory barriers.  Write locks need to use the same memory
   59  * barriers as mutexes: _acq when acquiring a write lock and _rel when
   60  * releasing a write lock.  Read locks also need to use an _acq barrier when
   61  * acquiring a read lock.  However, since read locks do not update any
   62  * locked data (modulo bugs of course), no memory barrier is needed when
   63  * releasing a read lock.
   64  */
   65 
   66 #define RW_LOCK_READ            0x01
   67 #define RW_LOCK_READ_WAITERS    0x02
   68 #define RW_LOCK_WRITE_WAITERS   0x04
   69 #define RW_LOCK_RECURSED        0x08
   70 #define RW_LOCK_FLAGMASK                                                \
   71         (RW_LOCK_READ | RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS |  \
   72         RW_LOCK_RECURSED)
   73 
   74 #define RW_OWNER(x)             ((x) & ~RW_LOCK_FLAGMASK)
   75 #define RW_READERS_SHIFT        4
   76 #define RW_READERS(x)           (RW_OWNER((x)) >> RW_READERS_SHIFT)
   77 #define RW_READERS_LOCK(x)      ((x) << RW_READERS_SHIFT | RW_LOCK_READ)
   78 #define RW_ONE_READER           (1 << RW_READERS_SHIFT)
   79 
   80 #define RW_UNLOCKED             RW_READERS_LOCK(0)
   81 #define RW_DESTROYED            (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)
   82 
   83 #ifdef _KERNEL
   84 
   85 /* Very simple operations on rw_lock. */
   86 
   87 /* Try to obtain a write lock once. */
   88 #define _rw_write_lock(rw, tid)                                         \
   89         atomic_cmpset_acq_ptr(&(rw)->rw_lock, RW_UNLOCKED, (tid))
   90 
   91 /* Release a write lock quickly if there are no waiters. */
   92 #define _rw_write_unlock(rw, tid)                                       \
   93         atomic_cmpset_rel_ptr(&(rw)->rw_lock, (tid), RW_UNLOCKED)
   94 
   95 /*
   96  * Full lock operations that are suitable to be inlined in non-debug
   97  * kernels.  If the lock cannot be acquired or released trivially then
   98  * the work is deferred to another function.
   99  */
  100 
  101 /* Acquire a write lock. */
  102 #define __rw_wlock(rw, tid, file, line) do {                            \
  103         uintptr_t _tid = (uintptr_t)(tid);                              \
  104                                                                         \
  105         if (!_rw_write_lock((rw), _tid))                                \
  106                 _rw_wlock_hard((rw), _tid, (file), (line));             \
  107         else                                                            \
  108                 lock_profile_obtain_lock_success(&(rw)->lock_object, 0, \
  109                     0, (file), (line));                                 \
  110 } while (0)
  111 
  112 /* Release a write lock. */
  113 #define __rw_wunlock(rw, tid, file, line) do {                          \
  114         uintptr_t _tid = (uintptr_t)(tid);                              \
  115                                                                         \
  116         if (!_rw_write_unlock((rw), _tid))                              \
  117                 _rw_wunlock_hard((rw), _tid, (file), (line));           \
  118 } while (0)
  119 
  120 /*
  121  * Function prototypes.  Routines that start with _ are not part of the
  122  * external API and should not be called directly.  Wrapper macros should
  123  * be used instead.
  124  */
  125 
  126 #define rw_init(rw, name)       rw_init_flags((rw), (name), 0)
  127 void    rw_init_flags(struct rwlock *rw, const char *name, int opts);
  128 void    rw_destroy(struct rwlock *rw);
  129 void    rw_sysinit(void *arg);
  130 int     rw_wowned(struct rwlock *rw);
  131 void    _rw_wlock(struct rwlock *rw, const char *file, int line);
  132 int     _rw_try_wlock(struct rwlock *rw, const char *file, int line);
  133 void    _rw_wunlock(struct rwlock *rw, const char *file, int line);
  134 void    _rw_rlock(struct rwlock *rw, const char *file, int line);
  135 int     _rw_try_rlock(struct rwlock *rw, const char *file, int line);
  136 void    _rw_runlock(struct rwlock *rw, const char *file, int line);
  137 void    _rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file,
  138             int line);
  139 void    _rw_wunlock_hard(struct rwlock *rw, uintptr_t tid, const char *file,
  140             int line);
  141 int     _rw_try_upgrade(struct rwlock *rw, const char *file, int line);
  142 void    _rw_downgrade(struct rwlock *rw, const char *file, int line);
  143 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  144 void    _rw_assert(struct rwlock *rw, int what, const char *file, int line);
  145 #endif
  146 
  147 /*
  148  * Public interface for lock operations.
  149  */
  150 
  151 #ifndef LOCK_DEBUG
  152 #error LOCK_DEBUG not defined, include <sys/lock.h> before <sys/rwlock.h>
  153 #endif
  154 #if LOCK_DEBUG > 0 || defined(RWLOCK_NOINLINE)
  155 #define rw_wlock(rw)            _rw_wlock((rw), LOCK_FILE, LOCK_LINE)
  156 #define rw_wunlock(rw)          _rw_wunlock((rw), LOCK_FILE, LOCK_LINE)
  157 #else
  158 #define rw_wlock(rw)                                                    \
  159         __rw_wlock((rw), curthread, LOCK_FILE, LOCK_LINE)
  160 #define rw_wunlock(rw)                                                  \
  161         __rw_wunlock((rw), curthread, LOCK_FILE, LOCK_LINE)
  162 #endif
  163 #define rw_rlock(rw)            _rw_rlock((rw), LOCK_FILE, LOCK_LINE)
  164 #define rw_runlock(rw)          _rw_runlock((rw), LOCK_FILE, LOCK_LINE)
  165 #define rw_try_rlock(rw)        _rw_try_rlock((rw), LOCK_FILE, LOCK_LINE)
  166 #define rw_try_upgrade(rw)      _rw_try_upgrade((rw), LOCK_FILE, LOCK_LINE)
  167 #define rw_try_wlock(rw)        _rw_try_wlock((rw), LOCK_FILE, LOCK_LINE)
  168 #define rw_downgrade(rw)        _rw_downgrade((rw), LOCK_FILE, LOCK_LINE)
  169 #define rw_sleep(chan, rw, pri, wmesg, timo)                            \
  170         _sleep((chan), &(rw)->lock_object, (pri), (wmesg), (timo))
  171 
  172 #define rw_initialized(rw)      lock_initalized(&(rw)->lock_object)
  173 
  174 struct rw_args {
  175         struct rwlock   *ra_rw;
  176         const char      *ra_desc;
  177 };
  178 
  179 #define RW_SYSINIT(name, rw, desc)                                      \
  180         static struct rw_args name##_args = {                           \
  181                 (rw),                                                   \
  182                 (desc),                                                 \
  183         };                                                              \
  184         SYSINIT(name##_rw_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE,        \
  185             rw_sysinit, &name##_args);                                  \
  186         SYSUNINIT(name##_rw_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE,    \
  187             rw_destroy, (rw))
  188 
  189 /*
  190  * Options passed to rw_init_flags().
  191  */
  192 #define RW_DUPOK        0x01
  193 #define RW_NOPROFILE    0x02
  194 #define RW_NOWITNESS    0x04
  195 #define RW_QUIET        0x08
  196 #define RW_RECURSE      0x10
  197 
  198 /*
  199  * The INVARIANTS-enabled rw_assert() functionality.
  200  *
  201  * The constants need to be defined for INVARIANT_SUPPORT infrastructure
  202  * support as _rw_assert() itself uses them and the latter implies that
  203  * _rw_assert() must build.
  204  */
  205 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  206 #define RA_LOCKED               LA_LOCKED
  207 #define RA_RLOCKED              LA_SLOCKED
  208 #define RA_WLOCKED              LA_XLOCKED
  209 #define RA_UNLOCKED             LA_UNLOCKED
  210 #define RA_RECURSED             LA_RECURSED
  211 #define RA_NOTRECURSED          LA_NOTRECURSED
  212 #endif
  213 
  214 #ifdef INVARIANTS
  215 #define rw_assert(rw, what)     _rw_assert((rw), (what), LOCK_FILE, LOCK_LINE)
  216 #else
  217 #define rw_assert(rw, what)
  218 #endif
  219 
  220 #endif /* _KERNEL */
  221 #endif /* !_SYS_RWLOCK_H_ */

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