Annotation of sys/sys/rwlock.h, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: rwlock.h,v 1.11 2007/05/29 00:17:32 thib Exp $ */
! 2: /*
! 3: * Copyright (c) 2002 Artur Grabowski <art@openbsd.org>
! 4: * All rights reserved.
! 5: *
! 6: * Redistribution and use in source and binary forms, with or without
! 7: * modification, are permitted provided that the following conditions
! 8: * are met:
! 9: *
! 10: * 1. Redistributions of source code must retain the above copyright
! 11: * notice, this list of conditions and the following disclaimer.
! 12: * 2. The name of the author may not be used to endorse or promote products
! 13: * derived from this software without specific prior written permission.
! 14: *
! 15: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
! 16: * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
! 17: * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
! 18: * THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
! 19: * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
! 20: * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
! 21: * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
! 22: * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
! 23: * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
! 24: * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
! 25: */
! 26:
! 27: /*
! 28: * Multiple readers, single writer lock.
! 29: *
! 30: * Simplistic implementation modelled after rw locks in Solaris.
! 31: *
! 32: * The rwl_owner has the following layout:
! 33: * [ owner or count of readers | wrlock | wrwant | wait ]
! 34: *
! 35: * When the WAIT bit is set (bit 0), the lock has waiters sleeping on it.
! 36: * When the WRWANT bit is set (bit 1), at least one waiter wants a write lock.
! 37: * When the WRLOCK bit is set (bit 2) the lock is currently write-locked.
! 38: *
! 39: * When write locked, the upper bits contain the struct proc * pointer to
! 40: * the writer, otherwise they count the number of readers.
! 41: *
! 42: * We provide a simple machine independent implementation that can be
! 43: * optimized by machine dependent code when __HAVE_MD_RWLOCK is defined.
! 44: *
! 45: * MD code that defines __HAVE_MD_RWLOCK and implement four functions:
! 46: *
! 47: * void rw_enter_read(struct rwlock *)
! 48: * atomically test for RWLOCK_WRLOCK and if not set, increment the lock
! 49: * by RWLOCK_READ_INCR. While RWLOCK_WRLOCK is set, loop into rw_enter_wait.
! 50: *
! 51: * void rw_enter_write(struct rwlock *);
! 52: * atomically test for the lock being 0 (it's not possible to have
! 53: * owner/read count unset and waiter bits set) and if 0 set the owner to
! 54: * the proc and RWLOCK_WRLOCK. While not zero, loop into rw_enter_wait.
! 55: *
! 56: * void rw_exit_read(struct rwlock *);
! 57: * atomically decrement lock by RWLOCK_READ_INCR and unset RWLOCK_WAIT and
! 58: * RWLOCK_WRWANT remembering the old value of lock and if RWLOCK_WAIT was set,
! 59: * call rw_exit_waiters with the old contents of the lock.
! 60: *
! 61: * void rw_exit_write(struct rwlock *);
! 62: * atomically swap the contents of the lock with 0 and if RWLOCK_WAIT was
! 63: * set, call rw_exit_waiters with the old contents of the lock.
! 64: *
! 65: * (XXX - the rest of the API for this is not invented yet).
! 66: */
! 67:
! 68: #ifndef SYS_RWLOCK_H
! 69: #define SYS_RWLOCK_H
! 70:
! 71:
! 72: struct proc;
! 73:
! 74: struct rwlock {
! 75: __volatile unsigned long rwl_owner;
! 76: const char *rwl_name;
! 77: };
! 78:
! 79: #define RWLOCK_INITIALIZER(name) { 0, name }
! 80:
! 81: #define RWLOCK_WAIT 0x01UL
! 82: #define RWLOCK_WRWANT 0x02UL
! 83: #define RWLOCK_WRLOCK 0x04UL
! 84: #define RWLOCK_MASK 0x07UL
! 85:
! 86: #define RWLOCK_OWNER(rwl) ((struct proc *)((rwl)->rwl_owner & ~RWLOCK_MASK))
! 87:
! 88: #define RWLOCK_READER_SHIFT 3UL
! 89: #define RWLOCK_READ_INCR (1UL << RWLOCK_READER_SHIFT)
! 90:
! 91: void rw_init(struct rwlock *, const char *);
! 92:
! 93: void rw_enter_read(struct rwlock *);
! 94: void rw_enter_write(struct rwlock *);
! 95: void rw_exit_read(struct rwlock *);
! 96: void rw_exit_write(struct rwlock *);
! 97:
! 98: int rw_enter(struct rwlock *, int);
! 99: void rw_exit(struct rwlock *);
! 100: #define RW_WRITE 0x00UL /* exclusive lock */
! 101: #define RW_READ 0x01UL /* shared lock */
! 102: #define RW_DOWNGRADE 0x02UL /* downgrade exclusive to shared */
! 103: #define RW_OPMASK 0x03UL
! 104:
! 105: #define RW_INTR 0x10UL /* interruptible sleep */
! 106: #define RW_SLEEPFAIL 0x20UL /* fail if we slept for the lock */
! 107: #define RW_NOSLEEP 0x40UL /* don't wait for the lock */
! 108:
! 109: #ifndef rw_cas
! 110: int rw_cas(volatile unsigned long *, unsigned long, unsigned long);
! 111: #endif
! 112:
! 113: #endif
CVSweb