1 /* $NetBSD: rwlock.h,v 1.19 2023/09/07 20:05:41 ad Exp $ */ 2 3 /*- 4 * Copyright (c) 2002, 2006, 2007, 2008, 2019, 2020 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Jason R. Thorpe and Andrew Doran. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 #ifndef _SYS_RWLOCK_H_ 33 #define _SYS_RWLOCK_H_ 34 35 /* 36 * The rwlock provides exclusive access when held as a "writer", 37 * and shared access when held as a "reader". 38 * 39 * Architectures may optionally provide stubs for the following functions to 40 * implement the easy (unlocked, no waiters) cases. If these stubs are 41 * provided, __HAVE_RW_STUBS should be defined. 42 * 43 * rw_enter() 44 * rw_exit() 45 * rw_tryenter() 46 */ 47 48 #if !defined(_KERNEL) 49 #include <sys/types.h> 50 #include <sys/inttypes.h> 51 #endif 52 53 typedef enum krw_t { 54 RW_READER = 0, 55 RW_WRITER = 1 56 } krw_t; 57 58 typedef struct krwlock krwlock_t; 59 60 #ifdef __RWLOCK_PRIVATE 61 #include <sys/stdbool.h> 62 /* 63 * Bits in the owner field of the lock that indicate lock state. If the 64 * WRITE_LOCKED bit is clear, then the owner field is actually a count of 65 * the number of readers. The rw_owner field is laid out like so: 66 * 67 * N 5 4 3 2 1 0 68 * +------------------------------------------------------------------+ 69 * | owner or read count | nodbug | <free> | wrlock | wrwant | wait | 70 * +------------------------------------------------------------------+ 71 */ 72 #define RW_HAS_WAITERS 0x01UL /* lock has waiters */ 73 #define RW_WRITE_WANTED 0x02UL /* >= 1 waiter is a writer */ 74 #define RW_WRITE_LOCKED 0x04UL /* lock is currently write locked */ 75 #define RW_NODEBUG 0x10UL /* LOCKDEBUG disabled */ 76 77 #define RW_READ_COUNT_SHIFT 5 78 #define RW_READ_INCR (1UL << RW_READ_COUNT_SHIFT) 79 #define RW_THREAD ((uintptr_t)-RW_READ_INCR) 80 #define RW_OWNER(rw) ((rw)->rw_owner & RW_THREAD) 81 #define RW_COUNT(rw) ((rw)->rw_owner & RW_THREAD) 82 #define RW_FLAGS(rw) ((rw)->rw_owner & ~RW_THREAD) 83 84 void rw_vector_enter(krwlock_t *, const krw_t); 85 void rw_vector_exit(krwlock_t *); 86 int rw_vector_tryenter(krwlock_t *, const krw_t); 87 #endif /* __RWLOCK_PRIVATE */ 88 89 struct krwlock { 90 volatile uintptr_t rw_owner; 91 }; 92 93 #ifdef _KERNEL 94 95 void _rw_init(krwlock_t *, uintptr_t); 96 void rw_init(krwlock_t *); 97 void rw_destroy(krwlock_t *); 98 99 int rw_tryenter(krwlock_t *, const krw_t); 100 int rw_tryupgrade(krwlock_t *); 101 void rw_downgrade(krwlock_t *); 102 103 int rw_read_held(krwlock_t *); 104 int rw_write_held(krwlock_t *); 105 int rw_lock_held(krwlock_t *); 106 krw_t rw_lock_op(krwlock_t *); 107 108 void rw_enter(krwlock_t *, const krw_t); 109 void rw_exit(krwlock_t *); 110 111 void rw_obj_init(void); 112 krwlock_t *rw_obj_alloc(void); 113 void rw_obj_hold(krwlock_t *); 114 bool rw_obj_free(krwlock_t *); 115 u_int rw_obj_refcnt(krwlock_t *); 116 krwlock_t *rw_obj_tryalloc(void); 117 118 #endif /* _KERNEL */ 119 120 #endif /* _SYS_RWLOCK_H_ */ 121