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 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
23 * Copyright (c) 2014, 2015 by Delphix. All rights reserved.
24 */
25
26 /*
27 * A Zero Reference Lock (ZRL) is a reference count that can lock out new
28 * references only when the count is zero and only without waiting if the count
29 * is not already zero. It is similar to a read-write lock in that it allows
30 * multiple readers and only a single writer, but it does not allow a writer to
31 * block while waiting for readers to exit, and therefore the question of
32 * reader/writer priority is moot (no WRWANT bit). Since the equivalent of
33 * rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it
34 * is perfectly safe for the same reader to acquire the same lock multiple
35 * times. The fact that a ZRL is reentrant for readers (through multiple calls
36 * to zrl_add()) makes it convenient for determining whether something is
37 * actively referenced without the fuss of flagging lock ownership across
38 * function calls.
39 */
40 #include <sys/zrlock.h>
41
42 /*
43 * A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
54 cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL);
55 #ifdef ZFS_DEBUG
56 zrl->zr_owner = NULL;
57 zrl->zr_caller = NULL;
58 #endif
59 }
60
61 void
62 zrl_destroy(zrlock_t *zrl)
63 {
64 ASSERT0(zrl->zr_refcount);
65
66 mutex_destroy(&zrl->zr_mtx);
67 zrl->zr_refcount = ZRL_DESTROYED;
68 cv_destroy(&zrl->zr_cv);
69 }
70
71 void
72 zrl_add_impl(zrlock_t *zrl, const char *zc)
73 {
74 uint32_t n = (uint32_t)zrl->zr_refcount;
75
76 while (n != ZRL_LOCKED) {
77 uint32_t cas = atomic_cas_32(
78 (uint32_t *)&zrl->zr_refcount, n, n + 1);
79 if (cas == n) {
80 ASSERT3S((int32_t)n, >=, 0);
81 #ifdef ZFS_DEBUG
82 if (zrl->zr_owner == curthread) {
83 DTRACE_PROBE2(zrlock__reentry,
84 zrlock_t *, zrl, uint32_t, n);
85 }
86 zrl->zr_owner = curthread;
87 zrl->zr_caller = zc;
88 #endif
89 return;
90 }
91 n = cas;
92 }
93
94 mutex_enter(&zrl->zr_mtx);
95 while (zrl->zr_refcount == ZRL_LOCKED) {
96 cv_wait(&zrl->zr_cv, &zrl->zr_mtx);
97 }
98 ASSERT3S(zrl->zr_refcount, >=, 0);
99 zrl->zr_refcount++;
100 #ifdef ZFS_DEBUG
101 zrl->zr_owner = curthread;
102 zrl->zr_caller = zc;
103 #endif
104 mutex_exit(&zrl->zr_mtx);
105 }
106
107 void
108 zrl_remove(zrlock_t *zrl)
109 {
110 uint32_t n;
111
112 #ifdef ZFS_DEBUG
113 if (zrl->zr_owner == curthread) {
114 zrl->zr_owner = NULL;
115 zrl->zr_caller = NULL;
116 }
117 #endif
118 n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
119 ASSERT3S((int32_t)n, >=, 0);
120 }
121
122 int
123 zrl_tryenter(zrlock_t *zrl)
124 {
|
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 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
23 * Copyright (c) 2014, 2015 by Delphix. All rights reserved.
24 * Copyright 2016 Spectra Logic Corporation. All rights reserved.
25 * Copyright 2016 The MathWorks, Inc. All rights reserved.
26 */
27
28 /*
29 * A Zero Reference Lock (ZRL) is a reference count that can lock out new
30 * references only when the count is zero and only without waiting if the count
31 * is not already zero. It is similar to a read-write lock in that it allows
32 * multiple readers and only a single writer, but it does not allow a writer to
33 * block while waiting for readers to exit, and therefore the question of
34 * reader/writer priority is moot (no WRWANT bit). Since the equivalent of
35 * rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it
36 * is perfectly safe for the same reader to acquire the same lock multiple
37 * times. The fact that a ZRL is reentrant for readers (through multiple calls
38 * to zrl_add()) makes it convenient for determining whether something is
39 * actively referenced without the fuss of flagging lock ownership across
40 * function calls.
41 */
42 #include <sys/zrlock.h>
43
44 /*
45 * A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
56 cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL);
57 #ifdef ZFS_DEBUG
58 zrl->zr_owner = NULL;
59 zrl->zr_caller = NULL;
60 #endif
61 }
62
63 void
64 zrl_destroy(zrlock_t *zrl)
65 {
66 ASSERT0(zrl->zr_refcount);
67
68 mutex_destroy(&zrl->zr_mtx);
69 zrl->zr_refcount = ZRL_DESTROYED;
70 cv_destroy(&zrl->zr_cv);
71 }
72
73 void
74 zrl_add_impl(zrlock_t *zrl, const char *zc)
75 {
76 for (;;) {
77 uint32_t n = (uint32_t)zrl->zr_refcount;
78
79 while (n != ZRL_LOCKED) {
80 uint32_t cas = atomic_cas_32(
81 (uint32_t *)&zrl->zr_refcount, n, n + 1);
82
83 if (cas == n) {
84 ASSERT3S((int32_t)n, >=, 0);
85 #ifdef ZFS_DEBUG
86 if (zrl->zr_owner == curthread) {
87 DTRACE_PROBE2(zrlock__reentry,
88 zrlock_t *, zrl, uint32_t, n);
89 }
90 zrl->zr_owner = curthread;
91 zrl->zr_caller = zc;
92 #endif
93 return;
94 }
95 n = cas;
96 }
97
98 mutex_enter(&zrl->zr_mtx);
99 while (zrl->zr_refcount == ZRL_LOCKED) {
100 cv_wait(&zrl->zr_cv, &zrl->zr_mtx);
101 }
102 mutex_exit(&zrl->zr_mtx);
103 }
104 }
105
106 void
107 zrl_remove(zrlock_t *zrl)
108 {
109 uint32_t n;
110
111 #ifdef ZFS_DEBUG
112 if (zrl->zr_owner == curthread) {
113 zrl->zr_owner = NULL;
114 zrl->zr_caller = NULL;
115 }
116 #endif
117 n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
118 ASSERT3S((int32_t)n, >=, 0);
119 }
120
121 int
122 zrl_tryenter(zrlock_t *zrl)
123 {
|