1 /*
2 * Copyright 2010-2015 Samy Al Bahra.
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 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 #ifndef CK_SPINLOCK_CLH_H
28 #define CK_SPINLOCK_CLH_H
29
30 #include <ck_cc.h>
31 #include <ck_limits.h>
32 #include <ck_pr.h>
33 #include <ck_stdbool.h>
34 #include <ck_stddef.h>
35
36 #ifndef CK_F_SPINLOCK_CLH
37 #define CK_F_SPINLOCK_CLH
38
39 struct ck_spinlock_clh {
40 unsigned int wait;
41 struct ck_spinlock_clh *previous;
42 };
43 typedef struct ck_spinlock_clh ck_spinlock_clh_t;
44
45 CK_CC_INLINE static void
ck_spinlock_clh_init(struct ck_spinlock_clh ** lock,struct ck_spinlock_clh * unowned)46 ck_spinlock_clh_init(struct ck_spinlock_clh **lock, struct ck_spinlock_clh *unowned)
47 {
48
49 unowned->previous = NULL;
50 unowned->wait = false;
51 *lock = unowned;
52 ck_pr_barrier();
53 return;
54 }
55
56 CK_CC_INLINE static bool
ck_spinlock_clh_locked(struct ck_spinlock_clh ** queue)57 ck_spinlock_clh_locked(struct ck_spinlock_clh **queue)
58 {
59 struct ck_spinlock_clh *head;
60 bool r;
61
62 head = ck_pr_load_ptr(queue);
63 r = ck_pr_load_uint(&head->wait);
64 ck_pr_fence_acquire();
65 return r;
66 }
67
68 CK_CC_INLINE static void
ck_spinlock_clh_lock(struct ck_spinlock_clh ** queue,struct ck_spinlock_clh * thread)69 ck_spinlock_clh_lock(struct ck_spinlock_clh **queue, struct ck_spinlock_clh *thread)
70 {
71 struct ck_spinlock_clh *previous;
72
73 /* Indicate to the next thread on queue that they will have to block. */
74 thread->wait = true;
75 ck_pr_fence_store_atomic();
76
77 /*
78 * Mark current request as last request. Save reference to previous
79 * request.
80 */
81 previous = ck_pr_fas_ptr(queue, thread);
82 thread->previous = previous;
83
84 /* Wait until previous thread is done with lock. */
85 ck_pr_fence_load();
86 while (ck_pr_load_uint(&previous->wait) == true)
87 ck_pr_stall();
88
89 ck_pr_fence_lock();
90 return;
91 }
92
93 CK_CC_INLINE static void
ck_spinlock_clh_unlock(struct ck_spinlock_clh ** thread)94 ck_spinlock_clh_unlock(struct ck_spinlock_clh **thread)
95 {
96 struct ck_spinlock_clh *previous;
97
98 /*
99 * If there are waiters, they are spinning on the current node wait
100 * flag. The flag is cleared so that the successor may complete an
101 * acquisition. If the caller is pre-empted then the predecessor field
102 * may be updated by a successor's lock operation. In order to avoid
103 * this, save a copy of the predecessor before setting the flag.
104 */
105 previous = thread[0]->previous;
106
107 /*
108 * We have to pay this cost anyways, use it as a compiler barrier too.
109 */
110 ck_pr_fence_unlock();
111 ck_pr_store_uint(&(*thread)->wait, false);
112
113 /*
114 * Predecessor is guaranteed not to be spinning on previous request,
115 * so update caller to use previous structure. This allows successor
116 * all the time in the world to successfully read updated wait flag.
117 */
118 *thread = previous;
119 return;
120 }
121 #endif /* CK_F_SPINLOCK_CLH */
122 #endif /* CK_SPINLOCK_CLH_H */
123