1 /*
2 * Copyright 2013-2015 Olivier Houchard
3 * Copyright 2010-2015 Samy Al Bahra.
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 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #ifndef CK_SPINLOCK_HCLH_H
29 #define CK_SPINLOCK_HCLH_H
30
31 #include <ck_cc.h>
32 #include <ck_pr.h>
33 #include <ck_stdbool.h>
34 #include <ck_stddef.h>
35
36 #ifndef CK_F_SPINLOCK_HCLH
37 #define CK_F_SPINLOCK_HCLH
38 struct ck_spinlock_hclh {
39 unsigned int wait;
40 unsigned int splice;
41 int cluster_id;
42 struct ck_spinlock_hclh *previous;
43 };
44 typedef struct ck_spinlock_hclh ck_spinlock_hclh_t;
45
46 CK_CC_INLINE static void
ck_spinlock_hclh_init(struct ck_spinlock_hclh ** lock,struct ck_spinlock_hclh * unowned,int cluster_id)47 ck_spinlock_hclh_init(struct ck_spinlock_hclh **lock,
48 struct ck_spinlock_hclh *unowned,
49 int cluster_id)
50 {
51
52 unowned->previous = NULL;
53 unowned->wait = false;
54 unowned->splice = false;
55 unowned->cluster_id = cluster_id;
56 *lock = unowned;
57 ck_pr_barrier();
58 return;
59 }
60
61 CK_CC_INLINE static bool
ck_spinlock_hclh_locked(struct ck_spinlock_hclh ** queue)62 ck_spinlock_hclh_locked(struct ck_spinlock_hclh **queue)
63 {
64 struct ck_spinlock_hclh *head;
65 bool r;
66
67 head = ck_pr_load_ptr(queue);
68 r = ck_pr_load_uint(&head->wait);
69 ck_pr_fence_acquire();
70 return r;
71 }
72
73 CK_CC_INLINE static void
ck_spinlock_hclh_lock(struct ck_spinlock_hclh ** glob_queue,struct ck_spinlock_hclh ** local_queue,struct ck_spinlock_hclh * thread)74 ck_spinlock_hclh_lock(struct ck_spinlock_hclh **glob_queue,
75 struct ck_spinlock_hclh **local_queue,
76 struct ck_spinlock_hclh *thread)
77 {
78 struct ck_spinlock_hclh *previous, *local_tail;
79
80 /* Indicate to the next thread on queue that they will have to block. */
81 thread->wait = true;
82 thread->splice = false;
83 thread->cluster_id = (*local_queue)->cluster_id;
84 /* Make sure previous->previous doesn't appear to be NULL */
85 thread->previous = *local_queue;
86
87 /* Serialize with respect to update of local queue. */
88 ck_pr_fence_store_atomic();
89
90 /* Mark current request as last request. Save reference to previous request. */
91 previous = ck_pr_fas_ptr(local_queue, thread);
92 thread->previous = previous;
93
94 /* Wait until previous thread from the local queue is done with lock. */
95 ck_pr_fence_load();
96 if (previous->previous != NULL) {
97 while (ck_pr_load_uint(&previous->wait) == true &&
98 ck_pr_load_int(&previous->cluster_id) == thread->cluster_id &&
99 ck_pr_load_uint(&previous->splice) == false)
100 ck_pr_stall();
101
102 /* We're head of the global queue, we're done */
103 if (ck_pr_load_int(&previous->cluster_id) == thread->cluster_id &&
104 ck_pr_load_uint(&previous->splice) == false)
105 return;
106 }
107
108 /* Now we need to splice the local queue into the global queue. */
109 local_tail = ck_pr_load_ptr(local_queue);
110 previous = ck_pr_fas_ptr(glob_queue, local_tail);
111
112 ck_pr_store_uint(&local_tail->splice, true);
113
114 /* Wait until previous thread from the global queue is done with lock. */
115 while (ck_pr_load_uint(&previous->wait) == true)
116 ck_pr_stall();
117
118 ck_pr_fence_lock();
119 return;
120 }
121
122 CK_CC_INLINE static void
ck_spinlock_hclh_unlock(struct ck_spinlock_hclh ** thread)123 ck_spinlock_hclh_unlock(struct ck_spinlock_hclh **thread)
124 {
125 struct ck_spinlock_hclh *previous;
126
127 /*
128 * If there are waiters, they are spinning on the current node wait
129 * flag. The flag is cleared so that the successor may complete an
130 * acquisition. If the caller is pre-empted then the predecessor field
131 * may be updated by a successor's lock operation. In order to avoid
132 * this, save a copy of the predecessor before setting the flag.
133 */
134 previous = thread[0]->previous;
135
136 /* We have to pay this cost anyways, use it as a compiler barrier too. */
137 ck_pr_fence_unlock();
138 ck_pr_store_uint(&(*thread)->wait, false);
139
140 /*
141 * Predecessor is guaranteed not to be spinning on previous request,
142 * so update caller to use previous structure. This allows successor
143 * all the time in the world to successfully read updated wait flag.
144 */
145 *thread = previous;
146 return;
147 }
148 #endif /* CK_F_SPINLOCK_HCLH */
149 #endif /* CK_SPINLOCK_HCLH_H */
150