1 /*
2 * Copyright 2014 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_TFLOCK_TICKET_H
28 #define CK_TFLOCK_TICKET_H
29
30 /*
31 * This is an implementation of task-fair locks derived from the work
32 * described in:
33 * John M. Mellor-Crummey and Michael L. Scott. 1991.
34 * Scalable reader-writer synchronization for shared-memory
35 * multiprocessors. SIGPLAN Not. 26, 7 (April 1991), 106-113.
36 */
37
38 #include <ck_cc.h>
39 #include <ck_pr.h>
40
41 struct ck_tflock_ticket {
42 uint32_t request;
43 uint32_t completion;
44 };
45 typedef struct ck_tflock_ticket ck_tflock_ticket_t;
46
47 #define CK_TFLOCK_TICKET_INITIALIZER { 0, 0 }
48
49 #define CK_TFLOCK_TICKET_RC_INCR 0x10000U /* Read-side increment. */
50 #define CK_TFLOCK_TICKET_WC_INCR 0x1U /* Write-side increment. */
51 #define CK_TFLOCK_TICKET_W_MASK 0xffffU /* Write-side mask. */
52 #define CK_TFLOCK_TICKET_WC_TOPMSK 0x8000U /* Write clear mask for overflow. */
53 #define CK_TFLOCK_TICKET_RC_TOPMSK 0x80000000U /* Read clear mask for overflow. */
54
55 CK_CC_INLINE static uint32_t
ck_tflock_ticket_fca_32(uint32_t * target,uint32_t mask,uint32_t delta)56 ck_tflock_ticket_fca_32(uint32_t *target, uint32_t mask, uint32_t delta)
57 {
58 uint32_t snapshot = ck_pr_load_32(target);
59 uint32_t goal;
60
61 for (;;) {
62 goal = (snapshot & ~mask) + delta;
63 if (ck_pr_cas_32_value(target, snapshot, goal, &snapshot) == true)
64 break;
65
66 ck_pr_stall();
67 }
68
69 return snapshot;
70 }
71
72 CK_CC_INLINE static void
ck_tflock_ticket_init(struct ck_tflock_ticket * pf)73 ck_tflock_ticket_init(struct ck_tflock_ticket *pf)
74 {
75
76 pf->request = pf->completion = 0;
77 ck_pr_barrier();
78 return;
79 }
80
81 CK_CC_INLINE static void
ck_tflock_ticket_write_lock(struct ck_tflock_ticket * lock)82 ck_tflock_ticket_write_lock(struct ck_tflock_ticket *lock)
83 {
84 uint32_t previous;
85
86 previous = ck_tflock_ticket_fca_32(&lock->request, CK_TFLOCK_TICKET_WC_TOPMSK,
87 CK_TFLOCK_TICKET_WC_INCR);
88 ck_pr_fence_atomic_load();
89 while (ck_pr_load_32(&lock->completion) != previous)
90 ck_pr_stall();
91
92 ck_pr_fence_lock();
93 return;
94 }
95
96 CK_CC_INLINE static void
ck_tflock_ticket_write_unlock(struct ck_tflock_ticket * lock)97 ck_tflock_ticket_write_unlock(struct ck_tflock_ticket *lock)
98 {
99
100 ck_pr_fence_unlock();
101 ck_tflock_ticket_fca_32(&lock->completion, CK_TFLOCK_TICKET_WC_TOPMSK,
102 CK_TFLOCK_TICKET_WC_INCR);
103 return;
104 }
105
106 CK_CC_INLINE static void
ck_tflock_ticket_read_lock(struct ck_tflock_ticket * lock)107 ck_tflock_ticket_read_lock(struct ck_tflock_ticket *lock)
108 {
109 uint32_t previous;
110
111 previous = ck_tflock_ticket_fca_32(&lock->request,
112 CK_TFLOCK_TICKET_RC_TOPMSK, CK_TFLOCK_TICKET_RC_INCR) &
113 CK_TFLOCK_TICKET_W_MASK;
114
115 ck_pr_fence_atomic_load();
116
117 while ((ck_pr_load_32(&lock->completion) &
118 CK_TFLOCK_TICKET_W_MASK) != previous) {
119 ck_pr_stall();
120 }
121
122 ck_pr_fence_lock();
123 return;
124 }
125
126 CK_CC_INLINE static void
ck_tflock_ticket_read_unlock(struct ck_tflock_ticket * lock)127 ck_tflock_ticket_read_unlock(struct ck_tflock_ticket *lock)
128 {
129
130 ck_pr_fence_unlock();
131 ck_tflock_ticket_fca_32(&lock->completion, CK_TFLOCK_TICKET_RC_TOPMSK,
132 CK_TFLOCK_TICKET_RC_INCR);
133 return;
134 }
135
136 #endif /* CK_TFLOCK_TICKET_H */
137