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
41struct ck_tflock_ticket {
42	uint32_t request;
43	uint32_t completion;
44};
45typedef 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
55CK_CC_INLINE static uint32_t
56ck_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
72CK_CC_INLINE static void
73ck_tflock_ticket_init(struct ck_tflock_ticket *pf)
74{
75
76	pf->request = pf->completion = 0;
77	ck_pr_barrier();
78	return;
79}
80
81CK_CC_INLINE static void
82ck_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
96CK_CC_INLINE static void
97ck_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
106CK_CC_INLINE static void
107ck_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
126CK_CC_INLINE static void
127ck_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