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
38struct ck_spinlock_hclh {
39	unsigned int wait;
40	unsigned int splice;
41	int cluster_id;
42	struct ck_spinlock_hclh *previous;
43};
44typedef struct ck_spinlock_hclh ck_spinlock_hclh_t;
45
46CK_CC_INLINE static void
47ck_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
61CK_CC_INLINE static bool
62ck_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
73CK_CC_INLINE static void
74ck_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
122CK_CC_INLINE static void
123ck_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