1/* Copyright (C) 2012-2015 Free Software Foundation, Inc.
2   Contributed by Richard Henderson <rth@redhat.com>.
3
4   This file is part of the GNU Atomic Library (libatomic).
5
6   Libatomic is free software; you can redistribute it and/or modify it
7   under the terms of the GNU General Public License as published by
8   the Free Software Foundation; either version 3 of the License, or
9   (at your option) any later version.
10
11   Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
12   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
14   more details.
15
16   Under Section 7 of GPL version 3, you are granted additional
17   permissions described in the GCC Runtime Library Exception, version
18   3.1, as published by the Free Software Foundation.
19
20   You should have received a copy of the GNU General Public License and
21   a copy of the GCC Runtime Library Exception along with this program;
22   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23   <http://www.gnu.org/licenses/>.  */
24
25#include "libatomic_i.h"
26#include <pthread.h>
27
28
29/* The target page size.  Must be no larger than the runtime page size,
30   lest locking fail with virtual address aliasing (i.e. a page mmaped
31   at two locations).  */
32#ifndef PAGE_SIZE
33#define PAGE_SIZE	4096
34#endif
35
36/* The target cacheline size.  This is an optimization; the padding that
37   should be applied to the locks to keep them from interfering.  */
38#ifndef CACHLINE_SIZE
39#define CACHLINE_SIZE	64
40#endif
41
42/* The granularity at which locks are applied.  Almost certainly the
43   cachline size is the right thing to use here.  */
44#ifndef WATCH_SIZE
45#define WATCH_SIZE	CACHLINE_SIZE
46#endif
47
48struct lock
49{
50  pthread_mutex_t mutex;
51  char pad[sizeof(pthread_mutex_t) < CACHLINE_SIZE
52	   ? CACHLINE_SIZE - sizeof(pthread_mutex_t)
53	   : 0];
54};
55
56#define NLOCKS		(PAGE_SIZE / WATCH_SIZE)
57static struct lock locks[NLOCKS] = {
58  [0 ... NLOCKS-1].mutex = PTHREAD_MUTEX_INITIALIZER
59};
60
61static inline uintptr_t
62addr_hash (void *ptr)
63{
64  return ((uintptr_t)ptr / WATCH_SIZE) % NLOCKS;
65}
66
67void
68libat_lock_1 (void *ptr)
69{
70  pthread_mutex_lock (&locks[addr_hash (ptr)].mutex);
71}
72
73void
74libat_unlock_1 (void *ptr)
75{
76  pthread_mutex_unlock (&locks[addr_hash (ptr)].mutex);
77}
78
79void
80libat_lock_n (void *ptr, size_t n)
81{
82  uintptr_t h = addr_hash (ptr);
83  size_t i = 0;
84
85  /* Don't lock more than all the locks we have.  */
86  if (n > PAGE_SIZE)
87    n = PAGE_SIZE;
88
89  do
90    {
91      pthread_mutex_lock (&locks[h].mutex);
92      if (++h == NLOCKS)
93	h = 0;
94      i += WATCH_SIZE;
95    }
96  while (i < n);
97}
98
99void
100libat_unlock_n (void *ptr, size_t n)
101{
102  uintptr_t h = addr_hash (ptr);
103  size_t i = 0;
104
105  if (n > PAGE_SIZE)
106    n = PAGE_SIZE;
107
108  do
109    {
110      pthread_mutex_unlock (&locks[h].mutex);
111      if (++h == NLOCKS)
112	h = 0;
113      i += WATCH_SIZE;
114    }
115  while (i < n);
116}
117