summaryrefslogtreecommitdiff
path: root/source/kit/shared_mutex.h
blob: d202090193767b2baf33845810901a06cc8d77dd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
//  Shared mutex can be used in shared memory for interprocess
//  synchronization.
//

#ifndef KIT_SHARED_MUTEX_H
#define KIT_SHARED_MUTEX_H

#include "atomic.h"
#include "threads.h"

#include <assert.h>
#include <string.h>

#ifdef __cplusplus
extern "C" {
#endif

#if defined(__GNUC__) || defined(__clang__)
#  pragma GCC diagnostic push
#  pragma GCC diagnostic ignored "-Wunused-function"
#  pragma GCC diagnostic ignored "-Wunknown-pragmas"
#  pragma GCC            push_options
#  pragma GCC            optimize("O3")
#endif

enum {
  KIT_SHARED_MUTEX_READY = 1,
  KIT_SHARED_MUTEX_LOCKED,
  KIT_SHARED_MUTEX_WRITER
};

typedef union {
  struct {
    i8 _Atomic state;
    i32        readers;
  };
  struct {
    u8 _pad[16];
  };
} kit_shared_mutex_t;

static void kit_shared_mutex_init(kit_shared_mutex_t *m) {
  assert(m != NULL);
  memset(m, 0, sizeof *m);

  atomic_store_explicit(&m->state, KIT_SHARED_MUTEX_READY,
                        memory_order_relaxed);
}

static i8 kit_shared_try_lock(kit_shared_mutex_t *m) {
  assert(m != NULL);

  for (;;) {
    i8 prev_state = KIT_SHARED_MUTEX_READY;
    if (atomic_compare_exchange_strong_explicit(
            &m->state, &prev_state, KIT_SHARED_MUTEX_LOCKED,
            memory_order_seq_cst, memory_order_seq_cst))
      break;
    if (prev_state == KIT_SHARED_MUTEX_WRITER)
      return 0;
    //  FIXME
    //  Check performance
    thrd_yield();
  }

  assert(m->readers >= 0);
  ++m->readers;

  i8 prev_state = KIT_SHARED_MUTEX_LOCKED;
  if (!atomic_compare_exchange_strong_explicit(
          &m->state, &prev_state, KIT_SHARED_MUTEX_READY,
          memory_order_seq_cst, memory_order_seq_cst))
    assert(0);

  return 1;
}

static void kit_shared_lock(kit_shared_mutex_t *m) {
  assert(m != NULL);

  while (!kit_shared_try_lock(m))
    //  FIXME
    //  Check performance
    thrd_yield();
}

static void kit_shared_unlock(kit_shared_mutex_t *m) {
  assert(m != NULL);

  for (;;) {
    i8 prev_state = KIT_SHARED_MUTEX_READY;
    if (atomic_compare_exchange_strong_explicit(
            &m->state, &prev_state, KIT_SHARED_MUTEX_LOCKED,
            memory_order_seq_cst, memory_order_seq_cst))
      break;
    //  FIXME
    //  Check performance
    thrd_yield();
  }

  assert(m->readers > 0);
  m->readers--;

  i8 prev_state = KIT_SHARED_MUTEX_LOCKED;
  if (!atomic_compare_exchange_strong_explicit(
          &m->state, &prev_state, KIT_SHARED_MUTEX_READY,
          memory_order_seq_cst, memory_order_seq_cst))
    assert(0);
}

static i8 kit_unique_try_lock(kit_shared_mutex_t *m) {
  assert(m != NULL);

  i8 prev_state = KIT_SHARED_MUTEX_READY;
  if (!atomic_compare_exchange_strong_explicit(
          &m->state, &prev_state, KIT_SHARED_MUTEX_WRITER,
          memory_order_seq_cst, memory_order_seq_cst))
    return 0;

  i8 is_locked = (m->readers == 0);

  prev_state = KIT_SHARED_MUTEX_WRITER;
  if (!is_locked &&
      !atomic_compare_exchange_strong_explicit(
          &m->state, &prev_state, KIT_SHARED_MUTEX_READY,
          memory_order_seq_cst, memory_order_seq_cst))
    assert(0);

  return is_locked;
}

static void kit_unique_lock(kit_shared_mutex_t *m) {
  assert(m != NULL);

  while (!kit_unique_try_lock(m))
    //  FIXME
    //  Check performance
    thrd_yield();
}

static void kit_unique_unlock(kit_shared_mutex_t *m) {
  assert(m != NULL);

  i8 prev_state = KIT_SHARED_MUTEX_WRITER;
  if (!atomic_compare_exchange_strong_explicit(
          &m->state, &prev_state, KIT_SHARED_MUTEX_READY,
          memory_order_seq_cst, memory_order_seq_cst))
    assert(0);
}

#if defined(__GNUC__) || defined(__clang__)
#  pragma GCC            pop_options
#  pragma GCC diagnostic pop
#endif

#ifdef __cplusplus
}
#endif

#define shared_mutex_t kit_shared_mutex_t
#define shared_mutex_init kit_shared_mutex_init
#define shared_try_lock kit_shared_try_lock
#define shared_lock kit_shared_lock
#define shared_unlock kit_shared_unlock
#define unique_try_lock kit_unique_try_lock
#define unique_lock kit_unique_lock
#define unique_unlock kit_unique_unlock
#define shared_mutex_init kit_shared_mutex_init
#define shared_try_lock kit_shared_try_lock
#define shared_lock kit_shared_lock
#define shared_unlock kit_shared_unlock
#define unique_try_lock kit_unique_try_lock
#define unique_lock kit_unique_lock
#define unique_unlock kit_unique_unlock

#endif