1 /***
2 This file is part of PulseAudio.
3
4 Copyright 2006 Lennart Poettering
5
6 PulseAudio is free software; you can redistribute it and/or modify
7 it under the terms of the GNU Lesser General Public License as
8 published by the Free Software Foundation; either version 2.1 of the
9 License, or (at your option) any later version.
10
11 PulseAudio is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
18 ***/
19
20 #ifdef HAVE_CONFIG_H
21 #include <config.h>
22 #endif
23
24 #include <unistd.h>
25 #include <errno.h>
26
27 #include <pulsecore/atomic.h>
28 #include <pulsecore/log.h>
29 #include <pulsecore/thread.h>
30 #include <pulsecore/macro.h>
31 #include <pulsecore/core-util.h>
32 #include <pulse/xmalloc.h>
33
34 #include "fdsem.h"
35
36 /* For debugging purposes we can define _Y to put and extra thread
37 * yield between each operation. */
38
39 /* #define PROFILE */
40
41 #ifdef PROFILE
42 #define _Y pa_thread_yield()
43 #else
44 #define _Y do { } while(0)
45 #endif
46
47 struct pa_shmasyncq {
48 pa_fdsem *read_fdsem, *write_fdsem;
49 pa_shmasyncq_data *data;
50 };
51
is_power_of_two(unsigned size)52 static int is_power_of_two(unsigned size) {
53 return !(size & (size - 1));
54 }
55
reduce(pa_shmasyncq *l, int value)56 static int reduce(pa_shmasyncq *l, int value) {
57 return value & (unsigned) (l->n_elements - 1);
58 }
59
get_cell(pa_shmasyncq *l, unsigned i)60 static pa_atomic_t* get_cell(pa_shmasyncq *l, unsigned i) {
61 pa_assert(i < l->data->n_elements);
62
63 return (pa_atomic_t*) ((uint8*t) l->data + PA_ALIGN(sizeof(pa_shmasyncq_data)) + i * (PA_ALIGN(sizeof(pa_atomic_t)) + PA_ALIGN(element_size)))
64 }
65
66 static void *get_cell_data(pa_atomic_t *a) {
67 return (uint8_t*) a + PA_ALIGN(sizeof(atomic_t));
68 }
69
pa_shmasyncq_new(unsigned n_elements, size_t element_size, void *data, int fd[2])70 pa_shmasyncq *pa_shmasyncq_new(unsigned n_elements, size_t element_size, void *data, int fd[2]) {
71 pa_shmasyncq *l;
72
73 pa_assert(n_elements > 0);
74 pa_assert(is_power_of_two(n_elements));
75 pa_assert(element_size > 0);
76 pa_assert(data);
77 pa_assert(fd);
78
79 l = pa_xnew(pa_shmasyncq, 1);
80
81 l->data = data;
82 memset(data, 0, PA_SHMASYNCQ_SIZE(n_elements, element_size));
83
84 l->data->n_elements = n_elements;
85 l->data->element_size = element_size;
86
87 if (!(l->read_fdsem = pa_fdsem_new_shm(&d->read_fdsem_data))) {
88 pa_xfree(l);
89 return NULL;
90 }
91 fd[0] = pa_fdsem_get(l->read_fdsem);
92
93 if (!(l->write_fdsem = pa_fdsem_new(&d->write_fdsem_data, &fd[1]))) {
94 pa_fdsem_free(l->read_fdsem);
95 pa_xfree(l);
96 return NULL;
97 }
98
99 return l;
100 }
101
pa_shmasyncq_free(pa_shmasyncq *l, pa_free_cb_t free_cb)102 void pa_shmasyncq_free(pa_shmasyncq *l, pa_free_cb_t free_cb) {
103 pa_assert(l);
104
105 if (free_cb) {
106 void *p;
107
108 while ((p = pa_shmasyncq_pop(l, 0)))
109 free_cb(p);
110 }
111
112 pa_fdsem_free(l->read_fdsem);
113 pa_fdsem_free(l->write_fdsem);
114 pa_xfree(l);
115 }
116
pa_shmasyncq_push(pa_shmasyncq*l, void *p, int wait)117 int pa_shmasyncq_push(pa_shmasyncq*l, void *p, int wait) {
118 int idx;
119 pa_atomic_ptr_t *cells;
120
121 pa_assert(l);
122 pa_assert(p);
123
124 cells = PA_SHMASYNCQ_CELLS(l);
125
126 _Y;
127 idx = reduce(l, l->write_idx);
128
129 if (!pa_atomic_ptr_cmpxchg(&cells[idx], NULL, p)) {
130
131 if (!wait)
132 return -1;
133
134 /* pa_log("sleeping on push"); */
135
136 do {
137 pa_fdsem_wait(l->read_fdsem);
138 } while (!pa_atomic_ptr_cmpxchg(&cells[idx], NULL, p));
139 }
140
141 _Y;
142 l->write_idx++;
143
144 pa_fdsem_post(l->write_fdsem);
145
146 return 0;
147 }
148
pa_shmasyncq_pop(pa_shmasyncq*l, int wait)149 void* pa_shmasyncq_pop(pa_shmasyncq*l, int wait) {
150 int idx;
151 void *ret;
152 pa_atomic_ptr_t *cells;
153
154 pa_assert(l);
155
156 cells = PA_SHMASYNCQ_CELLS(l);
157
158 _Y;
159 idx = reduce(l, l->read_idx);
160
161 if (!(ret = pa_atomic_ptr_load(&cells[idx]))) {
162
163 if (!wait)
164 return NULL;
165
166 /* pa_log("sleeping on pop"); */
167
168 do {
169 pa_fdsem_wait(l->write_fdsem);
170 } while (!(ret = pa_atomic_ptr_load(&cells[idx])));
171 }
172
173 pa_assert(ret);
174
175 /* Guaranteed to succeed if we only have a single reader */
176 pa_assert_se(pa_atomic_ptr_cmpxchg(&cells[idx], ret, NULL));
177
178 _Y;
179 l->read_idx++;
180
181 pa_fdsem_post(l->read_fdsem);
182
183 return ret;
184 }
185
pa_shmasyncq_get_fd(pa_shmasyncq *q)186 int pa_shmasyncq_get_fd(pa_shmasyncq *q) {
187 pa_assert(q);
188
189 return pa_fdsem_get(q->write_fdsem);
190 }
191
pa_shmasyncq_before_poll(pa_shmasyncq *l)192 int pa_shmasyncq_before_poll(pa_shmasyncq *l) {
193 int idx;
194 pa_atomic_ptr_t *cells;
195
196 pa_assert(l);
197
198 cells = PA_SHMASYNCQ_CELLS(l);
199
200 _Y;
201 idx = reduce(l, l->read_idx);
202
203 for (;;) {
204 if (pa_atomic_ptr_load(&cells[idx]))
205 return -1;
206
207 if (pa_fdsem_before_poll(l->write_fdsem) >= 0)
208 return 0;
209 }
210
211 return 0;
212 }
213
pa_shmasyncq_after_poll(pa_shmasyncq *l)214 void pa_shmasyncq_after_poll(pa_shmasyncq *l) {
215 pa_assert(l);
216
217 pa_fdsem_after_poll(l->write_fdsem);
218 }
219