1/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
2 * Permission is hereby granted, free of charge, to any person obtaining a copy
3 * of this software and associated documentation files (the "Software"), to
4 * deal in the Software without restriction, including without limitation the
5 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
6 * sell copies of the Software, and to permit persons to whom the Software is
7 * furnished to do so, subject to the following conditions:
8 *
9 * The above copyright notice and this permission notice shall be included in
10 * all copies or substantial portions of the Software.
11 *
12 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
13 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
14 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
15 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
16 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
17 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
18 * IN THE SOFTWARE.
19 */
20
21/* This file contains both the uv__async internal infrastructure and the
22 * user-facing uv_async_t functions.
23 */
24
25#include "uv.h"
26#include "internal.h"
27#include "atomic-ops.h"
28
29#include <errno.h>
30#include <stdio.h> /* snprintf() */
31#include <assert.h>
32#include <stdlib.h>
33#include <string.h>
34#include <unistd.h>
35
36static void uv__async_send(uv_loop_t* loop);
37static int uv__async_start(uv_loop_t* loop);
38static int uv__async_eventfd(void);
39
40
41int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {
42 int err;
43
44 err = uv__async_start(loop);
45 if (err)
46 return err;
47
48 uv__handle_init(loop, (uv_handle_t*)handle, UV_ASYNC);
49 handle->async_cb = async_cb;
50 handle->pending = 0;
51
52 QUEUE_INSERT_TAIL(&loop->async_handles, &handle->queue);
53 uv__handle_start(handle);
54
55 return 0;
56}
57
58
59int uv_async_send(uv_async_t* handle) {
60 /* Do a cheap read first. */
61 if (ACCESS_ONCE(int, handle->pending) != 0)
62 return 0;
63
64 /* Tell the other thread we're busy with the handle. */
65 if (cmpxchgi(&handle->pending, 0, 1) != 0)
66 return 0;
67
68 /* Wake up the other thread's event loop. */
69 uv__async_send(handle->loop);
70
71 /* Tell the other thread we're done. */
72 if (cmpxchgi(&handle->pending, 1, 2) != 1)
73 abort();
74
75 return 0;
76}
77
78
79/* Only call this from the event loop thread. */
80static int uv__async_spin(uv_async_t* handle) {
81 int rc;
82
83 for (;;) {
84 /* rc=0 -- handle is not pending.
85 * rc=1 -- handle is pending, other thread is still working with it.
86 * rc=2 -- handle is pending, other thread is done.
87 */
88 rc = cmpxchgi(&handle->pending, 2, 0);
89
90 if (rc != 1)
91 return rc;
92
93 /* Other thread is busy with this handle, spin until it's done. */
94 cpu_relax();
95 }
96}
97
98
99void uv__async_close(uv_async_t* handle) {
100 uv__async_spin(handle);
101 QUEUE_REMOVE(&handle->queue);
102 uv__handle_stop(handle);
103}
104
105
106static void uv__async_io(uv_loop_t* loop, uv__io_t* w, unsigned int events) {
107 char buf[1024];
108 ssize_t r;
109 QUEUE queue;
110 QUEUE* q;
111 uv_async_t* h;
112
113 assert(w == &loop->async_io_watcher);
114
115 for (;;) {
116 r = read(w->fd, buf, sizeof(buf));
117
118 if (r == sizeof(buf))
119 continue;
120
121 if (r != -1)
122 break;
123
124 if (errno == EAGAIN || errno == EWOULDBLOCK)
125 break;
126
127 if (errno == EINTR)
128 continue;
129
130 abort();
131 }
132
133 QUEUE_MOVE(&loop->async_handles, &queue);
134 while (!QUEUE_EMPTY(&queue)) {
135 q = QUEUE_HEAD(&queue);
136 h = QUEUE_DATA(q, uv_async_t, queue);
137
138 QUEUE_REMOVE(q);
139 QUEUE_INSERT_TAIL(&loop->async_handles, q);
140
141 if (0 == uv__async_spin(h))
142 continue; /* Not pending. */
143
144 if (h->async_cb == NULL)
145 continue;
146
147 h->async_cb(h);
148 }
149}
150
151
152static void uv__async_send(uv_loop_t* loop) {
153 const void* buf;
154 ssize_t len;
155 int fd;
156 int r;
157
158 buf = "";
159 len = 1;
160 fd = loop->async_wfd;
161
162#if defined(__linux__)
163 if (fd == -1) {
164 static const uint64_t val = 1;
165 buf = &val;
166 len = sizeof(val);
167 fd = loop->async_io_watcher.fd; /* eventfd */
168 }
169#endif
170
171 do
172 r = write(fd, buf, len);
173 while (r == -1 && errno == EINTR);
174
175 if (r == len)
176 return;
177
178 if (r == -1)
179 if (errno == EAGAIN || errno == EWOULDBLOCK)
180 return;
181
182 abort();
183}
184
185
186static int uv__async_start(uv_loop_t* loop) {
187 int pipefd[2];
188 int err;
189
190 if (loop->async_io_watcher.fd != -1)
191 return 0;
192
193 err = uv__async_eventfd();
194 if (err >= 0) {
195 pipefd[0] = err;
196 pipefd[1] = -1;
197 }
198 else if (err == UV_ENOSYS) {
199 err = uv__make_pipe(pipefd, UV__F_NONBLOCK);
200#if defined(__linux__)
201 /* Save a file descriptor by opening one of the pipe descriptors as
202 * read/write through the procfs. That file descriptor can then
203 * function as both ends of the pipe.
204 */
205 if (err == 0) {
206 char buf[32];
207 int fd;
208
209 snprintf(buf, sizeof(buf), "/proc/self/fd/%d", pipefd[0]);
210 fd = uv__open_cloexec(buf, O_RDWR);
211 if (fd >= 0) {
212 uv__close(pipefd[0]);
213 uv__close(pipefd[1]);
214 pipefd[0] = fd;
215 pipefd[1] = fd;
216 }
217 }
218#endif
219 }
220
221 if (err < 0)
222 return err;
223
224 uv__io_init(&loop->async_io_watcher, uv__async_io, pipefd[0]);
225 uv__io_start(loop, &loop->async_io_watcher, POLLIN);
226 loop->async_wfd = pipefd[1];
227
228 return 0;
229}
230
231
232int uv__async_fork(uv_loop_t* loop) {
233 if (loop->async_io_watcher.fd == -1) /* never started */
234 return 0;
235
236 uv__async_stop(loop);
237
238 return uv__async_start(loop);
239}
240
241
242void uv__async_stop(uv_loop_t* loop) {
243 if (loop->async_io_watcher.fd == -1)
244 return;
245
246 if (loop->async_wfd != -1) {
247 if (loop->async_wfd != loop->async_io_watcher.fd)
248 uv__close(loop->async_wfd);
249 loop->async_wfd = -1;
250 }
251
252 uv__io_stop(loop, &loop->async_io_watcher, POLLIN);
253 uv__close(loop->async_io_watcher.fd);
254 loop->async_io_watcher.fd = -1;
255}
256
257
258static int uv__async_eventfd(void) {
259#if defined(__linux__)
260 static int no_eventfd2;
261 static int no_eventfd;
262 int fd;
263
264 if (no_eventfd2)
265 goto skip_eventfd2;
266
267 fd = uv__eventfd2(0, UV__EFD_CLOEXEC | UV__EFD_NONBLOCK);
268 if (fd != -1)
269 return fd;
270
271 if (errno != ENOSYS)
272 return UV__ERR(errno);
273
274 no_eventfd2 = 1;
275
276skip_eventfd2:
277
278 if (no_eventfd)
279 goto skip_eventfd;
280
281 fd = uv__eventfd(0);
282 if (fd != -1) {
283 uv__cloexec(fd, 1);
284 uv__nonblock(fd, 1);
285 return fd;
286 }
287
288 if (errno != ENOSYS)
289 return UV__ERR(errno);
290
291 no_eventfd = 1;
292
293skip_eventfd:
294
295#endif
296
297 return UV_ENOSYS;
298}
299