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#include <sched.h> /* sched_yield() */
36
37#ifdef __linux__
38#include <sys/eventfd.h>
39#endif
40
41static void uv__async_send(uv_loop_t* loop);
42static int uv__async_start(uv_loop_t* loop);
43
44
45int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {
46 int err;
47
48 err = uv__async_start(loop);
49 if (err)
50 return err;
51
52 uv__handle_init(loop, (uv_handle_t*)handle, UV_ASYNC);
53 handle->async_cb = async_cb;
54 handle->pending = 0;
55
56 QUEUE_INSERT_TAIL(&loop->async_handles, &handle->queue);
57 uv__handle_start(handle);
58
59 return 0;
60}
61
62
63int uv_async_send(uv_async_t* handle) {
64 /* Do a cheap read first. */
65 if (ACCESS_ONCE(int, handle->pending) != 0)
66 return 0;
67
68 /* Tell the other thread we're busy with the handle. */
69 if (cmpxchgi(&handle->pending, 0, 1) != 0)
70 return 0;
71
72 /* Wake up the other thread's event loop. */
73 uv__async_send(handle->loop);
74
75 /* Tell the other thread we're done. */
76 if (cmpxchgi(&handle->pending, 1, 2) != 1)
77 abort();
78
79 return 0;
80}
81
82
83/* Only call this from the event loop thread. */
84static int uv__async_spin(uv_async_t* handle) {
85 int i;
86 int rc;
87
88 for (;;) {
89 /* 997 is not completely chosen at random. It's a prime number, acyclical
90 * by nature, and should therefore hopefully dampen sympathetic resonance.
91 */
92 for (i = 0; i < 997; i++) {
93 /* rc=0 -- handle is not pending.
94 * rc=1 -- handle is pending, other thread is still working with it.
95 * rc=2 -- handle is pending, other thread is done.
96 */
97 rc = cmpxchgi(&handle->pending, 2, 0);
98
99 if (rc != 1)
100 return rc;
101
102 /* Other thread is busy with this handle, spin until it's done. */
103 cpu_relax();
104 }
105
106 /* Yield the CPU. We may have preempted the other thread while it's
107 * inside the critical section and if it's running on the same CPU
108 * as us, we'll just burn CPU cycles until the end of our time slice.
109 */
110 sched_yield();
111 }
112}
113
114
115void uv__async_close(uv_async_t* handle) {
116 uv__async_spin(handle);
117 QUEUE_REMOVE(&handle->queue);
118 uv__handle_stop(handle);
119}
120
121
122static void uv__async_io(uv_loop_t* loop, uv__io_t* w, unsigned int events) {
123 char buf[1024];
124 ssize_t r;
125 QUEUE queue;
126 QUEUE* q;
127 uv_async_t* h;
128
129 assert(w == &loop->async_io_watcher);
130
131 for (;;) {
132 r = read(w->fd, buf, sizeof(buf));
133
134 if (r == sizeof(buf))
135 continue;
136
137 if (r != -1)
138 break;
139
140 if (errno == EAGAIN || errno == EWOULDBLOCK)
141 break;
142
143 if (errno == EINTR)
144 continue;
145
146 abort();
147 }
148
149 QUEUE_MOVE(&loop->async_handles, &queue);
150 while (!QUEUE_EMPTY(&queue)) {
151 q = QUEUE_HEAD(&queue);
152 h = QUEUE_DATA(q, uv_async_t, queue);
153
154 QUEUE_REMOVE(q);
155 QUEUE_INSERT_TAIL(&loop->async_handles, q);
156
157 if (0 == uv__async_spin(h))
158 continue; /* Not pending. */
159
160 if (h->async_cb == NULL)
161 continue;
162
163 h->async_cb(h);
164 }
165}
166
167
168static void uv__async_send(uv_loop_t* loop) {
169 const void* buf;
170 ssize_t len;
171 int fd;
172 int r;
173
174 buf = "";
175 len = 1;
176 fd = loop->async_wfd;
177
178#if defined(__linux__)
179 if (fd == -1) {
180 static const uint64_t val = 1;
181 buf = &val;
182 len = sizeof(val);
183 fd = loop->async_io_watcher.fd; /* eventfd */
184 }
185#endif
186
187 do
188 r = write(fd, buf, len);
189 while (r == -1 && errno == EINTR);
190
191 if (r == len)
192 return;
193
194 if (r == -1)
195 if (errno == EAGAIN || errno == EWOULDBLOCK)
196 return;
197
198 abort();
199}
200
201
202static int uv__async_start(uv_loop_t* loop) {
203 int pipefd[2];
204 int err;
205
206 if (loop->async_io_watcher.fd != -1)
207 return 0;
208
209#ifdef __linux__
210 err = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
211 if (err < 0)
212 return UV__ERR(errno);
213
214 pipefd[0] = err;
215 pipefd[1] = -1;
216#else
217 err = uv__make_pipe(pipefd, UV_NONBLOCK_PIPE);
218 if (err < 0)
219 return err;
220#endif
221
222 uv__io_init(&loop->async_io_watcher, uv__async_io, pipefd[0]);
223 uv__io_start(loop, &loop->async_io_watcher, POLLIN);
224 loop->async_wfd = pipefd[1];
225
226 return 0;
227}
228
229
230int uv__async_fork(uv_loop_t* loop) {
231 if (loop->async_io_watcher.fd == -1) /* never started */
232 return 0;
233
234 uv__async_stop(loop);
235
236 return uv__async_start(loop);
237}
238
239
240void uv__async_stop(uv_loop_t* loop) {
241 if (loop->async_io_watcher.fd == -1)
242 return;
243
244 if (loop->async_wfd != -1) {
245 if (loop->async_wfd != loop->async_io_watcher.fd)
246 uv__close(loop->async_wfd);
247 loop->async_wfd = -1;
248 }
249
250 uv__io_stop(loop, &loop->async_io_watcher, POLLIN);
251 uv__close(loop->async_io_watcher.fd);
252 loop->async_io_watcher.fd = -1;
253}
254