1 /******************************************************************************
2 *
3 * Copyright (C) 2014 Google, Inc.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at:
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 ******************************************************************************/
18
19 #define LOG_TAG "osi_semaphore"
20
21 #include <assert.h>
22 #include <errno.h>
23 #include <fcntl.h>
24 #include <string.h>
25 #include <sys/eventfd.h>
26 #include <utils/Log.h>
27
28 #include "semaphore.h"
29
30 #if !defined(EFD_SEMAPHORE)
31 # define EFD_SEMAPHORE (1 << 0)
32 #endif
33
34 struct semaphore_t {
35 int fd;
36 };
37
semaphore_new(unsigned int value)38 semaphore_t *semaphore_new(unsigned int value) {
39 semaphore_t *ret = malloc(sizeof(semaphore_t));
40 if (ret) {
41 ret->fd = eventfd(value, EFD_SEMAPHORE);
42 if (ret->fd == -1) {
43 ALOGE("%s unable to allocate semaphore: %s", __func__, strerror(errno));
44 free(ret);
45 ret = NULL;
46 }
47 }
48 return ret;
49 }
50
semaphore_free(semaphore_t * semaphore)51 void semaphore_free(semaphore_t *semaphore) {
52 if (semaphore->fd != -1)
53 close(semaphore->fd);
54 free(semaphore);
55 }
56
semaphore_wait(semaphore_t * semaphore)57 void semaphore_wait(semaphore_t *semaphore) {
58 assert(semaphore != NULL);
59 assert(semaphore->fd != -1);
60
61 uint64_t value;
62 if (eventfd_read(semaphore->fd, &value) == -1)
63 ALOGE("%s unable to wait on semaphore: %s", __func__, strerror(errno));
64 }
65
semaphore_try_wait(semaphore_t * semaphore)66 bool semaphore_try_wait(semaphore_t *semaphore) {
67 assert(semaphore != NULL);
68 assert(semaphore->fd != -1);
69
70 int flags = fcntl(semaphore->fd, F_GETFL);
71 if (flags == -1) {
72 ALOGE("%s unable to get flags for semaphore fd: %s", __func__, strerror(errno));
73 return false;
74 }
75 if (fcntl(semaphore->fd, F_SETFL, flags | O_NONBLOCK) == -1) {
76 ALOGE("%s unable to set O_NONBLOCK for semaphore fd: %s", __func__, strerror(errno));
77 return false;
78 }
79
80 eventfd_t value;
81 if (eventfd_read(semaphore->fd, &value) == -1)
82 return false;
83
84 if (fcntl(semaphore->fd, F_SETFL, flags) == -1)
85 ALOGE("%s unable to resetore flags for semaphore fd: %s", __func__, strerror(errno));
86 return true;
87 }
88
semaphore_post(semaphore_t * semaphore)89 void semaphore_post(semaphore_t *semaphore) {
90 assert(semaphore != NULL);
91 assert(semaphore->fd != -1);
92
93 if (eventfd_write(semaphore->fd, 1ULL) == -1)
94 ALOGE("%s unable to post to semaphore: %s", __func__, strerror(errno));
95 }
96
semaphore_get_fd(const semaphore_t * semaphore)97 int semaphore_get_fd(const semaphore_t *semaphore) {
98 assert(semaphore != NULL);
99 assert(semaphore->fd != -1);
100 return semaphore->fd;
101 }
102