1 /* semaphore.c
2 *
3 * Copyright 2012 Christopher Anderson <chris@nullcode.org>
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include <kernel/semaphore.h>
18
19 #include <kernel/thread.h>
20 #include <lk/debug.h>
21 #include <lk/err.h>
22
sem_init(semaphore_t * sem,int initial_count)23 void sem_init(semaphore_t *sem, int initial_count) {
24 *sem = (semaphore_t)SEMAPHORE_INITIAL_VALUE(*sem, initial_count);
25 }
26
sem_destroy(semaphore_t * sem)27 void sem_destroy(semaphore_t *sem) {
28 THREAD_LOCK(state);
29 sem->count = 0;
30 wait_queue_destroy(&sem->wait, true);
31 THREAD_UNLOCK(state);
32 }
33
sem_post(semaphore_t * sem,bool resched)34 int sem_post(semaphore_t *sem, bool resched) {
35 int ret = 0;
36
37 THREAD_LOCK(state);
38
39 /*
40 * If the count is or was negative then a thread is waiting for a resource, otherwise
41 * it's safe to just increase the count available with no downsides
42 */
43 if (unlikely(++sem->count <= 0))
44 ret = wait_queue_wake_one(&sem->wait, resched, NO_ERROR);
45
46 THREAD_UNLOCK(state);
47
48 return ret;
49 }
50
sem_wait(semaphore_t * sem)51 status_t sem_wait(semaphore_t *sem) {
52 status_t ret = NO_ERROR;
53 THREAD_LOCK(state);
54
55 /*
56 * If there are no resources available then we need to
57 * sit in the wait queue until sem_post adds some.
58 */
59 if (unlikely(--sem->count < 0))
60 ret = wait_queue_block(&sem->wait, INFINITE_TIME);
61
62 THREAD_UNLOCK(state);
63 return ret;
64 }
65
sem_trywait(semaphore_t * sem)66 status_t sem_trywait(semaphore_t *sem) {
67 status_t ret = NO_ERROR;
68 THREAD_LOCK(state);
69
70 if (unlikely(sem->count <= 0)) {
71 ret = ERR_NOT_READY;
72 } else {
73 sem->count--;
74 }
75
76 THREAD_UNLOCK(state);
77 return ret;
78 }
79
sem_timedwait(semaphore_t * sem,lk_time_t timeout)80 status_t sem_timedwait(semaphore_t *sem, lk_time_t timeout) {
81 status_t ret = NO_ERROR;
82 THREAD_LOCK(state);
83
84 if (unlikely(--sem->count < 0)) {
85 ret = wait_queue_block(&sem->wait, timeout);
86 if (ret < NO_ERROR) {
87 if (ret == ERR_TIMED_OUT) {
88 sem->count++;
89 }
90 }
91 }
92
93 THREAD_UNLOCK(state);
94 return ret;
95 }
96