1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
/*! \file include/semaphore.h
\brief Interface: POSIX 1003.1b semaphores for task synchronization
\author Markus L. Noga <markus@noga.de>
*/
/*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License
* at http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and
* limitations under the License.
*
* The Original Code is legOS code, released October 17, 1999.
*
* The Initial Developer of the Original Code is Markus L. Noga.
* Portions created by Markus L. Noga are Copyright (C) 1999
* Markus L. Noga. All Rights Reserved.
*
* Contributor(s): Markus L. Noga <markus@noga.de>
* Henner Zeller <H.Zeller@acm.org> (sem_timedwait())
*/
#ifndef __semaphore_h__
#define __semaphore_h__
#ifdef __cplusplus
extern "C" {
#endif
#include <config.h>
#include <time.h> /* time_t */
#include <atomic.h>
#ifdef CONF_SEMAPHORES
///////////////////////////////////////////////////////////////////////
//
// Definitions
//
///////////////////////////////////////////////////////////////////////
typedef atomic_t sem_t; //!< the semaphore data-type
#define EAGAIN 0xffff //!< the error code
///////////////////////////////////////////////////////////////////////
//
// Functions
//
///////////////////////////////////////////////////////////////////////
//! Initialize a semaphore
/*! sem_init() initializes the semaphore object pointed to by
* {sem} by setting its internal count to {value}
* \param sem a pointer to the semaphore to be initialized
* \param value the initial value for count
* \param pshared (this argument is ignored)
* \return (always 0)
*/
extern inline int sem_init(sem_t * sem, int pshared, unsigned int value)
{
*sem = (sem_t) value;
return 0;
}
//! Wait for semaphore (blocking)
/*! sem_wait() suspends the calling task until the semaphore
* pointed to by {sem} has non-zero count. It then atomically
* decreases the semaphore count.
* \param sem a pointer to the semaphore on which to wait
* \return 0 if wait returned immediately, EAGAIN if task did have to
* wait for the semaphore.
*/
extern int sem_wait(sem_t * sem);
/**
* Wait for semaphore (blocking with timeout).
*
* sem_timedwait() suspends the calleing task until either the semaphore
* pointed to by {sem} has non-zero count or the given absolute timeout
* passed. Note the timeout is an ABSOLUTE time not relative (yes the standard
* is that stupid); so if you want a relative waiting time, call the
* function with <code>get_system_up_time() + relativeTime</code>.
*
* If the semaphore reached a non-zero count its value is then atomically
* decreased.
*
* @param sem a pointer to the semaphore on which to wait
* @param abs_timeout the absolute timeout of this operation. If the
* semaphore cannot be locked up to this time, this function returns.
* @return 0 if the semaphore could successfully be locked; -1 if the
* timeout has been reached.
* @note in IEEE 1003.1, the timeout is passed as a struct timeval not
* a time_t.
*/
extern int sem_timedwait(sem_t * sem,
const time_t abs_timeout);
//! Try a wait for semaphore (non-blocking)
/*! sem_trywait() is a non-blocking variant of sem_wait(). If the
* semaphore pointed to by {sem} has non-zero count, the count
* is atomically decreased and sem_trywait immediately
* returns 0. If the semaphore count is zero, sem_trywait
* immediately returns with error EAGAIN.
* \param sem a pointer to the semaphore on which to attempt a wait
* \return 0 if decremented the semaphore or EAGAIN if can't
*
* NOTE: this is IRQ handler safe.
*/
extern int sem_trywait(sem_t * sem);
//! Post a semaphore
/*! sem_post() atomically increases the count of the semaphore
* pointed to by {sem}. This function never blocks and can
* safely be used in asynchronous signal handlers.
* \param sem a pointer to the semaphore to be signaled
* \return (always returns 0)
*/
extern inline int sem_post(sem_t * sem)
{
atomic_inc(sem);
return 0;
}
//
//! Get the semaphore value
//
extern inline int sem_getvalue(sem_t * sem, int *sval)
{
*sval = *sem;
return 0;
}
//! We're done with the semaphore, destroy it
/*! sem_destroy() destroys a semaphore object, freeing the
* resources it might hold.
* \param sem a pointer to the semaphore to be destroyed
* \return (always returns 0)
*
* NOTE: No tasks should be waiting on
* the semaphore at the time sem_destroy is called.
*/
extern inline int sem_destroy(sem_t * sem)
{
return 0;
}
#endif // CONF_SEMAPHORES
#ifdef __cplusplus
}
#endif
#endif // __semaphore_h__
|
