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
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
|
/****************************************************************************
* sched/sem_open.c
*
* Copyright (C) 2007, 2008, 2012 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/types.h>
#include <stdbool.h>
#include <stdarg.h>
#include <limits.h>
#include <fcntl.h>
#include <string.h>
#include <semaphore.h>
#include <errno.h>
#include <nuttx/kmalloc.h>
#include "sem_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Type Declarations
****************************************************************************/
/****************************************************************************
* Global Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: sem_open
*
* Description:
* This function establishes a connection between named semaphores and a
* task. Following a call to sem_open() with the semaphore name, the task
* may reference the semaphore associated with name using the address
* returned by this call. The semaphore may be used in subsequent calls
* to sem_wait(), sem_trywait(), and sem_post(). The semaphore remains
* usable until the semaphore is closed by a successful call to sem_close().
*
* If a task makes multiple calls to sem_open() with the same name, then
* the same semaphore address is returned (provided there have been no
* calls to sem_unlink()).
*
* Parameters:
* name - Semaphore name
* oflag - Semaphore creation options. This may either or both of the
* following bit settings.
* oflag = 0: Connect to the semaphore only if it already exists.
* oflag = O_CREAT: Connect to the semaphore if it exists, otherwise
* create the semaphore.
* oflag = O_CREAT|O_EXCL: Create a new semaphore
* unless one of this name already exists.
* Optional parameters. When the O_CREAT flag is specified, two optional
* parameters are expected:
* 1. mode_t mode (ignored), and
* 2. unsigned int value. This initial value of the semaphore. Valid
* initial values of the semaphore must be less than or equal to
* SEM_VALUE_MAX.
*
* Return Value:
* A pointer to sem_t or -1 (ERROR) if unsuccessful.
*
* Assumptions:
*
****************************************************************************/
FAR sem_t *sem_open (FAR const char *name, int oflag, ...)
{
int namelen;
FAR nsem_t *psem;
FAR sem_t *sem = (FAR sem_t*)ERROR;
va_list arg; /* Points to each un-named argument */
mode_t mode; /* Creation mode parameter (ignored) */
unsigned int value; /* Semaphore value parameter */
/* Make sure that a non-NULL name is supplied */
if (name)
{
/* The POSIX specification requires that the "check for the
* existence of a semaphore and the creation of the semaphore
* if it does not exist shall be atomic with respect to other
* processes executing sem_open()..." A simple sched_lock()
* should be sufficient to meet this requirement.
*/
sched_lock();
namelen = strlen(name);
if (namelen > 0)
{
/* See if the semaphore already exists */
psem = sem_findnamed(name);
if (psem)
{
/* It does. Check if the caller wanted to created
* a new semahore with this name.
*/
if (!(oflag & O_CREAT) || !(oflag & O_EXCL))
{
/* Allow a new connection to the semaphore */
psem->nconnect++;
sem = &psem->sem;
}
}
/* It doesn't exist. Should we create one? */
else if ((oflag & O_CREAT) != 0)
{
/* Set up to get the optional arguments needed to create
* a message queue.
*/
va_start(arg, oflag);
mode = va_arg(arg, mode_t);
value = va_arg(arg, unsigned int);
/* Verify that a legal initial value was selected. */
if (value <= SEM_VALUE_MAX)
{
/* Allocate memory for the new semaphore */
psem = (FAR nsem_t*)kmalloc((sizeof(nsem_t) + namelen + 1));
if (psem)
{
/* Initialize the named semaphore */
sem = &psem->sem;
sem_init(sem, 0, value);
psem->nconnect = 1;
psem->unlinked = false;
psem->name = (FAR char*)psem + sizeof(nsem_t);
strcpy(psem->name, name);
/* Add the new semaphore to the list of named
* semaphores
*/
dq_addfirst((FAR dq_entry_t*)psem, &g_nsems);
}
/* Clean-up variable argument stuff */
va_end(arg);
}
}
}
sched_unlock();
}
return sem;
}
|
