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
|
/* Copyright (C) 2002-2013 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <errno.h>
#include <semaphore.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/wait.h>
int
main (void)
{
size_t ps = sysconf (_SC_PAGESIZE);
char tmpfname[] = "/tmp/tst-sem3.XXXXXX";
char data[ps];
void *mem;
int fd;
sem_t *s;
pid_t pid;
char *p;
fd = mkstemp (tmpfname);
if (fd == -1)
{
printf ("cannot open temporary file: %m\n");
exit (1);
}
/* Make sure it is always removed. */
unlink (tmpfname);
/* Create one page of data. */
memset (data, '\0', ps);
/* Write the data to the file. */
if (write (fd, data, ps) != (ssize_t) ps)
{
puts ("short write");
exit (1);
}
mem = mmap (NULL, ps, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (mem == MAP_FAILED)
{
printf ("mmap failed: %m\n");
exit (1);
}
s = (sem_t *) (((uintptr_t) mem + __alignof (sem_t))
& ~(__alignof (sem_t) - 1));
p = (char *) (s + 1);
if (sem_init (s, 1, 1) == -1)
{
puts ("init failed");
exit (1);
}
if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
{
puts ("1st wait failed");
exit (1);
}
errno = 0;
if (TEMP_FAILURE_RETRY (sem_trywait (s)) != -1)
{
puts ("trywait succeeded");
exit (1);
}
else if (errno != EAGAIN)
{
puts ("trywait didn't return EAGAIN");
exit (1);
}
*p = 0;
puts ("going to fork now");
pid = fork ();
if (pid == -1)
{
puts ("fork failed");
exit (1);
}
else if (pid == 0)
{
/* Play some lock ping-pong. It's our turn to unlock first. */
if ((*p)++ != 0)
{
puts ("child: *p != 0");
exit (1);
}
if (sem_post (s) == -1)
{
puts ("child: 1st post failed");
exit (1);
}
puts ("child done");
}
else
{
if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
{
printf ("parent: 2nd wait failed: %m\n");
exit (1);
}
if (*p != 1)
{
puts ("*p != 1");
exit (1);
}
puts ("parent done");
}
exit (0);
}
|
