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
| /* ipcsemaphore.c
To compile : gcc -o sem ipcsemaphore.c
To run : ./sem */
#define _XOPEN_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
union semun {
int val;
struct semid_ds *buf;
char *array;
};
void die(char *msg) {
perror(msg);
fflush(stdout);
fflush(stderr);
exit(1);
}
int main() {
int i,j;
int pid;
int semid; /* semid of semaphore set */
key_t key ; /* key to pass to semget() */
int semflg = IPC_CREAT | 0666; /* semflg to pass to semget() */
int nsems = 1; /* nsems to pass to semget() */
int nsops; /* number of operations to do */
struct sembuf *sops = (struct sembuf *) malloc(2*sizeof(struct sembuf));
/* ptr to operations to perform */
/* generate key */
/* if ((key = ftok("Semaphore", 'Q')) == -1)
die("ftok"); */
key=1234567890;
/* set up semaphore */
printf("\nsemget: Setting up semaphore: semget(%d, %d %o)\n", (int)key, nsems, semflg);
fflush(stdout);
fflush(stderr);
if ((semid = semget(key, nsems, semflg)) == -1)
die("semget: semget failed");
if ((pid = fork()) < 0)
die("fork");
if (pid == 0) {
/* child */
i = 0;
while (i < 3) { /* allow for 3 semaphore sets */
nsops = 2;
/* wait for semaphore to reach zero */
sops[0].sem_num = 0; /* We only use one track */
sops[0].sem_op = 0; /* wait for semaphore flag to become zero */
sops[0].sem_flg = SEM_UNDO; /* take off semaphore asynchronous */
sops[1].sem_num = 0;
sops[1].sem_op = 1; /* increment semaphore -- take control of track */
sops[1].sem_flg = SEM_UNDO | IPC_NOWAIT; /* take off semaphore */
/* Recap the call to be made. */
printf("\nsemop:Child Calling semop(%d, &sops, %d) with:", semid, nsops);
for (j = 0; j < nsops; j++)
{
printf("\n\tsops[%d].sem_num = %d, ", j, sops[j].sem_num);
printf("sem_op = %d, ", sops[j].sem_op);
printf("sem_flg = %#o\n", sops[j].sem_flg);
}
/* Make the semop() call and report the results. */
if ((j = semop(semid, sops, nsops)) == -1)
{
perror("semop: semop failed");
} else {
printf("\n\nChild Process Taking Control of Track: %d/3 times\n", i+1);
sleep(5); /* DO Nothing for 5 seconds */
nsops = 1;
/* wait for semaphore to reach zero */
sops[0].sem_num = 0;
sops[0].sem_op = -1; /* Give UP COntrol of track */
sops[0].sem_flg = SEM_UNDO | IPC_NOWAIT; /* take off semaphore, asynchronous */
if ((j = semop(semid, sops, nsops)) == -1) {
perror("semop: semop failed");
} else {
printf("Child Process Giving up Control of Track: %d/3 times\n", i+1);
}
sleep(5); /* halt process to allow parent to catch semaphore change first */
}
++i;
}
} else { /* parent */
i = 0;
while (i < 3) { /* allow for 3 semaphore sets */
nsops = 2;
/* wait for semaphore to reach zero */
sops[0].sem_num = 0;
sops[0].sem_op = 0; /* wait for semaphore flag to become zero */
sops[0].sem_flg = SEM_UNDO; /* take off semaphore asynchronous */
sops[1].sem_num = 0;
sops[1].sem_op = 1; /* increment semaphore -- take control of track */
sops[1].sem_flg = SEM_UNDO | IPC_NOWAIT; /* take off semaphore */
/* Recap the call to be made. */
printf("\nsemop:Parent Calling semop(%d, &sops, %d) with:", semid, nsops);
for (j = 0; j < nsops; j++) {
printf("\n\tsops[%d].sem_num = %d, ", j, sops[j].sem_num);
printf("sem_op = %d, ", sops[j].sem_op);
printf("sem_flg = %#o\n", sops[j].sem_flg);
}
/* Make the semop() call and report the results. */
if ((j = semop(semid, sops, nsops)) == -1) {
perror("semop: semop failed");
} else {
printf("Parent Process Taking Control of Track: %d/3 times\n", i+1);
sleep(5); /* Sleep for 5 seconds */
nsops = 1;
/* wait for semaphore to reach zero */
sops[0].sem_num = 0;
sops[0].sem_op = -1; /* Give UP Control of track */
sops[0].sem_flg = SEM_UNDO | IPC_NOWAIT; /* take off semaphore, asynchronous */
if ((j = semop(semid, sops, nsops)) == -1) {
perror("semop: semop failed");
} else {
printf("Parent Process Giving up Control of Track: %d/3 times\n", i+1);
}
sleep(5); /* halt process to allow child to catch semaphore change first */
}
++i;
}
}
return 0;
} |
