1 | /* Open File Description Locks Usage Example |
2 | Copyright (C) 1991-2022 Free Software Foundation, Inc. |
3 | |
4 | This program is free software; you can redistribute it and/or |
5 | modify it under the terms of the GNU General Public License |
6 | as published by the Free Software Foundation; either version 2 |
7 | of the License, or (at your option) any later version. |
8 | |
9 | This program is distributed in the hope that it will be useful, |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
12 | GNU General Public License for more details. |
13 | |
14 | You should have received a copy of the GNU General Public License |
15 | along with this program; if not, see <https://www.gnu.org/licenses/>. |
16 | */ |
17 | |
18 | #define _GNU_SOURCE |
19 | #include <stdio.h> |
20 | #include <sys/types.h> |
21 | #include <sys/stat.h> |
22 | #include <unistd.h> |
23 | #include <fcntl.h> |
24 | #include <pthread.h> |
25 | |
26 | #define FILENAME "/tmp/foo" |
27 | #define NUM_THREADS 3 |
28 | #define ITERATIONS 5 |
29 | |
30 | void * |
31 | thread_start (void *arg) |
32 | { |
33 | int i, fd, len; |
34 | long tid = (long) arg; |
35 | char buf[256]; |
36 | struct flock lck = { |
37 | .l_whence = SEEK_SET, |
38 | .l_start = 0, |
39 | .l_len = 1, |
40 | }; |
41 | |
42 | fd = open (file: "/tmp/foo" , O_RDWR | O_CREAT, 0666); |
43 | |
44 | for (i = 0; i < ITERATIONS; i++) |
45 | { |
46 | lck.l_type = F_WRLCK; |
47 | fcntl (fd: fd, F_OFD_SETLKW, &lck); |
48 | |
49 | len = sprintf (buf, "%d: tid=%ld fd=%d\n" , i, tid, fd); |
50 | |
51 | lseek (fd: fd, offset: 0, SEEK_END); |
52 | write (fd, buf, len); |
53 | fsync (fd); |
54 | |
55 | lck.l_type = F_UNLCK; |
56 | fcntl (fd: fd, F_OFD_SETLK, &lck); |
57 | |
58 | /* sleep to ensure lock is yielded to another thread */ |
59 | usleep (useconds: 1); |
60 | } |
61 | pthread_exit (NULL); |
62 | } |
63 | |
64 | int |
65 | main (int argc, char **argv) |
66 | { |
67 | long i; |
68 | pthread_t threads[NUM_THREADS]; |
69 | |
70 | truncate (FILENAME, length: 0); |
71 | |
72 | for (i = 0; i < NUM_THREADS; i++) |
73 | pthread_create (newthread: &threads[i], NULL, start_routine: thread_start, arg: (void *) i); |
74 | |
75 | pthread_exit (NULL); |
76 | return 0; |
77 | } |
78 | |