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78 lines
1.8 KiB
C
78 lines
1.8 KiB
C
/* Open File Description Locks Usage Example
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Copyright (C) 1991-2020 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <https://www.gnu.org/licenses/>.
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <pthread.h>
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#define FILENAME "/tmp/foo"
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#define NUM_THREADS 3
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#define ITERATIONS 5
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void *
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thread_start (void *arg)
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{
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int i, fd, len;
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long tid = (long) arg;
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char buf[256];
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struct flock lck = {
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.l_whence = SEEK_SET,
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.l_start = 0,
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.l_len = 1,
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};
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fd = open ("/tmp/foo", O_RDWR | O_CREAT, 0666);
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for (i = 0; i < ITERATIONS; i++)
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{
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lck.l_type = F_WRLCK;
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fcntl (fd, F_OFD_SETLKW, &lck);
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len = sprintf (buf, "%d: tid=%ld fd=%d\n", i, tid, fd);
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lseek (fd, 0, SEEK_END);
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write (fd, buf, len);
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fsync (fd);
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lck.l_type = F_UNLCK;
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fcntl (fd, F_OFD_SETLK, &lck);
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/* sleep to ensure lock is yielded to another thread */
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usleep (1);
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}
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pthread_exit (NULL);
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}
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int
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main (int argc, char **argv)
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{
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long i;
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pthread_t threads[NUM_THREADS];
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truncate (FILENAME, 0);
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for (i = 0; i < NUM_THREADS; i++)
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pthread_create (&threads[i], NULL, thread_start, (void *) i);
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pthread_exit (NULL);
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return 0;
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}
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