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#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <pthread.h>
pthread_t th[5] = {0};
void
flock_init(struct flock *f, short int type, off_t start, off_t len)
{
f->l_type = type;
f->l_start = start;
f->l_len = len;
}
int
flock_range_in_steps(int fd, int is_set, short l_type, int start, int end,
int step)
{
int ret = 0;
int i = 0;
struct flock f = {
0,
};
for (i = start; i + step < end; i += step) {
flock_init(&f, l_type, i, step);
ret = fcntl(fd, (is_set) ? F_SETLKW : F_GETLK, &f);
if (ret) {
perror("fcntl");
goto out;
}
}
out:
return ret;
}
void *
random_locker(void *arg)
{
int fd = *(int *)arg;
int i = 0;
int is_set = 0;
/* use thread id to choose GETLK or SETLK operation*/
is_set = pthread_self() % 2;
(void)flock_range_in_steps(fd, is_set, F_WRLCK, 0, 400, 1);
return NULL;
}
int
main(int argc, char **argv)
{
int fd = -1;
int ret = 1;
int i = 0;
char *fname = NULL;
if (argc < 2)
goto out;
fname = argv[1];
fd = open(fname, O_RDWR);
if (fd == -1) {
perror("open");
goto out;
}
ret = flock_range_in_steps(fd, 1, F_WRLCK, 0, 2000, 2);
for (i = 0; i < 5; i++) {
pthread_create(&th[i], NULL, random_locker, (void *)&fd);
}
ret = flock_range_in_steps(fd, 1, F_WRLCK, 0, 2000, 2);
for (i = 0; i < 5; i++) {
pthread_join(th[i], NULL);
}
out:
if (fd != -1)
close(fd);
return ret;
}
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