region_to_test.l_whence = SEEK_SET;
region_to_test.l_start = start_byte;
region_to_test.l_len = SIZE_TO_TRY;
region_to_test.l_pid = -1;
printf("Testing F_RDLCK on region from %d to %d\n", start_byte, start_byte + SIZE_TO_TRY);
6. Еще раз проверьте блокировку файла:
res = fcntl(file_desc, F_GETLK, ®ion_to_test);
if (res == -1) {
fprintf(stderr, "F_GETLK failed\n");
exit(EXIT_FAILURE);
}
if (region_to_test.l_pid != -1) {
printf("Lock would fail. F_GETLK returned:\n");
show_lock_info(®ion_to_test);
} else {
printf("F_RDLCK — Lock would succeed\n");
}
}
close(file_desc);
exit(EXIT_SUCCESS);
}
void show_lock_info(struct flock *to_show) {
printf("\tl_type %d, ", to_show->l_type);
printf("l_whence %d, ", to_show->l_whence);
printf("l_start %d, (int)to_show->l_start);
printf("l_len %d, ", (int)to_show->l_len);
printf("l_pid %d\n", to_show->l_pid);
}
Для проверки блокировки сначала запустите программу lock3, затем выполните программу lock4, чтобы протестировать заблокированный файл. Сделайте это, запустив программу lock3 в фоновом режиме с помощью следующей команды:
$ ./lock3 &
$ process 1534 locking file
На экране появится приглашение для ввода команд, поскольку lock3 выполняется в фоновом режиме. Далее сразу же запустите программу lock4 с помощью следующей команды:
$ ./lock4
Вы получите вывод, приведенный далее с некоторыми пропусками для краткости:
Testing F_WRLCK on region from 0 to 5
F_WRLCK — Lock would succeed
Testing F_RDLCK on region from 0 to 5
F_RDLCK - Lock would succeed
...
Testing F_WRLCK on region from 10 to 15
Lock would fail. F_GETLK returned:
l_type 0, l_whence 0, l_start 10, l_len 20, l_pid 1534
Testing F_RDLCK on region from 10 to 15
F_RDLCK — Lock would succeed
Testing F_WRLCK on region from 15 to 20
Lock would fail. F_GETLK returned:
l_type 0, l_whence 0, l_start 10, l_len 20, l_pid 1534
Testing F_RDLCK on region from 15 to 20
F_RDLCK — Lock would succeed
...
Testing F_WRLCK on region from 25 to 30
Lock would fail. F_GETLK returned:
l_type 0, l_whence 0, l_start 10, l_len 20, l_pid 1534
Testing F_RDLCK on region from 25 to 30
F_RDLCK — Lock would succeed
...
Testing F_WRLCK on region from 40 to 45
Lock would fail. F_GETLK returned:
l_type 1, l_whence 0, l_start 40, l_len 10, l_pid 1534
Testing F_RDLCK on region from 40 to 45
Lock would fail. F_GETLK returned:
l_type 1, l_whence 0, l_start 40, l_len 10, l_pid 1534
...
Testing F_RDLCK on region from 95 to 100
F_RDLCK - Lock would succeed
Как это работает
