Torsten Curdt’s weblog

Java 1.4 introduced the native io layer into the JDK. One of the nice things you can do with it is to execute a native file lock that gets acknowledged by both “fcntl”- and “flock”-style locking. This is tremendously helpful if you need to share resources with native programs. So what is in C

  int fd = open("/path/to/file", O_RDWR);

  if (flock(fd,LOCK_EX) != 0 ) { ... }

  printf("locked file\\npress return");
  char c = getchar();

  if (flock(fd,LOCK_UN) != 0 ) { ... }

  printf("released file\\n");
  close(fd);

  int fd = open("/path/to/file", O_RDWR);

  struct flock lock;
  lock.l_type = F_WRLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start = 0;
  lock.l_len = 0;
  lock.l_pid = 0;

  if (fcntl(fd, F_SETLK, &lock) == -1) { ... }

  printf("locked file\\npress return");
  char c = getchar();

  lock.l_type = F_UNLCK;

  if (fcntl(fd, F_SETLK, &lock) == -1) { ... }

  printf("released file\\n");
  close(fd);

becomes this in java

File file = new File("/path/to/file");
FileChannel channel = new RandomAccessFile(file, "rw").getChannel();
FileLock lock = channel.lock();

System.out.println("locked file\\npress return");
System.in.read();

lock.release();
System.out.println("released file\\n");

6. August 2006 | c, java