The file descriptor returned by dio_open().

Can be one of the following operations:

• F_SETLK - Lock is set or cleared. If the lock is held by someone else dio_fcntl() returns -1.

• F_SETLKW - like F_SETLK, but in case the lock is held by someone else, dio_fcntl() waits until the lock is released.

• F_GETLK - dio_fcntl() returns an associative array (as described above) if someone else prevents lock. If there is no obstruction key "type" will set to F_UNLCK.

• F_DUPFD - finds the lowest numbered available file descriptor greater than or equal to args and returns them.

• F_SETFL - Sets the file descriptors flags to the value specified by args, which can be O_APPEND, O_NONBLOCK or O_ASYNC. To use O_ASYNC you will need to use the PCNTL extension.

args is an associative array, when cmd is F_SETLK or F_SETLLW, with the following keys:

• "start" - offset where lock begins

• "length" - size of locked area. zero means to end of file

• "wenth" - Where l_start is relative to: can be SEEK_SET, SEEK_END and SEEK_CUR

• "type" - type of lock: can be F_RDLCK (read lock), F_WRLCK (write lock) or F_UNLCK (unlock)