dio_fcntl

The dio_fcntl() function performs the operation specified by cmd on the file descriptor fd. Some commands require additional arguments args to be supplied.

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

• whence - 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)

Returns the result of the C call.

<?php

$fd = dio_open('/dev/ttyS0', O_RDWR);

if (dio_fcntl($fd, F_SETLK, Array("type"=>F_WRLCK)) == -1) {
   // the file descriptor appears locked
   echo "The lock can not be cleared. It is held by someone else.";
} else {
   echo "Lock successfully set/cleared";
}

dio_close($fd);
?>