# dio_fcntl

(PHP 4 >= 4.2.0, PHP 5 <= 5.0.5)

dio_fcntl — Performs a c library fcntl on fd

### Description

mixed dio_fcntl ( resource `$fd` , int `$cmd` [, mixed `$args` ] )

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

> Note: This function is not implemented on Windows platforms.

### Parameters

`fd`

  The file descriptor returned by dio_open().

`cmd`

  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`

  `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)

### Return Values

Returns the result of the C call.

### Examples

Example#1 Setting and clearing a lock

`<?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 succesfully set/cleared";
}
dio_close($fd);
?>`