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# dio_fcntl

(PHP 4 >= 4.2.0, PHP 5 <= 5.0.4)

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); ?>`

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