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# dio_fcntl

(PHP 4 >= 4.2.0, PHP 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.

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)

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.

Exemplo 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); ?>`

> Nota: esta função não é implementada na plataforma Windows

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