PHP Manual: 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.

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 below) 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
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)

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 successfully set/cleared";
}

dio_close($fd);
?>

Notes

Note: This function is not implemented on Windows platforms.