PHP - Direct I/O dio_fcntl() Function

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The PHP Direct I/O dio_fcntl() function is used to execute the operation given by cmd on the file descriptor fd. Some commands need additional arguments (args) to be specified.

An arg is an associative array when cmd is set to F_SETLK or F_SETLLW with the following keys: "start" is the mix where a lock starts, "length" is the size of a locked area. zero means an end of a file, "wenth" is where it refers to l_start: maybe SEEK_SET, SEEK_END, and SEEK_CUR, and "type" is a type of lock: can be F_RDLCK (read lock), F_WRLCK (write lock), or F_UNLCK (unlock).

Syntax

Below is the syntax of the PHP Direct I/O dio_fcntl() function −

mixed dio_fcntl(resource $fd, int $cmd, mixed $arg = NULL)

Parameters

Below are the parameters of the dio_fcntl() function −

• $fd − It is the file descriptor returned by dio_open().

• $cmd − It is the command to execute (for example, F_GETFD, F_SETFD).

• $arg − It is an optional argument for the command.

The $cmd can be one of the following operations −

• F_SETLK − The lock is set or cleared. If a lock is held by someone else, dio_fcntl() function can return -1.
• F_GETLK − The dio_fcntl() function can return an associative array if anyone else prevents the lock. If there are no obstacles, the "type" key can be set by F_UNLCK.
• F_SETLKW − It similar to F_SETLK, but in the case when a lock is held by someone else, the dio_fcntl() function can wait until the lock is released.
• F_DUPFD − Finds the smallest numbered file descriptor greater than or equal to arg, and can return it.
• F_SETFL − Changes the file descriptor flags to the value given by args, which can be one of O_APPEND, O_NONBLOCK, or O_ASYNC. To use O_ASYNC, you have to use the PCNTL extension.
• F_GETFL − Get file status flags.

Return Value

The dio_fcntl() function returns different results based on the command ($cmd). Depending on the command, it can return an integer, a boolean, or another type.

PHP Version

First introduced in core PHP 4.2.0, the dio_fcntl() function continues to function easily in PHP 5.1.0.

Example 1

This example shows how to duplicate a file descriptor with PHP Direct I/O dio_fcntl() function and F_DUPFD command.

<?php
   // Mention file descriptor here
   $fd = dio_open('/PHP/PhpProjects/myfile.txt', O_RDWR);
   $new_fd = dio_fcntl($fd, F_DUPFD, 0);
   echo "New file descriptor: " . $new_fd;
   dio_close($fd);
?>

Output

The above code will result something like this −

New file descriptor: 3

Example 2

In the below PHP code we will try to use the dio_fcntl() function and set a file lock using F_SETLK.

<?php
   // Mention file descriptor here
   $fd = dio_open('/PHP/PhpProjects/myfile.txt', O_RDWR);
   $lock = ['type' => F_WRLCK, 'whence' => SEEK_SET, 'start' => 0, 'length' => 0];
   dio_fcntl($fd, F_SETLK, $lock);
   echo "File lock set.";
   dio_close($fd);
?> 

Output

After running the above program, it generates the following output −

File lock set.

Example 3

Now in the below code we will use the dio_fcntl() function with F_GETLK command to get the status of a file lock.

<?php
   // Mention file descriptor here
   $fd = dio_open('/PHP/PhpProjects/myfile.txt', O_RDWR);
   $lock = ['type' => F_WRLCK, 'whence' => SEEK_SET, 'start' => 0, 'length' => 0];
   $result = dio_fcntl($fd, F_GETLK, $lock);
   print_r($result);
   dio_close($fd);   
?> 

Output

This will create the below output −

Array
(
    [type] => 0
    [whence] => 0
    [start] => 0
    [length] => 0
    [pid] => 0
)

Example 4

In the following example, we are using the dio_fcntl() function to set file status flags with the help of F_SETFL command.

<?php
   // Mention file descriptor here
   $fd = dio_open('/PHP/PhpProjects/myfile.txt', O_RDWR);
   dio_fcntl($fd, F_SETFL, O_NONBLOCK);
   echo "File status flags set.";
   dio_close($fd);
?> 

Output

When the above program is executed, it will produce the below output −

File status flags set.