# PHP flock() Function

Complete PHP Filesystem Reference

## Definition and Usage

The flock() function locks or releases a file.

This function returns TRUE on success or FALSE on failure.

## Syntax

flock(file,lock,block)

Parameter | Description
--- | ---
file | Required. Specifies an open file to lock or release

lock

Required. Specifies what kind of lock to use.

Possible values:

- LOCK_SH - Shared lock (reader). Allow other processes to access the file
- LOCK_EX - Exclusive lock (writer). Prevent other processes from accessing the file
- LOCK_UN - Release a shared or exclusive lock
- LOCK_NB - Avoids blocking other processes while locking

block | Optional. Set to 1 to block other processes while locking

## Tips and Notes

Note: These locks only apply to the current PHP process. Other processes can modify or delete a PHP-locked file if permissions allow.

Note: flock() is mandatory under Windows.

Tip: The lock is released also by fclose(), which is called automatically when script is finished.

## Example

<?php
$file = fopen("test.txt","w+");
// exclusive lock
if (flock($file,LOCK_EX))
{
fwrite($file,"Write something");
// release lock
flock($file,LOCK_UN);
}
else
{
echo "Error locking file!";
}
fclose($file);
?>

Complete PHP Filesystem Reference

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