PHP | SplFileObject flock() Function

Last Updated : 11 Jul, 2025
The SplFileObject flock() function is an inbuilt function of Standard PHP Library (SPL) in PHP which is used to apply portable lock on the file. Syntax: 
bool SplFileObject::flock( $opr, $isBlock )
Parameters: This function accept two parameters as mentioned above and described below: $opr: It is used to specify the operation to be apply from the following list:
  • LOCK_SH: Acquire a shared lock (reader).
  • LOCK_EX: Acquire an exclusive lock (writer).
  • LOCK_UN: Release a lock.
  • LOCK_NB: Not block while locking.
$isBlock: This parameter is set to True if the lock is block. Return values: This function returns True on on success or False on failure. Note: Make sure the used file in below program named as gfg.txt and should have read and write permissions. Below Programs illustrate the SplFileObject::flock() function in PHP: Program 1: php 
<?php

// Create Spl Object
$file = new SplFileObject("gfg.txt", "w");

// Add an Exclusive lock to gfg.txt
if ($file->flock(LOCK_SH)) { 
    $file->ftruncate(0);
    $file->fwrite("Write GFG inside the gfg.txt");
    
    // Release the lock  
    $file->flock(LOCK_UN);
    echo "Success Lock and Unlock Operation";
} 
else {
    echo "No Lock Available";
}
?>
Output: 
Success Lock and Unlock Operation.
Program 2: php 
<?php

// Create SplFile Object
$file = new SplFileObject("gfg.txt", "w");

// Add an Exclusive lock to gfg.txt
if ($file->flock(LOCK_EX)) { 
    $file->ftruncate(0);
    $file->fwrite("Write GFG inside the gfg.txt");
    
    // Release the lock  
    $file->flock(LOCK_UN);
    echo "Success Exclusive Lock and Unlock Operation";
} else {
    echo "No Lock Available";
}
?>
Output: 
Success Exclusive Lock and Unlock Operation
Reference: https://www.php.net/manual/en/splfileobject.flock.php
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