PHP flock() Function

Example

Lock and release a file:

<?php
$file = fopen("test.txt","w+");

// exclusive lock
if (flock($file,LOCK_EX)) {
  fwrite($file,"Add some text to the file.");
fflush($file);
  // release lock
  flock($file,LOCK_UN);
} else {
  echo "Error locking file!";
}
fclose($file);
?>

Definition and Usage

The flock() function locks and releases a file.

Syntax

flock( file, lock, block)

Parameter Values

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 - A shared lock (reader). Allow other processes to access the file LOCK_EX - An exclusive lock (writer). Prevent other processes from accessing the file LOCK_UN - Release the lock LOCK_NB - Avoid blocking other processes while locking
block	Optional. Set to 1 to block other processes while locking

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 - A shared lock (reader). Allow other processes to access the file
LOCK_EX - An exclusive lock (writer). Prevent other processes from accessing the file
LOCK_UN - Release the lock
LOCK_NB - Avoid blocking other processes while locking

block

Optional. Set to 1 to block other processes while locking

Technical Details

Return Value:	TRUE on success, FALSE on failure
PHP Version:	4.0+
PHP Changelog:	PHP 5.5: Added support for the block parameter on Windows PHP 5.3: Removed automatic unlocking on fclose(). Unlocking must now be done manually

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