flock() function in PHP

The flock() function locks or releases a file. The function returns TRUE on success and FALSE on failure.

Syntax

flock(file_pointer, operation, block)

Parameters

• file_pointer − A file pointer for open file to lock or release.

• operation − Specifies the lock to use:

  • LOCK_SH - Shared lock (reader)
  • LOCK_EX - Exclusive lock (writer)
  • LOCK_UN - Release a shared or exclusive lock

• block − Set to 1 if the lock would block

Return

The flock() function returns.

• TRUE on success
• FALSE on failure

Example

<?php
   $file_pointer = fopen("new.txt","w+");
   // shared lock
   if (flock($file_pointer,LOCK_SH)) {
      fwrite($file_pointer,"Some content");
      flock($file_pointer,LOCK_UN);
   } else {
      echo "Locking of file shows an error!";
   }
   fclose($file_pointer);
?>

Output

TRUE