(PHP 5 >= 5.1.0, PHP 7)
SplFileObject::flock — Portable file locking
$operation
   [, int &$wouldblock
  ] )Locks or unlocks the file in the same portable way as flock().
operation
       operation is one of the following:
       
LOCK_SH to acquire a shared lock (reader).
         
        LOCK_EX to acquire an exclusive lock (writer).
         
        LOCK_UN to release a lock (shared or exclusive).
         
        LOCK_NB to not block while locking (not supported on Windows).
         
        wouldblock
       Set to TRUE if the lock would block (EWOULDBLOCK errno condition).
      
   Întoarce valoarea TRUE în cazul
succesului sau FALSE în cazul eșecului.
  
Example #1 SplFileObject::flock() example
<?php
$file = new SplFileObject("/tmp/lock.txt", "w");
if ($file->flock(LOCK_EX)) { // do an exclusive lock
    $file->ftruncate(0);     // truncate file
    $file->fwrite("Write something here\n");
    $file->flock(LOCK_UN);   // release the lock    
} else {
    echo "Couldn't get the lock!";
}
?>