flock

Description

PHP supports a portable way of locking complete files in an advisory way (which means all accessing programs have to use the same way of locking or it will not work).

flock() operates on handle which must be an open file pointer. operation is one of the following values:

• To acquire a shared lock (reader), set operation to LOCK_SH (set to 1 prior to PHP 4.0.1).

• To acquire an exclusive lock (writer), set operation to LOCK_EX (set to 2 prior to PHP 4.0.1).

• To release a lock (shared or exclusive), set operation to LOCK_UN (set to 3 prior to PHP 4.0.1).

• If you don't want flock() to block while locking, add LOCK_NB (4 prior to PHP 4.0.1) to operation.

flock() allows you to perform a simple reader/writer model which can be used on virtually every platform (including most Unix derivatives and even Windows). The optional third argument is set to TRUE if the lock would block (EWOULDBLOCK errno condition). The lock is released also by fclose() (which is also called automatically when script finished).

Returns TRUE on success or FALSE on failure.

<?php

$fp = fopen("/tmp/lock.txt", "w+");

if (flock($fp, LOCK_EX)) { // do an exclusive lock
    fwrite($fp, "Write something here\n");
    flock($fp, LOCK_UN); // release the lock
} else {
    echo "Couldn't lock the file !";
}

fclose($fp);

?>