Locking Files with flock( ) : flock « File Directory « PHP

Locking Files with flock( )

    $fp = fopen( $filename,"w"); // open it for WRITING ("w")
    if (flock($fp, LOCK_EX)) {
            // do your file writes here
            flock($fp, LOCK_UN); // unlock the file
    } else {
            // flock( ) returned false, no lock obtained
            print "Could not lock $filename!\n";

Related examples in the same category

1.If file lock is not available, flock( ) will return immediately with false rather than wait for a lock to become available.
2.Using advisory file locking
3.The file locking mechanism in PHP makes processes queue up for their locks by default