File locking with PHP functions

I'd like to know (from someone who knows the internals more than I do) whether the following functions lock files and to what extent: fopen($filename, 'w'); Does this function lock the file from writes until fclose()? Does it lock from reads as well? fopen($filename, 'r+'); Does this function lock the file from writes until fclose()? Does it lock the file from reads as well? file($filename); Does this function lock the file from writes until finished? Does it lock the file from reads as well? All this is in the context of a Linux/Unix web server. Paul -- Paul M. Foster http://noferblatz.com http://quillandmouse.com