flock

(PHP 3>= 3.0.7, PHP 4 >= 4.0.0)

flock -- Portable advisory file locking

Description

bool flock (int fp, int operation, int [wouldblock])

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 fp which must be an open file pointer. operation is one of the following values:

flock() allows you to perform a simple reader/writer model which can be used on virtually every platform (including most Unices and even Windows). The optional 3rd argument is set to TRUE if the lock would block (EWOULDBLOCK errno condition)

flock() returns TRUE on success and FALSE on error (e.g. when a lock could not be acquired).

Warning

On most operation systems flock() is implemented at the process level. When using a multithreaded server API like ISAPI you cannot rely on flock() to protect files against other PHP scripts running in parallel threads of the same server instance!