import fcntl fcntl.flock(fd, operation)
(PHP 4, PHP 5)
flock — Portable advisory file locking
bool flock ( resource $handle , int $operation [, int &$wouldblock ] )
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 lock is released also by fclose() (which is also called automatically when script finished).
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).
Returns TRUE on success or FALSE on failure.
Example #1 flock() example
flock() will not work on NFS and many other networked file systems. Check your operating system documentation for more details.
On some operating systems flock() is implemented at the process level. When using a multithreaded server API like ISAPI you may not be able to rely on flock() to protect files against other PHP scripts running in parallel threads of the same server instance!
flock() is not supported on antiquated filesystems like FAT and its derivates and will therefore always return FALSE under this environments (this is especially true for Windows 98 users).