# flock

(PHP 4, PHP 5)

flock — Portable advisory file locking

### Description

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).

### Parameters

`handle`

  An open file pointer.

`operation`

  `operation` is one of the following:

  - `LOCK_SH` to acquire a shared lock (reader).
  - `LOCK_EX` to acquire an exclusive lock (writer).
  - `LOCK_UN` to release a lock (shared or exclusive).
  - `LOCK_NB` if you don't want flock() to block while locking. (not supported on Windows)
`wouldblock`

  The optional third argument is set to `TRUE` if the lock would block (EWOULDBLOCK errno condition).

### Return Values

Returns `TRUE` on success or `FALSE` on failure.

### ChangeLog

Version | Description
--- | ---
4.0.1 | The LOCK_XXX constants were added. Prior to that you must use 1 for `LOCK_SH`, 2 for `LOCK_EX`, 3 for `LOCK_UN` and 4 for `LOCK_NB`

### Examples

Example#1 flock() example

`<?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);
?>`

### Notes

> Note: flock() locks mandatory under Windows.

> Note: Because flock() requires a file pointer, you may have to use a special lock file to protect access to a file that you intend to truncate by opening it in write mode (with a "w" or "w+" argument to fopen()).

Warning

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).