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Filesystem Functions
PHP Manual

# 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).

On versions of PHP before 5.3.2, 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). By default, this function will block until the requested lock is acquired; this may be controlled (on non-Windows platforms) with the `LOCK_NB` option documented below.

### Parameters

`handle`

  A file system pointer resource that is typically created using fopen().

`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).

  It is also possible to add `LOCK_NB` as a bitmask to one of the above operations if you don't want flock() to block while locking. (not supported on Windows)

`wouldblock`

  The optional third argument is set to 1 if the lock would block (EWOULDBLOCK errno condition). (not supported on Windows)

### Return Values

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

### Changelog

Version | Description
--- | ---
5.3.2 | The automatic unlocking when the file's resource handle is closed was removed. Unlocking now always has to be done manually.
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
$fp = fopen("/tmp/lock.txt", "r+");
if (flock($fp, LOCK_EX)) { // acquire an exclusive lock
ftruncate($fp, 0); // truncate file
fwrite($fp, "Write something here\n");
fflush($fp); // flush output before releasing the lock
flock($fp, LOCK_UN); // release the lock
} else {
echo "Couldn't get the lock!";
}
fclose($fp);
?>`

Example #2 flock() using the `LOCK_NB` option

`<?php
$fp = fopen('/tmp/lock.txt', 'r+');
/* Activate the LOCK_NB option on an LOCK_EX operation */
if(!flock($fp, LOCK_EX | LOCK_NB)) {
echo 'Unable to obtain lock';
exit(-1);
}
/* ... */
fclose($fp);
?>`

### Notes

> Note:

> flock() uses mandatory locking instead of advisory locking on Windows. Mandatory locking is also supported on Linux and System V based operating systems via the usual mechanism supported by the fcntl() system call: that is, if the file in question has the setgid permission bit set and the group execution bit cleared. On Linux, the file system will also need to be mounted with the mand option for this to work.

> 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()).

> Note:

> May only be used on file pointers returned by fopen() for local files, or file pointers pointing to userspace streams that implement the streamWrapper::stream_lock() method.

Warning

Assigning another value to `handle` argument in subsequent code will release the lock.

Warning

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).

filetype
fnmatch
Filesystem Functions
PHP Manual