(PHP 4, PHP 5)
flock — Portable advisory file locking
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). 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.
An open file pointer.
operation is one of the following:
The optional third argument is set to TRUE if the lock would block (EWOULDBLOCK errno condition).
성공할 경우 TRUE를, 실패할 경우 FALSE를 반환합니다.
| 버전 | 설명 |
|---|---|
| 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 |
Example #1 flock() example
<?php
$fp = fopen("/tmp/lock.txt", "w");
if (flock($fp, LOCK_EX)) { // do an exclusive lock
ftruncate($fp, 0); // truncate file
fwrite($fp, "Write something here\n");
flock($fp, LOCK_UN); // release the lock
} else {
echo "Couldn't get the lock!";
}
fclose($fp);
?>
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()).
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).