PHP flock() Function
 Complete PHP Filesystem Reference
Definition and Usage
The flock() function locks or releases a file.
This function returns TRUE on success or FALSE on failure.
Syntax
| Parameter |
Description |
| file |
Required. Specifies an open file to lock or release |
| lock |
Required. Specifies what kind of lock to use. Possible
values:
- LOCK_SH - Shared lock (reader). Allow other processes to access the
file
- LOCK_EX - Exclusive lock (writer). Prevent other
processes from accessing the file
- LOCK_UN - Release a shared or exclusive lock
- LOCK_NB - Avoids blocking other processes while locking
|
| block |
Optional. Set to 1 to block other processes while locking |
Tips and Notes
Note: These locks only apply to the current PHP process. Other
processes can modify or delete a PHP-locked file if permissions allow.
Note: flock() is mandatory under Windows.
Tip: The lock is released also by fclose(), which is called automatically when
script is finished.
Example
<?php
$file = fopen("test.txt","w+");
// exclusive lock
if (flock($file,LOCK_EX))
{
fwrite($file,"Write something");
// release lock
flock($file,LOCK_UN);
}
else
{
echo "Error locking file!";
}
fclose($file);
?>
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Complete PHP Filesystem Reference
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