PHP flock() Function
Definition and Usage
The flock() function locks or unlocks a file.
Returns true on success. Returns false on failure.
Syntax
flock(file,lock,block)
| Parameter | Description |
|---|---|
| file | Required. Specifies the opened file to be locked or unlocked. |
| lock | Required. Specifies which locking type to use. |
| block | Optional. If set to 1 or true, it will block other processes when locking. |
Description
The operation of file It must be a file pointer that has already been opened.
lock The parameter can be one of the following values:
- To obtain a shared lock (reading program), set lock to LOCK_SH (set to 1 in versions prior to PHP 4.0.1).
- To obtain an exclusive lock (writing program), set lock to LOCK_EX (set to 2 in versions prior to PHP 4.0.1).
- To release the lock (whether shared or exclusive), set lock to LOCK_UN (set to 3 in versions prior to PHP 4.0.1).
- If you do not want flock() to block during locking, set lock Add LOCK_NB (set to 4 in versions prior to PHP 4.0.1).
Tips and Comments
Tip:Can be used fclose() To release the locking operation, the code will also automatically call when the execution is completed.
Note:Since flock() requires a file pointer, it may be necessary to use a special locking file to protect access to the file intended to be opened in write mode (add "w" or "w+" in the fopen() function).
Example
<?php
$file = fopen("test.txt","w+");
// exclusive locking
if (flock($file,LOCK_EX))
{
fwrite($file,"Write something");
// release lock
flock($file,LOCK_UN);
}
else
{
echo "Error locking file!";
}
fclose($file);
?>
