PHP flock file locking exclusive operation test_PHP tutorial

For file operations in PHP, we will mostly use file locking to avoid conflicts when multiple users operate at the same time. Below, the editor will test and analyze some examples of exclusive file locking operations.

flock – lightweight consultation file locking

flock() function prototype

bool flock ( int handle, int operation [, int &wouldblock] )

PHP supports a lightweight method of locking all files in an advisory manner (that is, all accessing programs must lock in the same way, otherwise it will not work)

operation can be one of the following values:

To obtain a shared lock (reading program), set operation to LOCK_SH (set to 1 in versions prior to PHP 4.0.1).
To obtain an exclusive lock (writing program), set operation to LOCK_EX (set to 2 in versions prior to PHP 4.0.1).
To release a lock (whether shared or exclusive), set operation to LOCK_UN (set to 3 in versions prior to PHP 4.0.1).
If you don't want flock() to block on lock, add LOCK_NB to the operation (set to 4 in versions prior to PHP 4.0.1).
flock() allows the implementation of a simple read/write model that can be used on any platform (including most Unix derivatives and even Windows). The optional third parameter is set to TRUE if the lock would block (in case of EWOULDBLOCK error code). Lock operations can also be released by fclose() (also called automatically when the code completes execution).

Returns TRUE if successful, FALSE if failed.

Note:
Under Windows flock() will be enforced. The handle of the flock() operation must be an open file pointer.
Since flock() requires a file pointer, you may have to use a special lock file to protect access to files intended to be opened in write mode (adding "w" or "w+" to the fopen() function).
flock() cannot be used with NFS and some other network file systems. flock() does not support older file systems such as FAT and its derivatives. Therefore, always return FALSE in this environment (especially for Windows). Check your operating system's documentation for details.
On some operating systems flock() is implemented at the process level. When using a multi-threaded server API (such as ISAPI), it may not be possible to rely on flock() to protect the file, because the file can be processed by PHP scripts running in other parallel threads in the same server instance.

Exclusive test:

The following two files are similar, the difference is that the things written are different. First run the a.php file and keep it open, then run the b.php file, and then check the written file content. You will find The content of the b.php file was not written successfully!

The code is as follows

Copy code

代码如下	复制代码
// a.php if ( ! ($f = @fopen("flock.log","ab"))) exit; flock($f, LOCK_EX); while(TRUE) { fwrite($f, "an"); } ?> // b.php if ( ! ($f = @fopen("flock.log","ab"))) exit; flock($f, LOCK_EX); while(TRUE) { fwrite($f, "bn"); } ?>

// a.php if ( ! ($f = @fopen("flock.log","ab"))) exit; flock($f, LOCK_EX);

while(TRUE)

{

fwrite($f, "an");

}

?>

代码如下	复制代码
$file = 'temp.txt';     $fp = fopen($file,'a');       for($i = 0;$i < 5;$i++) { fwrite($fp, "11111111n"); sleep(1); } fclose($fp);

<🎜> // b.php<🎜> if ( ! ($f = @fopen("flock.log","ab"))) exit;<🎜> flock($f, LOCK_EX);<🎜> while(TRUE)<🎜> {<🎜> fwrite($f, "bn");<🎜> }<🎜> ?>

For example, we have two files, as follows. flocka.php

The code is as follows	Copy code
$file = 'temp.txt'; $fp = fopen($file,'a'); for($i = 0;$i < 5;$i++) {             fwrite($fp, "11111111n");          sleep(1); } fclose($fp);

flockb.php

代码如下	复制代码
$file = 'temp.txt';     $fp = fopen($file,'a');       for($i = 0;$i < 5;$i++)     {         fwrite($fp, "22222222n");     }       fclose($fp);

Run flocka.php first, then flockb.php immediately.
Result:
11111111
22222222
22222222
22222222
22222222
22222222
11111111
11111111
11111111
11111111
Note that when no file lock is added, the two files will write to the txt file at the same time.
Let’s modify the code of the two php files.
flocka.php

The code is as follows

代码如下	复制代码
$file = 'temp.txt';     $fp = fopen($file,'a');       if(flock($fp,LOCK_EX))     {         for($i = 0;$i < 5;$i++)         {             fwrite($fp, "11111111n");             sleep(1);         }         flock($fp,LOCK_UN);     }     fclose($fp);

Copy code

$file = 'temp.txt'; $fp = fopen($file,'a');

代码如下	复制代码
$file = 'temp.txt';     $fp = fopen($file,'a');       if(flock($fp,LOCK_EX))     {         for($i = 0;$i < 5;$i++)         {             fwrite($fp, "22222222n");         }          flock($fp,LOCK_UN);     }       fclose($fp);

If(flock($fp,LOCK_EX))
{
for($i = 0;$i < 5;$i++)
           {
                   fwrite($fp, "11111111n");
               sleep(1);
}
flock($fp,LOCK_UN);
}
fclose($fp);

flockb.php

The code is as follows

Copy code

$file = 'temp.txt';

$fp = fopen($file,'a');

If(flock($fp,LOCK_EX)) { for($i = 0;$i < 5;$i++)            {                   fwrite($fp, "22222222n"); } flock($fp,LOCK_UN); } fclose($fp);

Similarly run flocka.php first, and then flockb.php immediately.

You will find that flockb.php is in a waiting state before flocka.php finishes running. Only when flocka.php finishes running, flockb.php will continue to execute.

Output result: 11111111 11111111 11111111 11111111 11111111 22222222 22222222 22222222 22222222 22222222 In addition, when executing flock, the file lock will be automatically released http://www.bkjia.com/PHPjc/632777.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/632777.htmlTechArticleFor file operations in PHP, we mostly use file locking to avoid conflicts when multiple users operate at the same time. Let's test some file locking exclusive operations with everyone...