使用PHP访问没有数据库的计数器

Question

I have a single webpage and i would like to track how many times it's visited without using a database.

I thought about XML, updating a file every time a user visits the page:

<?xml version='1.0' encoding='utf-8'?>
<counter>8</counter>

Then i thought it could have been a better idea to declare a PHP counter in a separate file and then update it everytime a user visits the page.

counter.php

<?php
    $counter = 0;
?>

update_counter.php:

<?php
    include "counter.php";
    $counter += 1;
    $var = "<?php
\t\$counter = $counter;
?>";
    file_put_contents('counter.php', $var);
?>

With this, everytime update_counter.php is visited, the variable in the counter.php file is incremented.

Anyway, i noticed that if the counter.php file has $counter = 5 and the update_counter.php file is visited by i.e. 1000 users at the exact same time, the file gets read 1000 times at the same time (so the the value 5 gets read in all requests) the counter.php file will be updated with value 5+1 (=6) instead of 1005.

Is there a way to make it work without using database?

Answer 1

You can use flock() which will lock the file so that other processes are not writing to the file.

Edit: updated to use fread() instead of include()

$fp = fopen("counter.txt", "r+");

while(!flock($fp, LOCK_EX)) {  // acquire an exclusive lock
    // waiting to lock the file
}

$counter = intval(fread($fp, filesize("counter.txt")));
$counter++;

ftruncate($fp, 0);      // truncate file
fwrite($fp, $counter);  // set your data
fflush($fp);            // flush output before releasing the lock
flock($fp, LOCK_UN);    // release the lock

fclose($fp);