Can I use fastcgi_finish_request() like register_shutdown_function? - fastcgi

Question

This simple method for caching dynamic content uses register_shutdown_function() to push the output buffer to a file on disk after exiting the script. However, I'm using PHP-FPM, with which this doesn't work; a 5-second sleep added to the function indeed causes a 5-second delay in executing the script from the browser. A commenter in the PHP docs notes that there's a special function for PHP-FPM users, namely fastcgi_finish_request(). There's not much documentation for this particular function, however.
The point of fastcgi_finish_request() seems to be to flush all data and proceed with other tasks, but what I want to achieve, as would normally work with register_shutdown_function(), is basically to put the contents of the output buffer into a file without the user having to wait for this to finish.
Is there any way to achieve this under PHP-FPM, with fastcgi_finish_request() or another function?
$timeout = 3600; // cache time-out
$file = '/home/example.com/public_html/cache/' . md5($_SERVER['REQUEST_URI']); // unique id for this page
if (file_exists($file) && (filemtime($file) + $timeout) > time()) {
readfile($file);
exit();
} else {
ob_start();
register_shutdown_function(function () use ($file) {
// sleep(5);
$content = ob_get_flush();
file_put_contents($file, $content);
});
}

Answer 1

Yes, it's possible to use fastcgi_finish_request for that. You can save this file and see that it works:
<?php
$timeout = 3600; // cache time-out
$file = '/home/galymzhan/www/ps/' . md5($_SERVER['REQUEST_URI']); // unique id for this page
if (file_exists($file) && (filemtime($file) + $timeout) > time()) {
echo "Got this from cache<br>";
readfile($file);
exit();
} else {
ob_start();
echo "Content to be cached<br>";
$content = ob_get_flush();
fastcgi_finish_request();
// sleep(5);
file_put_contents($file, $content);
}
Even if you uncomment the line with sleep(5), you'll see that page still opens instantly because fastcgi_finish_request sends data back to browser and then proceeds with whatever code is written after it.

Answer 2

First of all,
If you cache the dynamic content this way, you're doing it wrong. Surely it can be used this way and it will be able to work, but its totally paralyzed by the approach itself.
if you want to efficiently cache and handle content, create one class and wrap all caching function into.
Yes, you can use fast_cgi_finish_request() like a register_shutdown(). The only difference is that, fast_cgi_finish_request() will send an output(if any) and WILL NOT TERMINATE the script, while an callback of register_shutdown() will be invoked on script termination.

Answer 3

This is an old question, but I don't think any of the answers correctly answer the problem.
As I understand it, the problem is that none of the output gets sent to the client until the ob_get_flush() call that happens during the shutdown function.
To fix that issue, you need to pass a function and a chunk size to ob_start() in order to handle the output in chunks.
Something like this for your else clause:
$content = '';
$write_buffer_func = function($buffer, $phase) use ($file, &$content) {
$content .= $buffer;
if ($phase & PHP_OUTPUT_HANDLER_FINAL) {
file_put_contents($file, $content);
}
return $buffer;
};
ob_start($write_buffer_func, 1024);