PHP: Send response and continue processing

respond_and_process.php

<?php

// Buffer all upcoming output...
ob_start();

// Send your response.
echo "Testing response";

// Get the size of the output.
$size = ob_get_length();

// Disable compression (in case content length is compressed).
header("Content-Encoding: none");

// Set the content length of the response.
header("Content-Length: {$size}");

// Close the connection.
header("Connection: close");

// Flush all output.
ob_end_flush();
ob_flush();
flush();

// Close current session (if it exists).
if (session_id()) {
    session_write_close();
}

sleep(30);
file_put_contents('/tmp/foo', 'testing');