Make sure imagepng has written the file on the server - php

Question

I have a function which adds text under a existing qr-code image.
In some cases the return is faster than the server has written the image on the filesystem, so that other function got issues.
How can I make sure that everything is done before I return the path to the image?
At the moment I am trying to use a while-loop, but I am also really unhappy with it. That causes also timeouts and crashes on my server (no idea why).
function addTextToQrCode($oldImage, $text)
{
$newImage = $oldImage;
$newImage = str_replace(".png", "_original.png", $newImage);
copy($oldImage, $newImage);
$image = imagecreatefrompng($oldImage);
$black = imagecolorallocate($image, 0, 0, 0);
$fontSize = 20;
$textWidth = imagefontwidth($fontSize) * strlen($text);
$textHeight = imagefontheight($fontSize);
$x = imagesx($image) / 2 - $textWidth / 2;
$y = imagesy($image) - $textHeight - 3;
imagestring($image, 5, $x, $y, $text, $black);
$filePath = "/qrCodes/qrcode".$text.'.png';
imagepng($image, $filePath);
while(!$this->checkIfNewQrCodeIsOnFileSystem($filePath)){
$this->checkIfNewQrCodeIsOnFileSystem($filePath);
}
return $filePath;
}
function checkIfNewQrCodeIsOnFileSystem($filePath) {
if (file_exists($filePath)) {
return true;
} else {
return false;
}
}

Answer 1

Check only imagepng(). The solution i would prefer.
function addTextToQrCode($oldImage, $text)
{
$newImage = $oldImage;
$newImage = str_replace(".png", "_original.png", $newImage);
copy($oldImage, $newImage);
$image = imagecreatefrompng($oldImage);
$black = imagecolorallocate($image, 0, 0, 0);
$fontSize = 20;
$textWidth = imagefontwidth($fontSize) * strlen($text);
$textHeight = imagefontheight($fontSize);
$x = imagesx($image) / 2 - $textWidth / 2;
$y = imagesy($image) - $textHeight - 3;
imagestring($image, 5, $x, $y, $text, $black);
$filePath = "/qrCodes/qrcode".$text.'.png';
if (imagepng($image, $filePath) === true) {
return $filePath;
}
}