在图像调整大小脚本（GD）期间释放内存

Question

I have the following code that takes $_POST ed images from a HTML <form> and uploads them. It then re-sizes them all (up to twice) and saves these smaller images to the same directory.

However, I am running out of memory when dealing with larger files.

My question is not "how do I prevent X error from occuring?", but "How do I free up memory this script is using so it can continue?"

<?php
if (!isset($_POST['SiteID']) || !filter_var($_POST['SiteID'], FILTER_VALIDATE_INT)) {
    header("Location: ./");
    exit();
}
$SiteID = $_POST['SiteID'];

if (!isset($_POST['GalleryID']) || !filter_var($_POST['GalleryID'], FILTER_VALIDATE_INT)) {
    header("Location: ./?SiteID=" . $SiteID . "&error=upload");
    exit();
}
$GalleryID = $_POST['GalleryID'];

$ImageFile = $_FILES['ImageFile'];

$Extensions = array("jpg", "jpeg");
$Timestamp = date("U");

require_once("db.php");

for ($X = 0; $X < count($_FILES['ImageFile']['name']); $X++) {
    $Extension = strtolower(pathinfo($ImageFile['name'][$X], PATHINFO_EXTENSION));
    if (in_array($Extension, $Extensions)) {
        if ($ImageFile['error'][$X] === UPLOAD_ERR_OK) {
            if ($ImageFile['size'][$X] <= 5 * 1024 * 1024) {
                $Filename = $GalleryID . "-" . $Timestamp . "-" . $X . "." . $Extension;
                move_uploaded_file($ImageFile['tmp_name'][$X], "uploads/" . $Filename);
                mysql_query("INSERT INTO NewGalleryImages SET GalleryID = $GalleryID, ImageFile = '$Filename', ImageCaption = ''");
                $Dimensions = getimagesize("uploads/" . $Filename);
                $Width = ($Dimensions[0] > 768 ? 768 : $Dimensions[0]);
                $Height = ($Dimensions[1] / $Dimensions[0]) * $Width;
                $Expl = explode(".", $Filename);
                $LargeFilename = $Expl[0] . "_gallery." . $Expl[1];
                $Source = "uploads/" . $Filename;
                $Canvas = imagecreatetruecolor($Width, $Height);
                $LargeImage = imagecreatefromjpeg($Source);
                imagecopyresampled($Canvas, $LargeImage, 0, 0, 0, 0, $Width, $Height, $Dimensions[0], $Dimensions[1]);
                imagejpeg($Canvas, "uploads/" . $LargeFilename, 100);
                imagedestroy($Canvas);
                $Width = 200;
                $Height = ($Dimensions[1] / $Dimensions[0]) * $Width;
                $Expl = explode(".", $Filename);
                $ThumbFilename = $Expl[0] . "_thumb." . $Expl[1];
                $Source = "uploads/" . $Filename;
                $Canvas = imagecreatetruecolor($Width, $Height);
                $ThumbImage = imagecreatefromjpeg($Source);
                imagecopyresampled($Canvas, $ThumbImage, 0, 0, 0, 0, $Width, $Height, $Dimensions[0], $Dimensions[1]);
                imagejpeg($Canvas, "uploads/" . $ThumbFilename, 100);
                imagedestroy($Canvas);
            } else {
                mysql_close();
                header("Location: ./?SiteID=" . $SiteID . "&error=size");
                exit();
            }
        } else {
            mysql_close();
            header("Location: ./?SiteID=" . $SiteID . "&error=unknown");
            exit();
        }
    } else {
        mysql_close();
        header("Location: ./?SiteID=" . $SiteID . "&error=type");
        exit();
    }
}

mysql_close();
header("Location: ./?SiteID=" . $SiteID . "&uploaded");
exit();

// var_dump($_POST);
// var_dump($_FILES);
// var_dump($ImageFile);
?>

I read about imagedestroy() in the PHP documentation, and have tried adding that in to my script in a couple of places, but 1) I'm not sure I'm destroying the right resource, and 2) I'm not sure it's actually clearing the memory.

I currently have the following setting on the server:

post_max_size = 64M
upload_max_filesize = 10M
max_input_time = 60
max_input_nesting_level = 64
max_execution_time = 120
memory_limit = 512M
max_input_vars = 1000

And this is the error message I am receiving:

Fatal error: Allowed memory size of 536870912 bytes exhausted
(tried to allocate 29440 bytes) in
/var/www/vhosts/example.com/httpsdocs/gallery-upload.php
on line 36

What I find odd is, no matter how much I increate the memory_limit to, the "extra" it needs to allocate is always the same: 29440 bytes .

If I upload images individually, the script runs okay, but uploading more than two at a time throws the error. More than 512MB of memory to resize two images seems excessive, no? Or is it still not enough memory? I'm not sure how much this server can spare...! How can I reduce my total memory usage?

Answer 1

After a little bit of playing about, I've managed to get my script to work. What I needed to do was use imagedestroy() on both the new image, and the original image after each resize, ie:

imagedestroy($LargeImage);
imagedestroy($Canvas);

I'm not sure if this is everything that could be done to free up memory, but it's working (for now). I'm sure someone will test my memory limits again with an even larger image file soon...