Demonstration of process forking in PHP to speed up image resizing

multi-process.php

<?php

/**
 * Create a thumbnail image from the specified file
 * 
 * @param int $height output image height
 * @param int $width  output image width
 */

function create_preview($height, $width)
{
    //Input image
    $img = 'test.jpg';
    
    //Output image
    $new_img = 'test -'.$width.'x'.$height.'.jpg';
    
    //get the current image size
    list($full_width, $full_height) = getimagesize($img) ;

    //Create a blank image to load in the new resized image
    $tn = imagecreatetruecolor($width, $height) ;

    //Load the original file
    $image = imagecreatefromjpeg($img) ;

    //Do the crop
    imagecopyresampled($tn, $image, 0, 0, 0, 0, $width, $height, $full_width, $full_height) ;

    //Save the file
    imagejpeg($tn, $new_img, 100);
}        
       
// The thumbnail sizes to be generated
$image_sizes = array(
    array(100,100),
    array(200, 200),
    array(300, 300),
    array(400, 400),
    array(500, 500),
    array(1000, 1000)
);


//Counter for number of processes
$i = 1;

//Loop through the image sizes but this time fork a process for each size.
foreach($image_sizes as $image_size)
{
    //Fork a process
    $pid = pcntl_fork();
    
    //if we're in a child thread then grab an image size and process it.
    if (!$pid)
    {
        echo 'starting child ', $i, PHP_EOL;
        create_preview($image_size[0], $image_size[1]);
        
        //Die otherwise the process will continue to loop and each process will 
        //create all the thumbnails
        die();
    }
    
    $i++;
}

//Wait for all the subprocesses to complete to avoid zombie processes
foreach($image_sizes as $image_size)
{
    pcntl_wait($status);
}

?>

single-process.php

<?php

/**
 * Create a thumbnail image from the specified file
 * 
 * @param int $height output image height
 * @param int $width  output image width
 */

function create_preview($height, $width)
{
    //Input image
    $img = 'test.jpg';
    
    //Output image
    $new_img = 'test -'.$width.'x'.$height.'.jpg';
    
    //get the current image size
    list($full_width, $full_height) = getimagesize($img) ;

    //Create a blank image to load in the new resized image
    $tn = imagecreatetruecolor($width, $height) ;

    //Load the original file
    $image = imagecreatefromjpeg($img) ;

    //Do the crop
    imagecopyresampled($tn, $image, 0, 0, 0, 0, $width, $height, $full_width, $full_height) ;

    //Save the file
    imagejpeg($tn, $new_img, 100);
}        

// The thumbnail sizes to be generated
$image_sizes = array(
    array(100,100),
    array(200, 200),
    array(300, 300),
    array(400, 400),
    array(500, 500),
    array(1000, 1000)
);

// Loop through the images sequentially
foreach($image_sizes as $image_size)
{
    create_preview($image_size[0], $image_size[1]);
}

?>