Multi-threading a for statement with php - php

Question

I'm using this following function to check if images exist at their location. Each time the script runs it load about 40 - 50 urls and so its taking long time to load the page. I was thinking of using threading for the "for statement" (at the end of the script) but couldn't find many examples on how to do that. I'm not very familiar with multi-threading with php but i found an example here using popen.
My script:
function get_image_dim($sURL) {
try {
$hSock = # fopen($sURL, 'rb');
if ($hSock) {
while(!feof($hSock)) {
$vData = fread($hSock, 300);
break;
}
fclose($hSock);
if (strpos(' ' . $vData, 'JFIF')>0) {
$vData = substr($vData, 0, 300);
$asResult = unpack('H*',$vData);
$sBytes = $asResult[1];
$width = 0;
$height = 0;
$hex_width = '';
$hex_height = '';
if (strstr($sBytes, 'ffc2')) {
$hex_height = substr($sBytes, strpos($sBytes, 'ffc2') + 10, 4);
$hex_width = substr($sBytes, strpos($sBytes, 'ffc2') + 14, 4);
} else {
$hex_height = substr($sBytes, strpos($sBytes, 'ffc0') + 10, 4);
$hex_width = substr($sBytes, strpos($sBytes, 'ffc0') + 14, 4);
}
$width = hexdec($hex_width);
$height = hexdec($hex_height);
return array('width' => $width, 'height' => $height);
} elseif (strpos(' ' . $vData, 'GIF')>0) {
$vData = substr($vData, 0, 300);
$asResult = unpack('h*',$vData);
$sBytes = $asResult[1];
$sBytesH = substr($sBytes, 16, 4);
$height = hexdec(strrev($sBytesH));
$sBytesW = substr($sBytes, 12, 4);
$width = hexdec(strrev($sBytesW));
return array('width' => $width, 'height' => $height);
} elseif (strpos(' ' . $vData, 'PNG')>0) {
$vDataH = substr($vData, 22, 4);
$asResult = unpack('n',$vDataH);
$height = $asResult[1];
$vDataW = substr($vData, 18, 4);
$asResult = unpack('n',$vDataW);
$width = $asResult[1];
return array('width' => $width, 'height' => $height);
}
}
} catch (Exception $e) {}
return FALSE;
}
for($y=0;$y<= ($image_count-1);$y++){
$dim = get_image_dim($images[$y]);
if (empty($dim)) {
echo $images[$y];
unset($images[$y]);
}
}
$images = array_values($images);
The popen example i found was:
for ($i=0; $i<10; $i++) {
// open ten processes
for ($j=0; $j<10; $j++) {
$pipe[$j] = popen('script.php', 'w');
}
// wait for them to finish
for ($j=0; $j<10; ++$j) {
pclose($pipe[$j]);
}
}
I'm not sure which part of my code has to go in the script.php? I tried moving the whole script but that didn't work?
Any ideas on how can i implement this or if there is a better way to multi thread it? Thanks.

Answer 1

PHP does not have multi-threading natively. You can do it with pthreads, but having a little experience there, I can say with assurance that that is too much for your needs.
Your best bet will be to use curl, you can initiate multiple requests with curl_multi_init. Based off the example on PHP.net, the following may work for your needs:
function curl_multi_callback(Array $urls, $callback, $cache_dir = NULL, $age = 600) {
$return = array();
$conn = array();
$max_age = time()-intval($age);
$mh = curl_multi_init();
if(is_dir($cache_dir)) {
foreach($urls as $i => $url) {
$cache_path = $cache_dir.DIRECTORY_SEPARATOR.sha1($url).'.ser';
if(file_exists($cache_path)) {
$stat = stat($cache_path);
if($stat['atime'] > $max_age) {
$return[$i] = unserialize(file_get_contents($cache_path));
unset($urls[$i]);
} else {
unlink($cache_path);
}
}
}
}
foreach ($urls as $i => $url) {
$conn[$i] = curl_init($url);
curl_setopt($conn[$i], CURLOPT_RETURNTRANSFER, 1);
curl_multi_add_handle($mh, $conn[$i]);
}
do {
$status = curl_multi_exec($mh, $active);
// Keep attempting to get info so long as we get info
while (($info = curl_multi_info_read($mh)) !== FALSE) {
// We received information from Multi
if (false !== $info) {
// The connection was successful
$handle = $info['handle'];
// Find the index of the connection in `conn`
$i = array_search($handle, $conn);
if($info['result'] === CURLE_OK) {
// If we found an index and that index is set in the `urls` array
if(false !== $i && isset($urls[$i])) {
$content = curl_multi_getcontent($handle);
$return[$i] = $data = array(
'url' => $urls[$i],
'content' => $content,
'parsed' => call_user_func($callback, $content, $urls[$i]),
);
if(is_dir($cache_dir)) {
file_put_contents($cache_dir.DIRECTORY_SEPARATOR.sha1($urls[$i]).'.ser', serialize($data));
}
}
} else {
// Handle failures how you will
}
// Close, even if a failure
curl_multi_remove_handle($mh, $handle);
unset($conn[$i]);
}
}
} while ($status === CURLM_CALL_MULTI_PERFORM || $active);
// Cleanup and resolve any remaining connections (unlikely)
if(!empty($conn)) {
foreach ($conn as $i => $handle) {
if(isset($urls[$i])) {
$content = curl_multi_getcontent($handle);
$return[$i] = $data = array(
'url' => $urls[$i],
'content' => $content,
'parsed' => call_user_func($callback, $content, $urls[$i]),
);
if(is_dir($cache_dir)) {
file_put_contents($cache_dir.DIRECTORY_SEPARATOR.sha1($urls[$i]).'.ser', serialize($data));
}
}
curl_multi_remove_handle($mh, $handle);
unset($conn[$i]);
}
}
curl_multi_close($mh);
return $return;
}
$return = curl_multi_callback($urls, function($data, $url) {
echo "got $url\n";
return array('some stuff');
}, '/tmp', 30);
//print_r($return);
/*
$url_dims = array(
'url' => 'http://www......',
'content' => raw content
'parsed' => return of get_image_dim
)
*/
Just restructure your original function get_image_dim to consume the raw data and output whatever you are looking for.
This is not a complete function, there may be errors, or idiosyncrasies you need to resolve, but it should serve as a good starting point.
Updated to include caching. This changed a test I was running on 18 URLS from 1 second, to .007 seconds (with cache hits).
Note: you may want to not cache the full request contents, as I did, and just cache the url and the parsed data.