Multiple request in curl function - php

Question

i am just transloading multiple files from one server to another, if it comes less then this script work perfect, if its crossing to thousands URL's then requests increase and then server block for accessing files.
Here is script
<?php
// Check if form has been submitted
if(#$_POST['submit']){
ini_set("max_execution_time", 0); // no time-outs!
ignore_user_abort(true); // Continue downloading even after user closes the browser.
// URLS -- One on each line
$URL = $_POST['url'];
// Relative path to Save downloaded images
// Default is "downloads"
// Make sure that it is writable (chmoded correctly)
$folder = $_POST['folder'];
// Check if User has provided a local folder
if (!$folder || !isset($folder)){
// Generate error if left blank by user.
die ("Please specify local folder name");
}
// Split all URLS into an array
$urls = split("\n", $URL);
// Remove Carriage Returns (useful for Windows-based browsers)
$urls = str_replace("\r", "", $urls);
$mh = curl_multi_init();
foreach ($urls as $i => $url) {
$path = pathinfo($url);
$g=$folder . "/" . $path["basename"] ;
// Check if file already exists on local folder.
if(file_exists($g)){
// If exists, delete the file so it always contains the latest update.
unlink($g) or die("Unable to delete existing '$g'!");
}
// Update the user of what's going on
echo "$i) Downloading: from <b>$url</b> to <b>$g</b><br />";
if(!is_file($g)){
$conn[$i]=curl_init($url);
$fp[$i]=fopen ($g, "w");
curl_setopt ($conn[$i], CURLOPT_FILE, $fp[$i]);
curl_setopt ($conn[$i], CURLOPT_HEADER ,0);
// curl_setopt($conn[$i],CURLOPT_CONNECTTIMEOUT,1000);
curl_multi_add_handle ($mh,$conn[$i]);
}
}
do {
$n=curl_multi_exec($mh,$active);
}
while ($active);
foreach ($urls as $i => $url) {
curl_multi_remove_handle($mh,$conn[$i]);
curl_close($conn[$i]);
fclose ($fp[$i]);
}
curl_multi_close($mh);
} // task closed
?>
<br />
<br />
<fieldset>
<legend>
<label for="url">Server to Server Upload Script</label>
</legend>
<form method=POST>
<label for="url">Insert Files URL, One Per Line: </label><br />
<textarea rows=15 cols=75 id="url" name="url"><?= $URL ?></textarea><br />
<label for="folder">Folder Name: </label><input type=text id="folder" name="folder" value="uploads"/>
<input type=submit name="submit" value="Start Uploading Files!" />
</form>
</fieldset>
With this script if i add 5000 URL's it suddenly starts sending request and transloading the files. (Server block it due to huge requests.)
How do i add code once the first file transloaded then the other
request should be sent. ?