do while loop causing 100% CPU usage with curl_multi_exec

Question

This is a loop used in our script with curl. It's causing CPU usage to shoot up to 100%. A friend said "Your computer is looping so fast here it doesn't have time to process the request since it is constantly checking for a finish."... So my question is how can this loop be re-written to slow down? Thanks

$running = null;
do {
  curl_multi_exec($mh, $running);
} while($running > 0);

Answer 1

Try this: http://php.net/manual/function.curl-multi-select.php

Answer 2

Adding a call to http://php.net/sleep or http://php.net/usleep in every iteration should reduce the CPU usage by allowing other running processes to be scheduled by the operating system.

Answer 3

Unfortunately you didn't post whole code. I suppose you are doing something like

$mh = curl_multi_init();
for ($i = 0; $i < $desiredThreadsNumber; $i++) {
    $ch = curl_init();
    // set up $ch here
    curl_multi_add_handle($mh, $ch);
}

You should understand that you haven't run threads yet here. curl_multi_exec() runs all threads. But it can't run all $desiredThreadsNumber threads simultaneously. If you look on example on curl_multi_exec() php.net page, you will see that you must wait while curl_multi_exec() run all threads. In other words, you need next nested loop here:

$running = null;
do {
    do {
        $mrc = curl_multi_exec($mh, $running);
    } while ($mrc == CURLM_CALL_MULTI_PERFORM);
} while($running > 0);

At the end let me suggest you to read this article http://www.onlineaspect.com/2009/01/26/how-to-use-curl_multi-without-blocking/ and use code snippet from there, I used it in 2 or 3 projects.