note 108928 modified in function.curl-multi-select by danbrown

curl_multi_select($mh, $timeout) simply blocks for $timeout seconds while curl_multi_exec() returns CURLM_CALL_MULTI_PERFORM. Otherwise, it works as intended, and blocks until at least one connection has completed or $timeout seconds, whatever happens first.

For that reason, curl_multi_exec() should always be wrapped:

<?php
 function full_curl_multi_exec($mh, &$still_running) {
 do {
 $rv = curl_multi_exec($mh, $still_running);
 } while ($rv == CURLM_CALL_MULTI_PERFORM);
 return $rv;
 }
?>

With that, the core of "multi" processing becomes (ignoring error handling for brevity):

<?php
 full_curl_multi_exec($mh, $still_running); // start requests
 do { // "wait for completion"-loop
 curl_multi_select($mh); // non-busy (!) wait for state change
 full_curl_multi_exec($mh, $still_running); // get new state
 while ($info = curl_multi_info_read($mh)) {
 // process completed request (e.g. curl_multi_getcontent($info['handle']))
 }
 } while ($still_running);
?>

Note that after starting requests, retrieval is done in the background - one of the better shots at parallel processing in PHP. --was-- curl_multi_select($mh, $timeout) simply blocks for $timeout seconds while curl_multi_exec() returns CURLM_CALL_MULTI_PERFORM. Otherwise, it works as intended, and blocks until at least one connection has completed or $timeout seconds, whatever happens first. For that reason, curl_multi_exec() should always be wrapped: function full_curl_multi_exec($mh, &$still_running) { do { $rv = curl_multi_exec($mh, $still_running); } while ($rv == CURLM_CALL_MULTI_PERFORM); return $rv; } With that, the core of "multi" processing becomes (ignoring error handling for brevity): full_curl_multi_exec($mh, $still_running); // start requests do { // "wait for completion"-loop curl_multi_select($mh); // non-busy (!) wait for state change full_curl_multi_exec($mh, $still_running); // get new state while ($info = curl_multi_info_read($mh)) { // process completed request (e.g. curl_multi_getcontent($info['handle'])) } } while ($still_running); Note that after starting requests, retrieval is done in the background - one of the better shots at parallel processing in PHP. http://php.net/manual/en/function.curl-multi-select.php