Last updated: Fri, 10 Oct 2008

curl_multi_exec

(PHP 5)

curl_multi_exec — Run the sub-connections of the current cURL handle

Description

int curl_multi_exec ( resource $mh , int &$still_running )

Processes each of the handles in the stack. This method can be called whether or not a handle needs to read or write data.

Parameters

mh: A cURL multi handle returned by curl_multi_init().
still_running: A reference to a flag to tell whether the operations are still running.

Return Values

A cURL code defined in the cURL Predefined Constants.

Note: This only returns errors regarding the whole multi stack. There might still have occurred problems on individual transfers even when this function returns CURLM_OK.

Examples

Example #1 curl_multi_exec() example

This example will create two cURL handles, add them to a multi handle, and then run them in parallel.


<?php
// create both cURL resources
$ch1 = curl_init();
$ch2 = curl_init();

// set URL and other appropriate options
curl_setopt($ch1, CURLOPT_URL, "http://lxr.php.net/");
curl_setopt($ch1, CURLOPT_HEADER, 0);
curl_setopt($ch2, CURLOPT_URL, "http://www.php.net/");
curl_setopt($ch2, CURLOPT_HEADER, 0);

//create the multiple cURL handle
$mh = curl_multi_init();

//add the two handles
curl_multi_add_handle($mh,$ch1);
curl_multi_add_handle($mh,$ch2);

$active = null;
//execute the handles
do {
    $mrc = curl_multi_exec($mh, $active);
} while ($mrc == CURLM_CALL_MULTI_PERFORM);

while ($active && $mrc == CURLM_OK) {
    if (curl_multi_select($mh) != -1) {
        do {
            $mrc = curl_multi_exec($mh, $active);
        } while ($mrc == CURLM_CALL_MULTI_PERFORM);
    }
}

//close the handles
curl_multi_remove_handle($mh, $ch1);
curl_multi_remove_handle($mh, $ch2);
curl_multi_close($mh);

?>


> replying to viczbk.ru



Just sharing my attempt at it.



> while (($res = curl_multi_select($mh)) === 0) {};

This worked on my windows computer (php 5.2.5) but when I ran the curl program in my new centOS server (php 5.1.6) the function never updates unless curl_multi_exec() is added to the loop, taking away the point of using it to save cycles. curl_multi_select() also allows you to set a timeout but it doesn't seem to help, then again, don't see why people wouldn't use it anyway.



Even when curl_multi_select($mh) does work there's no way to know which of the sockets updated in status or if they've received partial data, completely finished, or just timed out. It's not reliable if you want to remove / add data as soon as things finish. Try calling just example.com or some other website with very little data. curl_multi_select($mh) can send non 0 value a couple of thousand times before finishing. Lazily adding a usleep(25000) or some minimal amount can also help not waste cycles.

viczbk.ru
08-Feb-2008 11:04


http://curl.haxx.se/libcurl/c/libcurl-multi.html



"When you've added the handles you have for the moment (you can still add new ones at any time), you start the transfers by call curl_multi_perform(3).



curl_multi_perform(3) is asynchronous. It will only execute as little as possible and then return back control to your program. It is designed to never block. If it returns CURLM_CALL_MULTI_PERFORM you better call it again soon, as that is a signal that it still has local data to send or remote data to receive."



So it seems the loop in sample script should look this way:



<?php

$running=null;

//execute the handles

do {

    while (CURLM_CALL_MULTI_PERFORM === curl_multi_exec($mh, $running));

    if (!$running) break;

    while (($res = curl_multi_select($mh)) === 0) {};

    if ($res === false) {

        echo "<h1>select error</h1>";

        break;

    }

} while (true);

?>



This worked fine (PHP 5.2.5 @ FBSD 6.2) without running non-blocked loop and wasting CPU time.



However this seems to be the only use of curl_multi_select, coz there's no simple way to bind it with other PHP wrappers for select syscall.

robert dot reichel at boboton dot com
20-Oct-2007 08:54


I was testing PHP code provided by dtorop933@gmail.com in curl_multi_exec section of PHP Manual.



The part of the code '$err = curl_error($conn[$i])' should return error message for each cURL session, but it does not.

The function curl_error() works well with the curl_exec(). Is there any other solution for getting session error message with curl_multi_exec() or there is a bug in cURL library.



The script was tested with Windows XP and PHP-5.2.4

shichuanr at gmail dot com
06-Sep-2007 08:12


For people who have problem running the above example script(Example 425. curl_multi_exec()), you can alter it a little bit to make it work properly by replacing the existing chunk of code with the one below: 



<?php

// create both cURL resources

$ch1 = curl_init();

$ch2 = curl_init();



// set URL and other appropriate options

curl_setopt($ch1, CURLOPT_URL, "http://www.google.com/");

curl_setopt($ch1, CURLOPT_HEADER, 0);

curl_setopt($ch2, CURLOPT_URL, "http://www.php.net/");

curl_setopt($ch2, CURLOPT_HEADER, 0);



//create the multiple cURL handle

$mh = curl_multi_init();



//add the two handles

curl_multi_add_handle($mh,$ch1);

curl_multi_add_handle($mh,$ch2);



$running=null;

//execute the handles

do {

    curl_multi_exec($mh,$running);

} while ($running > 0);

//close the handles

curl_multi_remove_handle($mh,$ch1);

curl_multi_remove_handle($mh,$ch1);

curl_multi_close($mh);



?>

substr("iscampifriese",1,11) dot " at beer dot com"
04-Jul-2007 09:10


If you are using mulit handles and you wish to re-execute any of them (if they timed out or something), then you need to remove the handles from the mulit-handle and then re-add them in order to get them to re-execute.  Otherwise cURL will just give you back the same results again without actually retrying.

add a note

curl_multi_getcontent

curl_multi_close