curl_multi_select

(PHP 5, PHP 7, PHP 8)

curl_multi_select — curl_multi 接続のアクティビティを待つ

説明

curl_multi_select(CurlMultiHandle $multi_handle, float $timeout = 1.0): int

curl_multi 接続に関するアクティビティがあるまでブロックします。

パラメータ

multi_handle: curl_multi_init() が返す cURL マルチハンドル。
timeout: レスポンスを待つ秒数。

戻り値

成功した場合は、記述子セットに含まれる記述子の数を返します。どの記述子上にもアクティビティがなかった場合は、結果が 0 になることもあります。 select に失敗した場合は -1 を返し、それ以外の失敗時は (select システムコールから) タイムアウトします。

変更履歴

バージョン	説明
8.0.0	`multi_handle` は CurlMultiHandle クラスのインスタンスを期待するようになりました。これより前のバージョンでは、resource を期待していました。

参考

curl_multi_init() - 新規 cURL マルチハンドルを返す

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User Contributed Notes 8 notes

down

nevil85 at gmail dot com ¶

10 years ago

Even after so many distro releases, in PHP v5.5.9 and libcurl v7.35.0, curl_multi_select still returns -1. The only work around here is to wait and proceed like nothing ever happened. You have to determine the "wait" required here. 

In my application a very small interval like usleep(1) worked. For example:

<?php
        // While we're still active, execute curl
        $active = null;
        do {
            $mrc = curl_multi_exec($multi, $active);
        } while ($mrc == CURLM_CALL_MULTI_PERFORM);
    
        while ($active && $mrc == CURLM_OK) {
            // Wait for activity on any curl-connection
            if (curl_multi_select($multi) == -1) {
                usleep(1);
            }
    
            // Continue to exec until curl is ready to
            // give us more data
            do {
                $mrc = curl_multi_exec($multi, $active);
            } while ($mrc == CURLM_CALL_MULTI_PERFORM);
        }
?>

Internally php curl_multi_select uses libcurl curl_multi_fdset function and its libcurl documentation says :
http://curl.haxx.se/libcurl/c/curl_multi_fdset.html

"When libcurl returns -1 in max_fd, it is because libcurl currently does something that isn't possible for your application to monitor with a socket and unfortunately you can then not know exactly when the current action is completed using select(). When max_fd returns with -1, you need to wait a while and then proceed and call curl_multi_perform anyway. How long to wait? I would suggest 100 milliseconds at least, but you may want to test it out in your own particular conditions to find a suitable value. 

When doing select(), you should use curl_multi_timeout to figure out how long to wait for action."

Untill PHP implements curl_multi_timeout() we have to play with our application and determine the "wait".

down

bishop at php dot net ¶

5 years ago

Before PHP 7.1.23 and 7.2.11, curl_multi_select() would return -1 if cURL had no open file descriptors. Since then, assuming libcurl 7.28 or higher, curl_multi_select() will return 0 if cURL has no open file descriptors and -1 on error.



See https://bugs.php.net/bug.php?id=76480



This is a BC break. See https://bugs.php.net/bug.php?id=77030

down

vigo dot von dot harrach at gmx dot de ¶

12 years ago

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.

down

public at grik dot net ¶

16 years ago

This function blocks the calling process until there is activity on any of the connections opened by the curl_multi interface, or until the timeout period has expired. 
In other words, it waits for data to be received in the opened connections.

Internally it fetches socket pointers with "curl_multi_fdset()" and runs the "select()" C function.
It returns in 3 cases:
1. Activity is detected on any socket;
2. Timeout has ended (second parameter);
3. Process received any signal (#man kill).

The function returns an integer:
* In case of activity it returns a number, usually 1.
I suppose, it returns the number of connections with activity detected.
* If timeout expires it returns 0
* In case of error it returns -1

Thanks for attention, hope this helps.

down

xxavalanchexx at gmail dot com ¶

10 years ago

According to https://bugs.php.net/bug.php?id=61141:

On Windows setups using libcurl version 7.24 or later (which seems to correspond to PHP 5.3.10 or later), you may find that this always returns -1. This is, apparently, not strictly a bug: according to the libcurl documentation, you should add your own sleep if curl_multi_select returns -1.

For example:
<?php
/* setup $mh */

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

while ($active && $mrc == CURLM_OK) {
    if (curl_multi_select($mh) == -1) {
        usleep(100);
    }
    do {
        $mrc = curl_multi_exec($mh, $active);
    } while ($mrc == CURLM_CALL_MULTI_PERFORM);
}

/* close $mh */
?>

down

Anonymous ¶

11 years ago

In 5.3.9+, curl_multi_select always returns -1. If this is your case, just wait a bit and then proceed like nothing ever happened:
<?php
do {  
    $mrc = curl_multi_exec($multi, $active);  
} while ($mrc == CURLM_CALL_MULTI_PERFORM);  
    
while ($active && $mrc == CURLM_OK) {
    //check for results and execute until everything is done

    if (curl_multi_select($multi) == -1) {
        //if it returns -1, wait a bit, but go forward anyways!
        usleep(100); 
    }
    
    //do something with the return values
    while(($info = curl_multi_info_read($multi)) !== false){
        if ($info["result"] == CURLE_OK){
            $content = curl_multi_getcontent($info["handle"]);
            do_something($content);
        }
    }
    do {  
        $mrc = curl_multi_exec($multi, $active);  
    } while ($mrc == CURLM_CALL_MULTI_PERFORM);          
}
?>

down

gib-o-master ¶

2 years ago

NOTE: current implementation of `curl_multi_select` doesn't block and doesn't respect timeout parameter (maybe will be fixed later, in this case just remove the usleep call)

here, i would like to post my working/tested example of proper usage of this function:

```
$running  = 1;
while ($running)
{
  # execute request
  if ($a = curl_multi_exec($this->murl, $running)) {
    throw BotError::text("curl_multi_exec[$a]: ".curl_multi_strerror($a));
  }
  # check finished
  if (!$running) {
    break;
  }
  # wait for activity
  while (!$a)
  {
    if (($a = curl_multi_select($this->murl, $timeout)) < 0)
    {
      throw BotError::text(
        ($a = curl_multi_errno($this->murl))
          ? "curl_multi_select[$a]: ".curl_multi_strerror($a)
          : 'system select failed'
      );
    }
    usleep($timeout * 1000000);# should be <=1
  }
}
```

down

Alex Palmer ¶

11 years ago

On php 5.3.18+ be aware that curl_multi_select() may return -1 forever until you call curl_multi_exec().
See https://bugs.php.net/bug.php?id=63411 for more information.

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