curl_multi_select

(PHP 5, PHP 7, PHP 8)

curl_multi_select — 任意の cURL マルチハンドル接続で読み取りまたは書き込みが可能になるまで待機する

説明

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

スクリプトの実行をブロックし、次の curl_multi_exec() の呼び出しで cURL マルチハンドルに関連付けられた cURL ハンドルが処理を進められるようになるか、タイムアウトになるまで待機します（どちらか早い方が適用されます）。

パラメータ

multi_handle: curl_multi_init() が返す cURL マルチハンドル。
timeout: アクティブな cURL マルチハンドル接続からのレスポンスを待機する時間（秒単位）。

戻り値

成功した場合は、記述子セットに含まれるアクティブな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() システムコールから) select に失敗した場合は -1 を返します。

エラー / 例外

timeout が 0 未満または PHP_INT_MAX を超える場合、ValueError をスローします。

変更履歴

バージョン	説明
8.4.0	`timeout` が `0` 未満または `PHP_INT_MAX` を超える場合、ValueError をスローするようになりました。
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 ¶

3 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 ¶

12 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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