PHP的curl_multi系列函数，在官方文档中，看到了两种代码写法：

第一种

// 创建一对cURL资源
$ch1 = curl_init();
$ch2 = curl_init();

// 设置URL和相应的选项
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);

// 创建批处理cURL句柄
$mh = curl_multi_init();

// 增加2个句柄
curl_multi_add_handle($mh,$ch1);
curl_multi_add_handle($mh,$ch2);

$active = null;
// 执行批处理句柄
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);
    }
}

// 关闭全部句柄
curl_multi_remove_handle($mh, $ch1);
curl_multi_remove_handle($mh, $ch2);
curl_multi_close($mh);

?>

第二种

<?php
// 创建一对cURL资源
$ch1 = curl_init();
$ch2 = curl_init();

// 设置URL和相应的选项
curl_setopt($ch1, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch1, CURLOPT_HEADER, 0);
curl_setopt($ch2, CURLOPT_URL, "http://www.php.net/");
curl_setopt($ch2, CURLOPT_HEADER, 0);

// 创建批处理cURL句柄
$mh = curl_multi_init();

// 增加2个句柄
curl_multi_add_handle($mh,$ch1);
curl_multi_add_handle($mh,$ch2);

$running=null;
// 执行批处理句柄
do {
    usleep(10000);
    curl_multi_exec($mh,$running);
} while ($running > 0);

// 关闭全部句柄
curl_multi_remove_handle($mh, $ch1);
curl_multi_remove_handle($mh, $ch2);
curl_multi_close($mh);

?>

上面两种写法的区别是执行批处理句柄这一处地方，请问哪种写法更好，还有原因是啥

在stackoverflow上找到了一个比较有用的答案，大概意思是：如果使用的curl是7.20.0之前的版本，则应该使用第一种写法；否则可以使用第二种写法。所以最保险的写法是第一种写法，第一种写法无论curl是什么版本都可以兼容。

官方文档 curl-multi-init
下面有个回复

According to [https://bugs.php.net/bug.php?id=61141:](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 curl_multi_select() always returns -1, causing the example code in the documentation to timeout. This is, apparently, not strictly a bug: according to the libcurl documentation, you should add your own sleep if curl_multi_select returns -1.

Therefore, in order to work correctly on Windows for PHP 5.3.10+, the second loop in the example code should look something like the following:

<?php
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);
}
?>