Rolling cURL:PHP并发最佳实践

文章目录

1. 1. 经典cURL并发机制及其存在的问题

前言：在实际项目或者自己编写小工具(比如新闻聚合,商品价格监控,比价)的过程中, 通常需要从第3方网站或者API接口获取数据, 在需要处理1个URL队列时, 为了提高性能, 可以采用cURL提供的curl_multi_*族函数实现简单的并发.

本文将探讨两种具体的实现方法, 并对不同的方法做简单的性能对比.

经典cURL并发机制及其存在的问题

经典的cURL实现机制在网上很容易找到, 比如参考PHP在线手册在线手册，不过这里我附上我们BI项目中使用的多并发方式:

public static function multi_curl_new($requests) {
    $mh = curl_multi_init();
    $chs = array();
    foreach ($requests as $key => $req) {
        $timeout = empty($req['timeout']) ? 20 : $req['timeout'];
        $ch = curl_init($req['url']);
        curl_setopt($ch, CURLOPT_TIMEOUT, $timeout);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
        if(defined('CURLOPT_IPRESOLVE') && defined('CURL_IPRESOLVE_V4')) {
            curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
        }
        if(empty($req['not_need_proxy'])) {
            MY_Pull::set_curl_proxy($req['big_app_id'], $ch);
        }
        curl_multi_add_handle($mh, $ch);
        $chs[$key] = $ch;
    }

    $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) {
            do {
                $mrc = curl_multi_exec($mh, $active);
            } while($mrc == CURLM_CALL_MULTI_PERFORM);
        }
        usleep(100);
    }

    $rets = array();
    foreach($chs as $key => $ch) {
        $rets[$key] = curl_multi_getcontent($ch);
        curl_multi_remove_handle($mh, $ch);
        curl_close($ch);
    }
    curl_multi_close($mh);

    return $rets;
}

首先将所有的URL压入并发队列, 然后执行并发过程, 等待所有请求接收完之后进行数据的解析等后续处理. 在实际的处理过程中, 受网络传输的影响, 部分URL的内容会优先于其他URL返回, 但是经典cURL并发必须等待最慢的那个URL返回之后才开始处理, 等待也就意味着CPU的空闲和浪费. 如果URL队列很短, 这种空闲和浪费还处在可接受的范围, 但如果队列很长, 这种等待和浪费将变得不可接受.

##改进的Rolling cURL并发方式

仔细分析不难发现经典cURL并发还存在优化的空间, 优化的方式时当某个URL请求完毕之后尽可能快的去处理它, 边处理边等待其他的URL返回, 而不是等待那个最慢的接口返回之后才开始处理等工作, 从而避免CPU的空闲和浪费. 闲话不多说, 下面贴上具体的实现:

function rolling_curl($urls, $delay) {
    $queue = curl_multi_init();
    $map = array();

    foreach ($urls as $url) {
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_TIMEOUT, 1);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_HEADER, 0);
        curl_setopt($ch, CURLOPT_NOSIGNAL, true);

        curl_multi_add_handle($queue, $ch);
        $map[(string) $ch] = $url;
    }

    $responses = array();
    do {
        while (($code = curl_multi_exec($queue, $active)) == CURLM_CALL_MULTI_PERFORM) ;

        if ($code != CURLM_OK) { break; }

        // a request was just completed -- find out which one
        while ($done = curl_multi_info_read($queue)) {

            // get the info and content returned on the request
            $info = curl_getinfo($done['handle']);
            $error = curl_error($done['handle']);
            $results = callback(curl_multi_getcontent($done['handle']), $delay);
            $responses[$map[(string) $done['handle']]] = compact('info', 'error', 'results');

            // remove the curl handle that just completed
            curl_multi_remove_handle($queue, $done['handle']);
            curl_close($done['handle']);
        }

        // Block for data in / output; error handling is done by curl_multi_exec
        if ($active > 0) {
            curl_multi_select($queue, 0.5);
        }

    } while ($active);

    curl_multi_close($queue);
    return $responses;
}

引自文章 http://www.searchtb.com/2012/06/rolling-curl-best-practices.html