Rolling cURL: PHP并發最佳實踐【轉】-有解無憂

在實際專案或者自己撰寫小工具(比如新聞聚合,商品價格監控,比價)的程序中, 通常需要從第3方網站或者API介面獲取資料, 在需要處理1個URL佇列時, 為了提高性能, 可以采用cURL提供的curl_multi_*族函式實作簡單的并發.

本文將探討兩種具體的實作方法, 并對不同的方法做簡單的性能對比.

1. 經典cURL并發機制及其存在的問題

經典的cURL實作機制在網上很容易找到, 比如參考PHP在線手冊的如下實作方式:

function classic_curl($urls, $delay) {
    $queue = curl_multi_init();
    $map = array();
 
    foreach ($urls as $url) {
        // create cURL resources
        $ch = curl_init();
 
        // set URL and other appropriate options
        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);
 
        // add handle
        curl_multi_add_handle($queue, $ch);
        $map[$url] = $ch;
    }
 
    $active = null;
 
    // execute the handles
    do {
        $mrc = curl_multi_exec($queue, $active);
    } while ($mrc == CURLM_CALL_MULTI_PERFORM);
 
    while ($active > 0 && $mrc == CURLM_OK) {
        if (curl_multi_select($queue, 0.5) != -1) {
            do {
                $mrc = curl_multi_exec($queue, $active);
            } while ($mrc == CURLM_CALL_MULTI_PERFORM);
        }
    }
 
    $responses = array();
    foreach ($map as $url=>$ch) {
        $responses[$url] = callback(curl_multi_getcontent($ch), $delay);
        curl_multi_remove_handle($queue, $ch);
        curl_close($ch);
    }
 
    curl_multi_close($queue);
    return $responses;
}

首先將所有的URL壓入并發佇列, 然后執行并發程序, 等待所有請求接收完之后進行資料的決議等后續處理. 在實際的處理程序中, 受網路傳輸的影響, 部分URL的內容會優先于其他URL回傳, 但是經典cURL并發必須等待最慢的那個URL回傳之后才開始處理, 等待也就意味著CPU的空閑和浪費. 如果URL佇列很短, 這種空閑和浪費還處在可接受的范圍, 但如果佇列很長, 這種等待和浪費將變得不可接受.

2. 改進的Rolling cURL并發方式

仔細分析不難發現經典cURL并發還存在優化的空間, 優化的方式時當某個URL請求完畢之后盡可能快的去處理它, 邊處理邊等待其他的URL回傳, 而不是等待那個最慢的介面回傳之后才開始處理等作業, 從而避免CPU的空閑和浪費. 閑話不多說, 下面貼上具體的實作:

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;
}

3. 兩種并發實作的性能對比

改進前后的性能對比試驗在LINUX主機上進行, 測驗時使用的并發佇列如下:

http://item.taobao.com/item.htm?id=14392877692
http://item.taobao.com/item.htm?id=16231676302
http://item.taobao.com/item.htm?id=17037160462
http://item.taobao.com/item.htm?id=5522416710
http://item.taobao.com/item.htm?id=16551116403
http://item.taobao.com/item.htm?id=14088310973

簡要說明下實驗設計的原則和性能測驗結果的格式: 為保證結果的可靠, 每組實驗重復20次, 在單次實驗中, 給定相同的介面URL集合, 分別測量Classic(指經典的并發機制)和Rolling(指改進后的并發機制)兩種并發機制的耗時(秒為單位), 耗時短者勝出(Winner), 并計算節省的時間(Excellence, 秒為單位)以及性能提升比例(Excel. %). 為了盡量貼近真實的請求而又保持實驗的簡單, 在對回傳結果的處理上只是做了簡單的正則運算式匹配, 而沒有進行其他復雜的操作. 另外, 為了確定結果處理回呼對性能對比測驗結果的影響, 可以使用usleep模擬現實中比較負責的資料處理邏輯(如提取, 分詞, 寫入檔案或資料庫等).

性能測驗中用到的回呼函式為:

function callback($data, $delay) {
    preg_match_all('/<h3>(.+)</h3>/iU', $data, $matches);
    usleep($delay);
    return compact('data', 'matches');
}

資料處理回呼無延遲時: Rolling Curl略優, 但性能提升效果不明顯.

------------------------------------------------------------------------------------------------
Delay: 0 micro seconds, equals to 0 milli seconds
------------------------------------------------------------------------------------------------
Counter         Classic         Rolling         Winner          Excellence      Excel. %
------------------------------------------------------------------------------------------------
1               0.1193          0.0390          Rolling         0.0803          67.31%
2               0.0556          0.0477          Rolling         0.0079          14.21%
3               0.0461          0.0588          Classic         -0.0127         -21.6%
4               0.0464          0.0385          Rolling         0.0079          17.03%
5               0.0534          0.0448          Rolling         0.0086          16.1%
6               0.0540          0.0714          Classic         -0.0174         -24.37%
7               0.0386          0.0416          Classic         -0.0030         -7.21%
8               0.0357          0.0398          Classic         -0.0041         -10.3%
9               0.0437          0.0442          Classic         -0.0005         -1.13%
10              0.0319          0.0348          Classic         -0.0029         -8.33%
11              0.0529          0.0430          Rolling         0.0099          18.71%
12              0.0503          0.0581          Classic         -0.0078         -13.43%
13              0.0344          0.0225          Rolling         0.0119          34.59%
14              0.0397          0.0643          Classic         -0.0246         -38.26%
15              0.0368          0.0489          Classic         -0.0121         -24.74%
16              0.0502          0.0394          Rolling         0.0108          21.51%
17              0.0592          0.0383          Rolling         0.0209          35.3%
18              0.0302          0.0285          Rolling         0.0017          5.63%
19              0.0248          0.0553          Classic         -0.0305         -55.15%
20              0.0137          0.0131          Rolling         0.0006          4.38%
------------------------------------------------------------------------------------------------
Average         0.0458          0.0436          Rolling         0.0022          4.8%
------------------------------------------------------------------------------------------------
Summary: Classic wins 10 times, while Rolling wins 10 times

資料處理回呼延遲5毫秒: Rolling Curl完勝, 性能提升40%左右.

------------------------------------------------------------------------------------------------
Delay: 5000 micro seconds, equals to 5 milli seconds
------------------------------------------------------------------------------------------------
Counter         Classic         Rolling         Winner          Excellence      Excel. %
------------------------------------------------------------------------------------------------
1               0.0658          0.0352          Rolling         0.0306          46.5%
2               0.0728          0.0367          Rolling         0.0361          49.59%
3               0.0732          0.0387          Rolling         0.0345          47.13%
4               0.0783          0.0347          Rolling         0.0436          55.68%
5               0.0658          0.0286          Rolling         0.0372          56.53%
6               0.0687          0.0362          Rolling         0.0325          47.31%
7               0.0787          0.0337          Rolling         0.0450          57.18%
8               0.0676          0.0391          Rolling         0.0285          42.16%
9               0.0668          0.0351          Rolling         0.0317          47.46%
10              0.0603          0.0317          Rolling         0.0286          47.43%
11              0.0714          0.0350          Rolling         0.0364          50.98%
12              0.0627          0.0215          Rolling         0.0412          65.71%
13              0.0617          0.0401          Rolling         0.0216          35.01%
14              0.0721          0.0226          Rolling         0.0495          68.65%
15              0.0701          0.0428          Rolling         0.0273          38.94%
16              0.0674          0.0352          Rolling         0.0322          47.77%
17              0.0452          0.0425          Rolling         0.0027          5.97%
18              0.0596          0.0366          Rolling         0.0230          38.59%
19              0.0679          0.0480          Rolling         0.0199          29.31%
20              0.0657          0.0338          Rolling         0.0319          48.55%
------------------------------------------------------------------------------------------------
Average         0.0671          0.0354          Rolling         0.0317          47.24%
------------------------------------------------------------------------------------------------
Summary: Classic wins 0 times, while Rolling wins 20 times

通過上面的性能對比, 在處理URL佇列并發的應用場景中Rolling cURL應該是更加的選擇, 并發量非常大(1000+)時, 可以控制并發佇列的最大長度, 比如20, 每當1個URL回傳并處理完畢之后立即加入1個尚未請求的URL到佇列中, 這樣寫出來的代碼會更加健壯, 不至于并發數太大而卡死或崩潰. 詳細的實作請參考:http://code.google.com/p/rolling-curl/

5. 參考資料和延伸閱讀

Client URL Libraryhttp://www.php.net/manual/en/book.curl.php
Parallel CURL Requests with PHPhttp://blog.rob.cx/multi-curl
A more efficient multi-curl library for PHP (non-blocking)http://code.google.com/p/rolling-curl/
PHP: Parallel cURL Performancehttp://stackoverflow.com/questions/10485199/php-parallel-curl-performance-rollingcurl-vs-parallelcurl

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

文章轉自：https://www.oschina.net/question/54100_58279

轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/24464.html

標籤：PHP

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