Rolling cURL: PHP并發最佳實踐
在實際項目或者自己編寫小工具(比如新聞聚合,商品價格監控,比價)的過程中, 通常需要從第3方網站或者API接口獲取數據, 在需要處理1個URL隊列時, 為了提高性能, 可以采用cURL提供的curl_multi_*族函數實現簡單的并發.
本文將探討兩種具體的實現方法, 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實現機制在網上很容易找到, 比如參考PHP在線手冊的如下實現方式:
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 $responses;
}
首先將所有的URL壓入并發隊列, 然后執行并發過程, 等待所有請求接收完之后進行數據的解析等后續處理. 在實際的處理過程中, 受網絡傳輸的影響, 部分URL的內容會優先于其他URL返回, 但是經典cURL并發必須等待最慢的那個URL返回之后才開始處理, 等待也就意味著CPU的空閑和浪費. 如果URL隊列很短, 這種空閑和浪費還處在可接受的范圍, 但如果隊列很長, 這種等待和浪費將變得不可接受.
2. 改進的Rolling cURL并發方式
仔細分析不難發現經典cURL并發還存在優化的空間, 優化的方式時當某個URL請求完畢之后盡可能快的去處理它, 邊處理邊等待其他的URL返回, 而不是等待那個最慢的接口返回之后才開始處理等工作, 從而避免CPU的空閑和浪費. 閑話不多說, 下面貼上具體的實現:
function rolling_curl($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 $responses;
}
3. 兩種并發實現的性能對比
改進前后的性能對比試驗在LINUX主機上進行, 測試時使用的并發隊列如下:
- http://item.taobao.com/item.htm?id=14392877692
- http://item.taobao.com/item.htm?id=16231676302
- http://item.taobao.com/item.htm?id=17037160462
- http://item.taobao.com/item.htm?id=5522416710
- http://item.taobao.com/item.htm?id=16551116403
- http://item.taobao.com/item.htm?id=14088310973
簡要說明下實驗設計的原則和性能測試結果的格式: 為保證結果的可靠, 每組實驗重復20次, 在單次實驗中, 給定相同的接口URL集合, 分別測量Classic(指經典的并發機制)和Rolling(指改進后的并發機制)兩種并發機制的耗時(秒為單位), 耗時短者勝出(Winner), 并計算節省的時間(Excellence, 秒為單位)以及性能提升比例(Excel. %). 為了盡量貼近真實的請求而又保持實驗的簡單, 在對返回結果的處理上只是做了簡單的正則表達式匹配, 而沒有進行其他復雜的操作. 另外, 為了確定結果處理回調對性能對比測試結果的影響, 可以使用usleep模擬現實中比較負責的數據處理邏輯(如提取, 分詞, 寫入文件或數據庫等).
性能測試中用到的回調函數為:
function callback($data, $delay) {
preg_match_all('/<h3>(.+)<\/h3>/iU', $data, $matches);
usleep($delay);
return compact('data', 'matches');
}
數據處理回調無延遲時: 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
數據處理回調延遲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隊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, 可以控制并發隊列的最大長度, 比如20, 每當1個URL返回并處理完畢之后立即加入1個尚未請求的URL到隊列中, 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. 詳細的實現請參考: http://code.google.com/p/rolling-curl/
5. 參考資料和延伸閱讀
- Client URL Library http://www.php.net/manual/en/book.curl.php
- Parallel CURL Requests with PHP http://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 Performance http://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
本文由用戶 openkk 自行上傳分享，僅供網友學習交流。所有權歸原作者，若您的權利被侵害，請聯系管理員。
轉載本站原創文章，請注明出處，并保留原始鏈接、圖片水印。
本站是一個以用戶分享為主的開源技術平臺，歡迎各類分享！