Rolling cURL: PHP并发最佳实践

openkk 12年前

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.

1. 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在线手册的如下实现方式: 

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.

2. 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;  }

3. 两种并发实现的性能对比

改进前后的性能对比试验在LINUX主机上进行, 测试时使用的并发队列如下:

简要说明下实验设计的原则和性能测试结果的格式: 为保证结果的可靠, 每组实验重复20次, 在单次实验中, 给定相同的接口URL集合, 分别测量Classic(指经典的并发机制)和Rolling(指改进后的并发机制)两种并发机制的耗时(秒为单位), 耗时短者胜出(Winner), 并计算节省的时间(Excellence, 秒为单位)以及性能提升比例(Excel. %). 为了尽量贴近真实的请求而又保持实验的简单, 在对返回结果的处理上只是做了简单的正则表达式匹配, 而没有进行其他复杂的操作. 另外, 为了确定结果处理回调对性能对比测试结果的影响, 可以使用usleep模拟现实中比较负责的数据处理逻辑(如提取, 分词, 写入文件或数据库等).

性能测试中用到的回调函数为:

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

数据处理回调无延迟时: Rolling Curl略优, 但性能提升效果不明显.

------------------------------------------------------------------------------------------------  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

数据处理回调延迟5毫秒: Rolling Curl完胜, 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

通过上面的性能对比, 在处理URL队列并发的应用场景中Rolling cURL应该是更加的选择, 并发量非常大(1000+)时, 可以控制并发队列的最大长度, 比如20, 每当1个URL返回并处理完毕之后立即加入1个尚未请求的URL到队列中, 这样写出来的代码会更加健壮, 不至于并发数太大而卡死或崩溃. 详细的实现请参考: http://code.google.com/p/rolling-curl/

5. 参考资料和延伸阅读

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