Rolling cURL: PHP并发最佳实践

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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

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