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:
代码如下:
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 $responses;
}
首先将所有的URL压入并发队列, 然后执行并发过程, 等待所有请求接收完之后进行数据的解析等后续处理. 在实际的处理过程中, 受网络传输的影响, 部分URL的内容会优先于其他URL返回, 但是经典cURL并发必须等待最慢的那个URL返回之后才开始处理, 等待也就意味着CPU的空闲和浪费. 如果URL队列很短, 这种空闲和浪费还处在可接受的范围, 但如果队列很长, 这种等待和浪费将变得不可接受.
2. 改进的Rolling cURL并发方式
仔细分析不难发现经典cURL并发还存在优化的空间, 优化的方式时当某个URL请求完毕之后尽可能快的去处理它, 边处理边等待其他的URL返回, 而不是等待那个最慢的接口返回之后才开始处理等工作, 从而避免CPU的空闲和浪费. 闲话不多说, 下面贴上具体的实现:
代码如下:
function rolling_curl($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)) {
