关于 php 通过 curl 的伪异步方式抓取数据，下面这种 curl 方式和普通的 curl 同步请求有什么区别？

下面是网上找到的一个类，是说可以实现 php 异步抓取数据，但是 php 一直是同步的，打印出的结果也是同步的，但是通过下面 rolling_curl 的方法，的确可以节省一定的时间，但是既然都是同步的，为什么会节约时间呢？希望各位大神能给出一些指导。 /**

cURL 批量处理工具类
@since Version 1.0
@author Justmepzy justmepzy@gmail.com
@link http://t.qq.com/JustPzy */

/**

单一的请求对象 /
class Curl_request {
public $url = '';
public $method = 'GET';
public $post_data = null;
public $headers = null;
public $options = null;
/ *
* @param string $url * @param string $method * @param string $post_data * @param string $headers * @param array $options * @return void /
public function __construct($url, $method = 'GET', $post_data = null, $headers = null, $options = null) {
$this->url = $url;
$this->method = strtoupper( $method );
$this->post_data = $post_data;
$this->headers = $headers;
$this->options = $options;
}
/* * @return void /
public function __destruct() {
unset ( $this->url, $this->method, $this->post_data, $this->headers, $this->options );
}
}
/*

包含请求列队处理 /
class Curl {
/*
- 请求 url 个数
- @var int /
  private $size = 1; /*
- 等待所有 cURL 批处理中的活动连接等待响应时间
- @var int /
  private $timeout = 5; /*
- 完成请求回调函数
- @var string /
  private $callback = null;
  /*
- cRUL 配置
- @var array /
  private $options = array (CURLOPT_SSL_VERIFYPEER => 0,CURLOPT_RETURNTRANSFER => 1,CURLOPT_CONNECTTIMEOUT => 30 );
  /*
- 请求头
- @var array /
  private $headers = array ();
  /*
- 请求列队
- @var array /
  private $requests = array ();
  /*
- 请求列队索引
- @var array /
  private $request_map = array ();
  /*
- 错误
- @var array /
  private $errors = array ();
  /*
- @access public
- @param string $callback 回调函数
- 该函数有 4 个参数($response,$info,$error,$request)
- $response url 返回的 body
- $info cURL 连接资源句柄的信息
- $error 错误
- $request 请求对象 /
  public function __construct($callback = null) {
  $this->callback = $callback;
  }
  /*
- 添加一个请求对象到列队
- @access public
- @param object $request
- @return boolean /
  public function add($request) { $this->requests [] = $request;
  return TRUE;
  }
  /*
- 创建一个请求对象并添加到列队
- @access public
- @param string $url
- @param string $method
- @param string $post_data
- @param string $headers
- @param array $options
- @return boolean /
  public function request($url, $method = 'GET', $post_data = null, $headers = null, $options = null) {
  $this->requests [] = new Curl_request ( $url, $method, $post_data, $headers, $options );
  return TRUE;
  }
  /*
- 创建 GET 请求对象
- @access public
- @param string $url
- @param string $headers
- @param array $options
- @return boolean /
  public function get($url, $headers = null, $options = null) {
  return $this->request ( $url, "GET", null, $headers, $options );
  }
  /*
- 创建一个 POST 请求对象
- @access public
- @param string $url
- @param string $post_data
- @param string $headers
- @param array $options
- @return boolean /
  public function post($url, $post_data = null, $headers = null, $options = null) {
  return $this->request ( $url, "POST", $post_data, $headers, $options );
  }
  /*
- 执行 cURL
- @access public
- @param int $size 最大连接数
- @return Ambigous <boolean, mixed>|boolean /
  public function execute($size = null) {
  if (sizeof ( $this->requests ) == 1) {
  return $this->single_curl ();
  } else { return $this->rolling_curl ( $size ); }
  }
  /*
- 单个 url 请求
- @access private
- @return mixed|boolean */
  private function single_curl() { $ch = curl_init (); $request = array_shift ( $this->requests ); $options = $this->get_options ( $request ); curl_setopt_array ( $ch, $options ); $output = curl_exec ( $ch ); $info = curl_getinfo ( $ch );
  
  // it's not neccesary to set a callback for one-off requests if ($this->callback) { $callback = $this->callback; if (is_callable ( $this->callback )) { call_user_func ( $callback, $output, $info, $request ); } } else return $output; return true; }
  /**
- 多个 url 请求
- @access private
- @param int $size 最大连接数
- @return boolean */
  private function rolling_curl($size = null) {
  if ($size)
  $this->size = $size;
  else
  $this->size = count($this->requests);
  if (sizeof ( $this->requests ) < $this->size)
  $this->size = sizeof ( $this->requests );
  if ($this->size < 2)
  $this->set_error ( 'size must be greater than 1' );
  $master = curl_multi_init ();
  //添加 cURL 连接资源句柄到 map 索引
  for($i = 0; $i < $this->size; $i ++) {
  $ch = curl_init (); $options = $this->get_options ( $this->requests [$i] ); curl_setopt_array ( $ch, $options );
  curl_multi_add_handle ( $master, $ch );
```
 $key = ( string ) $ch;  
 $this->request_map [$key] = $i;  
```
  }
  
  $active = $done = null;
  do {
  while ( ($execrun = curl_multi_exec ( $master, $active )) == CURLM_CALL_MULTI_PERFORM )
  ;
  if ($execrun != CURLM_OK)
  break;
  //有一个请求完成则回调
  while ( $done = curl_multi_info_read ( $master ) ) {
  //$done 完成的请求句柄
  $info = curl_getinfo ( $done ['handle'] );//
  $output = curl_multi_getcontent ( $done ['handle'] );//
  $error = curl_error ( $done ['handle'] );//
```
     $this->set_error ( $error );  

     //调用回调函数,如果存在的话  
     $callback = $this->callback;  
     if (is_callable ( $callback )) {  
         $key = ( string ) $done ['handle'];  
         $request = $this->requests [$this->request_map [$key]];  
         unset ( $this->request_map [$key] );
         call_user_func ( $callback, $output, $info, $error, $request );
     }  
     curl_close ( $done ['handle'] );  
     //从列队中移除已经完成的 request  
     curl_multi_remove_handle ( $master, $done ['handle'] );  
 }  
 //等待所有 cURL 批处理中的活动连接  
 if ($active)  
     curl_multi_select ( $master, $this->timeout );  
```
  } while ( $active );
  //完成关闭
  curl_multi_close ( $master );
  return true;
  }
  /**
- 获取没得请求对象的 cURL 配置
- @access private
- @param object $request
- @return array */
  private function get_options($request) {
  $options = $this->__get ( 'options' );
  if (ini_get ( 'safe_mode' ) == 'Off' || ! ini_get ( 'safe_mode' )) {
  $options [CURLOPT_FOLLOWLOCATION] = 1;
  $options [CURLOPT_MAXREDIRS] = 5;
  }
  //$headers = $this->__get ( 'headers' );
  $headers = $request->headers;
  if ($request->options) {
  $options = $request->options + $options;
  }
  
  $options [CURLOPT_URL] = $request->url;
  
  if ($request->post_data && strtolower($request->method) == 'post' ) {
  $options [CURLOPT_POST] = 1;
  $options [CURLOPT_POSTFIELDS] = $request->post_data;
  }
  
  if ($headers) {
  $options [CURLOPT_HEADER] = 0;
  $options [CURLOPT_HTTPHEADER] = $headers;
  }
  
  return $options;
  }
  /**
- 设置错误信息
- @access public
- @param string $msg /
  public function set_error($msg) {
  if (! empty ( $msg ))
  $this->errors [] = $msg;
  }
  /*
- 获取错误信息
- @access public
- @param string $open
- @param string $close
- @return string /
  public function display_errors($open = '
  ', $close = '
  ') {
  $str = '';
  foreach ( $this->errors as $val ) {
  $str .= $open . $val . $close;
  }
  return $str;
  }
  /*
- @access public
- @param string $name
- @param string $value
- @return boolean /
  public function __set($name, $value) {
  if ($name == 'options' || $name == 'headers') {
  $this->{$name} = $value + $this->{$name};
  } else {
  $this->{$name} = $value;
  }
  return TRUE;
  }
  /*
- @param string $name
- @return mixed
- @access public /
  public function __get($name) {
  return (isset ( $this->{$name} )) ? $this->{$name} : null;
  }
  /*
- @return void
- @access public /
  public function __destruct() {
  unset ( $this->size, $this->timeout, $this->callback, $this->options, $this->headers, $this->requests, $this->request_map, $this->errors );
  }
  }
  // END Curl Class
  / End of file curl.class.php */