求指点：关于LINUX C LIBCURL问题

[pygmalion]

日前做一个抓去网页的C程序,开始的时候参照了一下curl官网一段代码：

/* This is an example application source code using the multi interface. */ 
 
#include <stdio.h>
#include <string.h>
 
/* somewhat unix-specific */ 
#include <sys/time.h>
#include <unistd.h>
 
/* curl stuff */ 
#include <curl/curl.h>
 
/*
 * Download a HTTP file and upload an FTP file simultaneously.
 */ 
 
#define HANDLECOUNT 2    
#define HTTP_HANDLE 0    
#define FTP_HANDLE 1     
 
int main(void)
{
  CURL *handles[HANDLECOUNT];
  CURLM *multi_handle;
 
  int still_running; /* keep number of running handles */ 
  int i;
 
  CURLMsg *msg; /* for picking up messages with the transfer status */ 
  int msgs_left; /* how many messages are left */ 
 
  /* Allocate one CURL handle per transfer */ 
  for (i=0; i<HANDLECOUNT; i++)
      handles[i] = curl_easy_init();
 
  /* set the options (I left out a few, you'll get the point anyway) */ 
  curl_easy_setopt(handles[HTTP_HANDLE], CURLOPT_URL, "http://example.com");
 
  curl_easy_setopt(handles[FTP_HANDLE], CURLOPT_URL, "ftp://example.com");
  curl_easy_setopt(handles[FTP_HANDLE], CURLOPT_UPLOAD, 1L);
 
  /* init a multi stack */ 
  multi_handle = curl_multi_init();
 
  /* add the individual transfers */ 
  for (i=0; i<HANDLECOUNT; i++)
      curl_multi_add_handle(multi_handle, handles[i]);
 
  /* we start some action by calling perform right away */ 
  curl_multi_perform(multi_handle, &still_running);
 
  do {
    struct timeval timeout;
    int rc; /* select() return code */ 
 
    fd_set fdread;
    fd_set fdwrite;
    fd_set fdexcep;
    int maxfd = -1;
 
    long curl_timeo = -1;
 
    FD_ZERO(&fdread);
    FD_ZERO(&fdwrite);
    FD_ZERO(&fdexcep);
 
    /* set a suitable timeout to play around with */ 
    timeout.tv_sec = 1;
    timeout.tv_usec = 0;
 
    curl_multi_timeout(multi_handle, &curl_timeo);
    if(curl_timeo >= 0) {
      timeout.tv_sec = curl_timeo / 1000;
      if(timeout.tv_sec > 1)
        timeout.tv_sec = 1;
      else
        timeout.tv_usec = (curl_timeo % 1000) * 1000;
    }
 
    /* get file descriptors from the transfers */ 
    curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
    /* In a real-world program you OF COURSE check the return code of the
       function calls.  On success, the value of maxfd is guaranteed to be
       greater or equal than -1.  We call select(maxfd + 1, ...), specially in
       case of (maxfd == -1), we call select(0, ...), which is basically equal
       to sleep. */ 
 
    rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
    switch(rc) {
    case -1:
      /* select error */ 
      break;
    case 0: /* timeout */ 
    default: /* action */ 
      curl_multi_perform(multi_handle, &still_running);
      break;
    }
  } while(still_running);
 
  /* See how the transfers went */ 
  while ((msg = curl_multi_info_read(multi_handle, &msgs_left))) {
    if (msg->msg == CURLMSG_DONE) {
      int idx, found = 0;
 
      /* Find out which handle this message is about */ 
      for (idx=0; idx<HANDLECOUNT; idx++) {
        found = (msg->easy_handle == handles[idx]);
        if(found)
          break;
      }
 
      switch (idx) {
      case HTTP_HANDLE:
        printf("HTTP transfer completed with status %d\n", msg->data.result);
        break;
      case FTP_HANDLE:
        printf("FTP transfer completed with status %d\n", msg->data.result);
        break;
      }
    }
  }
 
  curl_multi_cleanup(multi_handle);
 
  /* Free the CURL handles */ 
  for (i=0; i<HANDLECOUNT; i++)
      curl_easy_cleanup(handles[i]);
 
  return 0;
}

为了提高效率，我使用了多线程，在每个线程里面进行抓取，最后发现运行时间并没有大幅降低。很疑惑，请高手解答一下。