curl/docs/examples/10-at-a-time.c

/*****************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 *
 * Example application source code using the multi interface to download many
 * files, but with a capped maximum amount of simultaneous transfers.
 *
 * Written by Michael Wallner
 */

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#ifndef WIN32
#  include <unistd.h>
#endif
#include <curl/multi.h>

static const char *urls[] = {
  "http://www.microsoft.com",
  "http://www.opensource.org",
  "http://www.google.com",
  "http://www.yahoo.com",
  "http://www.ibm.com",
  "http://www.mysql.com",
  "http://www.oracle.com",
  "http://www.ripe.net",
  "http://www.iana.org",
  "http://www.amazon.com",
  "http://www.netcraft.com",
  "http://www.heise.de",
  "http://www.chip.de",
  "http://www.ca.com",
  "http://www.cnet.com",
  "http://www.news.com",
  "http://www.cnn.com",
  "http://www.wikipedia.org",
  "http://www.dell.com",
  "http://www.hp.com",
  "http://www.cert.org",
  "http://www.mit.edu",
  "http://www.nist.gov",
  "http://www.ebay.com",
  "http://www.playstation.com",
  "http://www.uefa.com",
  "http://www.ieee.org",
  "http://www.apple.com",
  "http://www.sony.com",
  "http://www.symantec.com",
  "http://www.zdnet.com",
  "http://www.fujitsu.com",
  "http://www.supermicro.com",
  "http://www.hotmail.com",
  "http://www.ecma.com",
  "http://www.bbc.co.uk",
  "http://news.google.com",
  "http://www.foxnews.com",
  "http://www.msn.com",
  "http://www.wired.com",
  "http://www.sky.com",
  "http://www.usatoday.com",
  "http://www.cbs.com",
  "http://www.nbc.com",
  "http://slashdot.org",
  "http://www.bloglines.com",
  "http://www.techweb.com",
  "http://www.newslink.org",
  "http://www.un.org",
};

#define MAX 10 /* number of simultaneous transfers */
#define CNT sizeof(urls)/sizeof(char*) /* total number of transfers to do */

static size_t cb(char *d, size_t n, size_t l, void *p)
{
  /* take care of the data here, ignored in this example */
  (void)d;
  (void)p;
  return n*l;
}

static void init(CURLM *cm, int i)
{
  CURL *eh = curl_easy_init();

  curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, cb);
  curl_easy_setopt(eh, CURLOPT_HEADER, 0L);
  curl_easy_setopt(eh, CURLOPT_URL, urls[i]);
  curl_easy_setopt(eh, CURLOPT_PRIVATE, urls[i]);
  curl_easy_setopt(eh, CURLOPT_VERBOSE, 0L);

  curl_multi_add_handle(cm, eh);
}

int main(void)
{
  CURLM *cm;
  CURLMsg *msg;
  long L;
  unsigned int C=0;
  int M, Q, U = -1;
  fd_set R, W, E;
  struct timeval T;

  curl_global_init(CURL_GLOBAL_ALL);

  cm = curl_multi_init();

  /* we can optionally limit the total amount of connections this multi handle
     uses */
  curl_multi_setopt(cm, CURLMOPT_MAXCONNECTS, (long)MAX);

  for (C = 0; C < MAX; ++C) {
    init(cm, C);
  }

  while (U) {
    curl_multi_perform(cm, &U);

    if (U) {
      FD_ZERO(&R);
      FD_ZERO(&W);
      FD_ZERO(&E);

      if (curl_multi_fdset(cm, &R, &W, &E, &M)) {
        fprintf(stderr, "E: curl_multi_fdset\n");
        return EXIT_FAILURE;
      }

      if (curl_multi_timeout(cm, &L)) {
        fprintf(stderr, "E: curl_multi_timeout\n");
        return EXIT_FAILURE;
      }
      if (L == -1)
        L = 100;

      if (M == -1) {
#ifdef WIN32
        Sleep(L);
#else
        sleep(L / 1000);
#endif
      } else {
        T.tv_sec = L/1000;
        T.tv_usec = (L%1000)*1000;

        if (0 > select(M+1, &R, &W, &E, &T)) {
          fprintf(stderr, "E: select(%i,,,,%li): %i: %s\n",
              M+1, L, errno, strerror(errno));
          return EXIT_FAILURE;
        }
      }
    }

    while ((msg = curl_multi_info_read(cm, &Q))) {
      if (msg->msg == CURLMSG_DONE) {
        char *url;
        CURL *e = msg->easy_handle;
        curl_easy_getinfo(msg->easy_handle, CURLINFO_PRIVATE, &url);
        fprintf(stderr, "R: %d - %s <%s>\n",
                msg->data.result, curl_easy_strerror(msg->data.result), url);
        curl_multi_remove_handle(cm, e);
        curl_easy_cleanup(e);
      }
      else {
        fprintf(stderr, "E: CURLMsg (%d)\n", msg->msg);
      }
      if (C < CNT) {
        init(cm, C++);
        U++; /* just to prevent it from remaining at 0 if there are more
                URLs to get */
      }
    }
  }

  curl_multi_cleanup(cm);
  curl_global_cleanup();

  return EXIT_SUCCESS;
}