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

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/
/* <DESC>
 * Download many files in parallel, in the same thread.
 * </DESC>
 */

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

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

#define MAX_PARALLEL 10 /* number of simultaneous transfers */
#define NUM_URLS sizeof(urls)/sizeof(char *)

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

static void add_transfer(CURLM *cm, int i)
{
  CURL *eh = curl_easy_init();
  curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, write_cb);
  curl_easy_setopt(eh, CURLOPT_URL, urls[i]);
  curl_easy_setopt(eh, CURLOPT_PRIVATE, urls[i]);
  curl_multi_add_handle(cm, eh);
}

int main(void)
{
  CURLM *cm;
  CURLMsg *msg;
  unsigned int transfers = 0;
  int msgs_left = -1;
  int still_alive = 1;

  curl_global_init(CURL_GLOBAL_ALL);
  cm = curl_multi_init();

  /* Limit the amount of simultaneous connections curl should allow: */
  curl_multi_setopt(cm, CURLMOPT_MAXCONNECTS, (long)MAX_PARALLEL);

  for(transfers = 0; transfers < MAX_PARALLEL; transfers++)
    add_transfer(cm, transfers);

  do {
    curl_multi_perform(cm, &still_alive);

    while((msg = curl_multi_info_read(cm, &msgs_left))) {
      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(transfers < NUM_URLS)
        add_transfer(cm, transfers++);
    }
    if(still_alive)
      curl_multi_wait(cm, NULL, 0, 1000, NULL);

  } while(still_alive || (transfers < NUM_URLS));

  curl_multi_cleanup(cm);
  curl_global_cleanup();

  return EXIT_SUCCESS;
}