text: /***************************************************************************
   *                                  _   _ ____  _
   *  Project                     ___| | | |  _ \| |
   *                             / __| | | | |_) | |
   *                            | (__| |_| |  _ <| |___
   *                             \___|\___/|_| \_\_____|
   *
   * Copyright (C) 1998 - 2017, 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.haxx.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>
   * Multi-threaded transfers sharing a single connection pool
   * </DESC>
   *
   * This example fires up NUM_THREADS threads and in each single thread, it
   * downloads the same fixed URL a URL_ITERATIONS number of times. The received
   * data is just thrown away. It sets up a single shared object that holds the
   * connection cache and all easy handles in all threads share that same cache.
   *
   * This example uses pthreads for threads and mutexes, but should be easy to
   * modify to use different thread/mutex system should you want to.
   *
   */
  
  #include <stdio.h>
  #include <pthread.h>
  #include <curl/curl.h>
  
  /*
    URL to fetch. If you select HTTPS, you need to use a TLS backend with mutex
    locks taken care of (OpenSSL 1.1.x, NSS, etc) or add SSL mutex callbacks!
  */
  #define URL "http://localhost/4KB"
  
  /* number of threads to fire up in parallel */
  #define NUM_THREADS 67
  
  /* how many times each URL is transferred per thread */
  #define URL_ITERATIONS 11235
  
  static pthread_mutex_t connlock;
  
  static size_t write_db(void *ptr, size_t size, size_t nmemb, void *data)
  {
    /* not interested in the downloaded bytes, return the size */
    (void)ptr;  /* unused */
    (void)data; /* unused */
    return (size_t)(size * nmemb);
  }
  
  static void lock_cb(CURL *handle, curl_lock_data data,
                      curl_lock_access access, void *userptr)
  {
    (void)access; /* unused */
    (void)userptr; /* unused */
    (void)handle; /* unused */
    (void)data; /* unused */
    pthread_mutex_lock(&connlock);
  }
  
  static void unlock_cb(CURL *handle, curl_lock_data data,
                        void *userptr)
  {
    (void)userptr; /* unused */
    (void)handle;  /* unused */
    (void)data;    /* unused */
    pthread_mutex_unlock(&connlock);
  }
  
  static void init_locks(void)
  {
    pthread_mutex_init(&connlock, NULL);
  }
  
  static void kill_locks(void)
  {
    pthread_mutex_destroy(&connlock);
  }
  
  struct initurl {
    const char *url;
    CURLSH *share;
    int threadno;
  };
  
  static void *run_thread(void *ptr)
  {
    struct initurl *u = (struct initurl *)ptr;
    int i;
  
    for(i = 0; i < URL_ITERATIONS; i++) {
      CURL *curl = curl_easy_init();
      curl_easy_setopt(curl, CURLOPT_URL, u->url);
      curl_easy_setopt(curl, CURLOPT_VERBOSE, 0L);
      curl_easy_setopt(curl, CURLOPT_SHARE, u->share);
      curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_db);
      curl_easy_perform(curl); /* ignores error */
      curl_easy_cleanup(curl);
      fprintf(stderr, "Thread %d transfer %d\n", u->threadno, i);
    }
  
    return NULL;
  }
  
  int main(void)
  {
    pthread_t tid[NUM_THREADS];
    int i;
    int error;
    CURLSH *share;
    struct initurl url[NUM_THREADS];
  
    /* Must initialize libcurl before any threads are started */
    curl_global_init(CURL_GLOBAL_ALL);
  
    share = curl_share_init();
    curl_share_setopt(share, CURLSHOPT_LOCKFUNC, lock_cb);
    curl_share_setopt(share, CURLSHOPT_UNLOCKFUNC, unlock_cb);
    curl_share_setopt(share, CURLSHOPT_SHARE, CURL_LOCK_DATA_CONNECT);
  
    init_locks();
  
    for(i = 0; i< NUM_THREADS; i++) {
      url[i].url = URL;
      url[i].share = share;
      url[i].threadno = i;
      error = pthread_create(&tid[i], NULL, run_thread, &url[i]);
      if(0 != error)
        fprintf(stderr, "Couldn't run thread number %d, errno %d\n", i, error);
      else
        fprintf(stderr, "Thread %d, gets %s\n", i, URL);
    }
  
    /* now wait for all threads to terminate */
    for(i = 0; i< NUM_THREADS; i++) {
      error = pthread_join(tid[i], NULL);
      fprintf(stderr, "Thread %d terminated\n", i);
    }
  
    kill_locks();
  
    curl_share_cleanup(share);
    curl_global_cleanup();
    return 0;
  }
  