text: /***************************************************************************
   *                                  _   _ ____  _
   *  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>
   * Show the required mutex callback setups for GnuTLS and OpenSSL when using
   * libcurl multi-threaded.
   * </DESC>
   */
  /* A multi-threaded example that uses pthreads and fetches 4 remote files at
   * once over HTTPS. The lock callbacks and stuff assume OpenSSL <1.1 or GnuTLS
   * (libgcrypt) so far.
   *
   * OpenSSL docs for this:
   *   https://www.openssl.org/docs/man1.0.2/man3/CRYPTO_num_locks.html
   * gcrypt docs for this:
   *   https://gnupg.org/documentation/manuals/gcrypt/Multi_002dThreading.html
   */
  
  #define USE_OPENSSL /* or USE_GNUTLS accordingly */
  
  #include <stdio.h>
  #include <pthread.h>
  #include <curl/curl.h>
  
  #define NUMT 4
  
  /* we have this global to let the callback get easy access to it */
  static pthread_mutex_t *lockarray;
  
  #ifdef USE_OPENSSL
  #include <openssl/crypto.h>
  static void lock_callback(int mode, int type, char *file, int line)
  {
    (void)file;
    (void)line;
    if(mode & CRYPTO_LOCK) {
      pthread_mutex_lock(&(lockarray[type]));
    }
    else {
      pthread_mutex_unlock(&(lockarray[type]));
    }
  }
  
  static unsigned long thread_id(void)
  {
    unsigned long ret;
  
    ret = (unsigned long)pthread_self();
    return ret;
  }
  
  static void init_locks(void)
  {
    int i;
  
    lockarray = (pthread_mutex_t *)OPENSSL_malloc(CRYPTO_num_locks() *
                                                  sizeof(pthread_mutex_t));
    for(i = 0; i<CRYPTO_num_locks(); i++) {
      pthread_mutex_init(&(lockarray[i]), NULL);
    }
  
    CRYPTO_set_id_callback((unsigned long (*)())thread_id);
    CRYPTO_set_locking_callback((void (*)())lock_callback);
  }
  
  static void kill_locks(void)
  {
    int i;
  
    CRYPTO_set_locking_callback(NULL);
    for(i = 0; i<CRYPTO_num_locks(); i++)
      pthread_mutex_destroy(&(lockarray[i]));
  
    OPENSSL_free(lockarray);
  }
  #endif
  
  #ifdef USE_GNUTLS
  #include <gcrypt.h>
  #include <errno.h>
  
  GCRY_THREAD_OPTION_PTHREAD_IMPL;
  
  void init_locks(void)
  {
    gcry_control(GCRYCTL_SET_THREAD_CBS);
  }
  
  #define kill_locks()
  #endif
  
  /* List of URLs to fetch.*/
  const char * const urls[]= {
    "https://www.example.com/",
    "https://www2.example.com/",
    "https://www3.example.com/",
    "https://www4.example.com/",
  };
  
  static void *pull_one_url(void *url)
  {
    CURL *curl;
  
    curl = curl_easy_init();
    curl_easy_setopt(curl, CURLOPT_URL, url);
    /* this example doesn't verify the server's certificate, which means we
       might be downloading stuff from an impostor */
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
    curl_easy_perform(curl); /* ignores error */
    curl_easy_cleanup(curl);
  
    return NULL;
  }
  
  int main(int argc, char **argv)
  {
    pthread_t tid[NUMT];
    int i;
    (void)argc; /* we don't use any arguments in this example */
    (void)argv;
  
    /* Must initialize libcurl before any threads are started */
    curl_global_init(CURL_GLOBAL_ALL);
  
    init_locks();
  
    for(i = 0; i< NUMT; i++) {
      int error = pthread_create(&tid[i],
                                 NULL, /* default attributes please */
                                 pull_one_url,
                                 (void *)urls[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, urls[i]);
    }
  
    /* now wait for all threads to terminate */
    for(i = 0; i< NUMT; i++) {
      pthread_join(tid[i], NULL);
      fprintf(stderr, "Thread %d terminated\n", i);
    }
  
    kill_locks();
  
    return 0;
  }
  