examples/threaded-ssl: remove locking callback code

- Remove the locking callback code that demonstrates how to meet
  requirements of threading libraries (mainly OpenSSL).

Locking callback code has not been needed for many years. According to
the documentation for OpenSSL and GnuTLS they are thread-safe by design,
assuming support for the underlying OS threading API is built-in.

Ref: https://github.com/curl/curl/pull/13850#issuecomment-2143538458

Closes https://github.com/curl/curl/pull/13851

diff --git a/docs/examples/threaded-ssl.c b/docs/examples/threaded-ssl.c
index f58e447412a0968085a252018e2d3989d1586a19..5f287460da41cbbcafcb4b18180b83fbb535f002 100644 (file)
--- a/docs/examples/threaded-ssl.c
+++ b/docs/examples/threaded-ssl.c
@@ -27,13 +27,13 @@
  * </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.
+ * once over HTTPS.
  *
- * 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
+ * Recent versions of OpenSSL and GnuTLS are thread safe by design, assuming
+ * support for the underlying OS threading API is built-in. Older revisions
+ * of this example demonstrated locking callbacks for the SSL library, which
+ * are no longer necessary. An older revision with callbacks can be found at
+ * https://github.com/curl/curl/blob/curl-7_88_1/docs/examples/threaded-ssl.c
  */
 
 #define USE_OPENSSL /* or USE_GNUTLS accordingly */
@@ -44,71 +44,6 @@
 
 #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/",
@@ -143,8 +78,6 @@ int main(int argc, char **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 */
@@ -162,7 +95,5 @@ int main(int argc, char **argv)
     fprintf(stderr, "Thread %d terminated\n", i);
   }
 
-  kill_locks();
-
   return 0;
 }