examples/10-at-a-time.c: improve readability and simplify

 - use better variable names to explain their purposes
 - convert logic to curl_multi_wait()

1 files changed, 25 insertions, 72 deletions

diff --git a/docs/examples/10-at-a-time.c b/docs/examples/10-at-a-time.c
index 638f425f2..2b7497616 100644
--- a/docs/examples/10-at-a-time.c
+++ b/docs/examples/10-at-a-time.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2019, 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
@@ -20,10 +20,8 @@
  *
  ***************************************************************************/
 /* <DESC>
- * Source code using the multi interface to download many
- * files, with a capped maximum amount of simultaneous transfers.
+ * Download many files in parallel, in the same thread.
  * </DESC>
- * Written by Michael Wallner
  */
 
 #include <errno.h>
@@ -84,27 +82,23 @@ static const char *urls[] = {
   "https://www.un.org",
 };
 
-#define MAX 10 /* number of simultaneous transfers */
-#define CNT sizeof(urls)/sizeof(char *) /* total number of transfers to do */
+#define MAX_PARALLEL 10 /* number of simultaneous transfers */
+#define NUM_URLS sizeof(urls)/sizeof(char *) /* total number of transfers to do */
 
-static size_t cb(char *d, size_t n, size_t l, void *p)
+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)d;
-  (void)p;
+  (void)data;
+  (void)userp;
   return n*l;
 }
 
-static void init(CURLM *cm, int i)
+static void add_transfer(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_WRITEFUNCTION, write_cb);
   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);
 }
 
@@ -112,64 +106,23 @@ 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;
+  unsigned int transfers = 0;
+  int msgs_left = -1;
+  int still_alive = 1;
 
   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);
+  /* Limit the amount of simultaneous connections curl should allow: */
+  curl_multi_setopt(cm, CURLMOPT_MAXCONNECTS, (long)MAX_PARALLEL);
 
-  for(C = 0; C < MAX; ++C) {
-    init(cm, C);
-  }
+  for(transfers = 0; transfers < MAX_PARALLEL; transfers++)
+    add_transfer(cm, transfers);
 
-  while(U) {
-    curl_multi_perform(cm, &U);
+  do {
+    curl_multi_perform(cm, &still_alive);
 
-    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((unsigned int)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))) {
+    while((msg = curl_multi_info_read(cm, &msgs_left))) {
       if(msg->msg == CURLMSG_DONE) {
         char *url;
         CURL *e = msg->easy_handle;
@@ -182,13 +135,13 @@ int main(void)
       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 */
-      }
+      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();