docs/examples: use curl_multi_poll() in multi examples

The API is soon two years old and deserves being shown as the primary
way to drive multi code as it makes it much easier to write code.

multi-poll: removed

multi-legacy: add to show how we did multi API use before
curl_multi_wait/poll.

Closes #7352

docs/examples/multi-legacy.c

@@ -0,0 +1,177 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2021, 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>
+ * A basic application source code using the multi interface doing two
+ * transfers in parallel without curl_multi_wait/poll.
+ * </DESC>
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+/* somewhat unix-specific */
+#include <sys/time.h>
+#include <unistd.h>
+
+/* curl stuff */
+#include <curl/curl.h>
+
+/*
+ * Download a HTTP file and upload an FTP file simultaneously.
+ */
+
+#define HANDLECOUNT 2   /* Number of simultaneous transfers */
+#define HTTP_HANDLE 0   /* Index for the HTTP transfer */
+#define FTP_HANDLE 1    /* Index for the FTP transfer */
+
+int main(void)
+{
+  CURL *handles[HANDLECOUNT];
+  CURLM *multi_handle;
+
+  int still_running = 0; /* keep number of running handles */
+  int i;
+
+  CURLMsg *msg; /* for picking up messages with the transfer status */
+  int msgs_left; /* how many messages are left */
+
+  /* Allocate one CURL handle per transfer */
+  for(i = 0; i<HANDLECOUNT; i++)
+    handles[i] = curl_easy_init();
+
+  /* set the options (I left out a few, you'll get the point anyway) */
+  curl_easy_setopt(handles[HTTP_HANDLE], CURLOPT_URL, "https://example.com");
+
+  curl_easy_setopt(handles[FTP_HANDLE], CURLOPT_URL, "ftp://example.com");
+  curl_easy_setopt(handles[FTP_HANDLE], CURLOPT_UPLOAD, 1L);
+
+  /* init a multi stack */
+  multi_handle = curl_multi_init();
+
+  /* add the individual transfers */
+  for(i = 0; i<HANDLECOUNT; i++)
+    curl_multi_add_handle(multi_handle, handles[i]);
+
+  /* we start some action by calling perform right away */
+  curl_multi_perform(multi_handle, &still_running);
+
+  while(still_running) {
+    struct timeval timeout;
+    int rc; /* select() return code */
+    CURLMcode mc; /* curl_multi_fdset() return code */
+
+    fd_set fdread;
+    fd_set fdwrite;
+    fd_set fdexcep;
+    int maxfd = -1;
+
+    long curl_timeo = -1;
+
+    FD_ZERO(&fdread);
+    FD_ZERO(&fdwrite);
+    FD_ZERO(&fdexcep);
+
+    /* set a suitable timeout to play around with */
+    timeout.tv_sec = 1;
+    timeout.tv_usec = 0;
+
+    curl_multi_timeout(multi_handle, &curl_timeo);
+    if(curl_timeo >= 0) {
+      timeout.tv_sec = curl_timeo / 1000;
+      if(timeout.tv_sec > 1)
+        timeout.tv_sec = 1;
+      else
+        timeout.tv_usec = (curl_timeo % 1000) * 1000;
+    }
+
+    /* get file descriptors from the transfers */
+    mc = curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
+
+    if(mc != CURLM_OK) {
+      fprintf(stderr, "curl_multi_fdset() failed, code %d.\n", mc);
+      break;
+    }
+
+    /* On success the value of maxfd is guaranteed to be >= -1. We call
+       select(maxfd + 1, ...); specially in case of (maxfd == -1) there are
+       no fds ready yet so we call select(0, ...) --or Sleep() on Windows--
+       to sleep 100ms, which is the minimum suggested value in the
+       curl_multi_fdset() doc. */
+
+    if(maxfd == -1) {
+#ifdef _WIN32
+      Sleep(100);
+      rc = 0;
+#else
+      /* Portable sleep for platforms other than Windows. */
+      struct timeval wait = { 0, 100 * 1000 }; /* 100ms */
+      rc = select(0, NULL, NULL, NULL, &wait);
+#endif
+    }
+    else {
+      /* Note that on some platforms 'timeout' may be modified by select().
+         If you need access to the original value save a copy beforehand. */
+      rc = select(maxfd + 1, &fdread, &fdwrite, &fdexcep, &timeout);
+    }
+
+    switch(rc) {
+    case -1:
+      /* select error */
+      break;
+    case 0: /* timeout */
+    default: /* action */
+      curl_multi_perform(multi_handle, &still_running);
+      break;
+    }
+  }
+
+  /* See how the transfers went */
+  while((msg = curl_multi_info_read(multi_handle, &msgs_left))) {
+    if(msg->msg == CURLMSG_DONE) {
+      int idx;
+
+      /* Find out which handle this message is about */
+      for(idx = 0; idx<HANDLECOUNT; idx++) {
+        int found = (msg->easy_handle == handles[idx]);
+        if(found)
+          break;
+      }
+
+      switch(idx) {
+      case HTTP_HANDLE:
+        printf("HTTP transfer completed with status %d\n", msg->data.result);
+        break;
+      case FTP_HANDLE:
+        printf("FTP transfer completed with status %d\n", msg->data.result);
+        break;
+      }
+    }
+  }
+
+  curl_multi_cleanup(multi_handle);
+
+  /* Free the CURL handles */
+  for(i = 0; i<HANDLECOUNT; i++)
+    curl_easy_cleanup(handles[i]);
+
+  return 0;
+}