Revert "multi: remove PENDING + MSGSENT handles from the main linked list"

This reverts commit f6d6f3ce01.

The commits caused issues in the 8.0.0 release. Needs a retake.

Reported-by: Kamil Dudka
Closes #10795

lib/multi.c

@@ -383,10 +383,12 @@ static void sh_init(struct Curl_hash *hash, int hashsize)
  * Called when a transfer is completed. Adds the given msg pointer to
  * the list kept in the multi handle.
  */
-static void multi_addmsg(struct Curl_multi *multi, struct Curl_message *msg)
+static CURLMcode multi_addmsg(struct Curl_multi *multi,
+                              struct Curl_message *msg)
 {
   Curl_llist_insert_next(&multi->msglist, multi->msglist.tail, msg,
                          &msg->list);
+  return CURLM_OK;
 }
 
 struct Curl_multi *Curl_multi_handle(int hashsize, /* socket hash */
@@ -409,7 +411,6 @@ struct Curl_multi *Curl_multi_handle(int hashsize, /* socket hash */
 
   Curl_llist_init(&multi->msglist, NULL);
   Curl_llist_init(&multi->pending, NULL);
-  Curl_llist_init(&multi->msgsent, NULL);
 
   multi->multiplexing = TRUE;
 
@@ -455,14 +456,6 @@ struct Curl_multi *curl_multi_init(void)
                            CURL_DNS_HASH_SIZE);
 }
 
-/* returns TRUE if the easy handle is supposed to be present in the main link
-   list */
-static bool in_main_list(struct Curl_easy *data)
-{
-  return ((data->mstate != MSTATE_PENDING) &&
-          (data->mstate != MSTATE_MSGSENT));
-}
-
 static void link_easy(struct Curl_multi *multi,
                       struct Curl_easy *data)
 {
@@ -496,8 +489,6 @@ static void unlink_easy(struct Curl_multi *multi,
     data->next->prev = data->prev;
   else
     multi->easylp = data->prev; /* point to last node */
-
-  data->prev = data->next = NULL;
 }
 
 
@@ -857,16 +848,10 @@ CURLMcode curl_multi_remove_handle(struct Curl_multi *multi,
      called. Do it after multi_done() in case that sets another time! */
   Curl_expire_clear(data);
 
-  if(data->connect_queue.ptr) {
-    /* the handle is in the pending or msgsent lists, so go ahead and remove
-       it */
-    if(data->mstate == MSTATE_PENDING)
-      Curl_llist_remove(&multi->pending, &data->connect_queue, NULL);
-    else
-      Curl_llist_remove(&multi->msgsent, &data->connect_queue, NULL);
-  }
-  if(in_main_list(data))
-    unlink_easy(multi, data);
+  if(data->connect_queue.ptr)
+    /* the handle was in the pending list waiting for an available connection,
+       so go ahead and remove it */
+    Curl_llist_remove(&multi->pending, &data->connect_queue, NULL);
 
   if(data->dns.hostcachetype == HCACHE_MULTI) {
     /* stop using the multi handle's DNS cache, *after* the possible
@@ -927,6 +912,7 @@ CURLMcode curl_multi_remove_handle(struct Curl_multi *multi,
 
   /* make sure there's no pending message in the queue sent from this easy
      handle */
+
   for(e = multi->msglist.head; e; e = e->next) {
     struct Curl_message *msg = e->ptr;
 
@@ -937,6 +923,19 @@ CURLMcode curl_multi_remove_handle(struct Curl_multi *multi,
     }
   }
 
+  /* Remove from the pending list if it is there. Otherwise this will
+     remain on the pending list forever due to the state change. */
+  for(e = multi->pending.head; e; e = e->next) {
+    struct Curl_easy *curr_data = e->ptr;
+
+    if(curr_data == data) {
+      Curl_llist_remove(&multi->pending, e, NULL);
+      break;
+    }
+  }
+
+  unlink_easy(multi, data);
+
   /* NOTE NOTE NOTE
      We do not touch the easy handle here! */
   multi->num_easy--; /* one less to care about now */
@@ -1944,6 +1943,11 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
       }
       break;
 
+    case MSTATE_PENDING:
+      /* We will stay here until there is a connection available. Then
+         we try again in the MSTATE_CONNECT state. */
+      break;
+
     case MSTATE_CONNECT:
       /* Connect. We want to get a connection identifier filled in. */
       /* init this transfer. */
@@ -1967,8 +1971,6 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
         /* add this handle to the list of connect-pending handles */
         Curl_llist_insert_next(&multi->pending, multi->pending.tail, data,
                                &data->connect_queue);
-        /* unlink from the main list */
-        unlink_easy(multi, data);
         result = CURLE_OK;
         break;
       }
@@ -2595,11 +2597,9 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
     case MSTATE_COMPLETED:
       break;
 
-    case MSTATE_PENDING:
     case MSTATE_MSGSENT:
-      /* handles in these states should NOT be in this list */
-      DEBUGASSERT(0);
-      break;
+      data->result = result;
+      return CURLM_OK; /* do nothing */
 
     default:
       return CURLM_INTERNAL_ERROR;
@@ -2687,17 +2687,10 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
         msg->extmsg.easy_handle = data;
         msg->extmsg.data.result = result;
 
-        multi_addmsg(multi, msg);
+        rc = multi_addmsg(multi, msg);
         DEBUGASSERT(!data->conn);
       }
       multistate(data, MSTATE_MSGSENT);
-
-      /* add this handle to the list of msgsent handles */
-      Curl_llist_insert_next(&multi->msgsent, multi->msgsent.tail, data,
-                             &data->connect_queue);
-      /* unlink from the main list */
-      unlink_easy(multi, data);
-      return CURLM_OK;
     }
   } while((rc == CURLM_CALL_MULTI_PERFORM) || multi_ischanged(multi, FALSE));
 
@@ -2728,9 +2721,6 @@ CURLMcode curl_multi_perform(struct Curl_multi *multi, int *running_handles)
     /* Do the loop and only alter the signal ignore state if the next handle
        has a different NO_SIGNAL state than the previous */
     do {
-      /* the current node might be unlinked in multi_runsingle(), get the next
-         pointer now */
-      struct Curl_easy *datanext = data->next;
       if(data->set.no_signal != nosig) {
         sigpipe_restore(&pipe_st);
         sigpipe_ignore(data, &pipe_st);
@@ -2739,7 +2729,7 @@ CURLMcode curl_multi_perform(struct Curl_multi *multi, int *running_handles)
       result = multi_runsingle(multi, &now, data);
       if(result)
         returncode = result;
-      data = datanext; /* operate on next handle */
+      data = data->next; /* operate on next handle */
     } while(data);
     sigpipe_restore(&pipe_st);
   }
@@ -3720,9 +3710,6 @@ static void process_pending_handles(struct Curl_multi *multi)
 
     DEBUGASSERT(data->mstate == MSTATE_PENDING);
 
-    /* put it back into the main list */
-    link_easy(multi, data);
-
     multistate(data, MSTATE_CONNECT);
 
     /* Remove this node from the list */

lib/multihandle.h

@@ -101,8 +101,6 @@ struct Curl_multi {
 
   struct Curl_llist pending; /* Curl_easys that are in the
                                 MSTATE_PENDING state */
-  struct Curl_llist msgsent; /* Curl_easys that are in the
-                                MSTATE_MSGSENT state */
 
   /* callback function and user data pointer for the *socket() API */
   curl_socket_callback socket_cb;

lib/urldata.h

@@ -1894,8 +1894,7 @@ struct Curl_easy {
   struct Curl_easy *prev;
 
   struct connectdata *conn;
-  struct Curl_llist_element connect_queue; /* for the pending and msgsent
-                                              lists */
+  struct Curl_llist_element connect_queue;
   struct Curl_llist_element conn_queue; /* list per connectdata */
 
   CURLMstate mstate;  /* the handle's state */