flux-dump: internally use array instead of list

Problem: In the near future we may wish to asynchronously
load blobrefs to increase parallelization.  This can lead to
RPCs responding out of order, so using a list and appending to
it will not work for storing responses.

Convert from using a msglist to a simple array to store responses.

Author: chu11

src/cmd/builtin/dump.c

@@ -162,7 +162,7 @@ static void dump_valref (struct archive *ar,
                          json_t *treeobj)
 {
     int count = treeobj_get_count (treeobj);
-    struct flux_msglist *l;
+    const flux_msg_t **msgs;
     const flux_msg_t *msg;
     int total_size = 0;
     struct archive_entry *entry;
@@ -183,8 +183,8 @@ static void dump_valref (struct archive *ar,
      * retaining the futures for a second pass, just retain references to the
      * content.load response messages.
      */
-    if (!(l = flux_msglist_create ()))
-        log_err_exit ("could not create message list");
+    if (!(msgs = calloc (count, sizeof (msg))))
+        log_err_exit ("could not create messages array");
     for (int i = 0; i < count; i++) {
         flux_future_t *f;
         if (!(f = content_load_byblobref (h,
@@ -197,11 +197,12 @@ static void dump_valref (struct archive *ar,
                         i,
                         future_strerror (f, errno));
             flux_future_destroy (f);
-            flux_msglist_destroy (l);
+            for (int j = 0; j < i; j++)
+                flux_msg_decref (msgs[j]);
+            free (msgs);
             return;
         }
-        if (flux_msglist_append (l, msg) < 0)
-            log_err_exit ("could not stash load response message");
+        msgs[i] = flux_msg_incref (msg);
         total_size += len;
         flux_future_destroy (f);
     }
@@ -217,16 +218,16 @@ static void dump_valref (struct archive *ar,
 
     if (archive_write_header (ar, entry) != ARCHIVE_OK)
         log_msg_exit ("%s", archive_error_string (ar));
-    while ((msg = flux_msglist_pop (l))) {
-        if (flux_response_decode_raw (msg, NULL, &data, &len) < 0)
+    for (int i = 0; i < count; i++) {
+        if (flux_response_decode_raw (msgs[i], NULL, &data, &len) < 0)
             log_err_exit ("error processing stashed valref responses");
         if (len > 0)
             dump_write_data (ar, data, len);
-        flux_msg_decref (msg);
+        flux_msg_decref (msgs[i]);
     }
     archive_entry_free (entry);
     progress (h, 1);
-    flux_msglist_destroy (l);
+    free (msgs);
 }
 
 static void dump_val (struct archive *ar,