Merge branch 'jk/stable-prio-queue'

* jk/stable-prio-queue:
t5539: update a flaky test
paint_down_to_common: use prio_queue
prio-queue: make output stable with respect to insertion
prio-queue: factor out compare and swap operations

diff --combined commit.c
index dce3d69dfdf5843b6dbae78a5c85a4060ca7604b,1fc60c01095a2dde8d5c7c7949efb0c2bff9c14d..2274e43fdfa03f2622cd3c461d65795af1ac2155
--- 1/commit.c
--- 2/commit.c
+++ b/commit.c
@@@ -18,6 -18,19 +18,6 @@@ int save_commit_buffer = 1
  
  const char *commit_type = "commit";
  
 -static struct commit *check_commit(struct object *obj,
 -                                 const unsigned char *sha1,
 -                                 int quiet)
 -{
 -      if (obj->type != OBJ_COMMIT) {
 -              if (!quiet)
 -                      error("Object %s is a %s, not a commit",
 -                            sha1_to_hex(sha1), typename(obj->type));
 -              return NULL;
 -      }
 -      return (struct commit *) obj;
 -}
 -
  struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
                                              int quiet)
  {
@@@ -25,7 -38,7 +25,7 @@@
  
        if (!obj)
                return NULL;
 -      return check_commit(obj, sha1, quiet);
 +      return object_as_type(obj, OBJ_COMMIT, quiet);
  }
  
  struct commit *lookup_commit_reference(const unsigned char *sha1)
@@@ -48,9 -61,13 +48,9 @@@ struct commit *lookup_commit_or_die(con
  struct commit *lookup_commit(const unsigned char *sha1)
  {
        struct object *obj = lookup_object(sha1);
 -      if (!obj) {
 -              struct commit *c = alloc_commit_node();
 -              return create_object(sha1, OBJ_COMMIT, c);
 -      }
 -      if (!obj->type)
 -              obj->type = OBJ_COMMIT;
 -      return check_commit(obj, sha1, 0);
 +      if (!obj)
 +              return create_object(sha1, alloc_commit_node());
 +      return object_as_type(obj, OBJ_COMMIT, 0);
  }
  
  struct commit *lookup_commit_reference_by_name(const char *name)
@@@ -430,7 -447,12 +430,7 @@@ struct commit_list *copy_commit_list(st
        struct commit_list *head = NULL;
        struct commit_list **pp = &head;
        while (list) {
 -              struct commit_list *new;
 -              new = xmalloc(sizeof(struct commit_list));
 -              new->item = list->item;
 -              new->next = NULL;
 -              *pp = new;
 -              pp = &new->next;
 +              pp = commit_list_append(list->item, pp);
                list = list->next;
        }
        return head;
@@@ -764,45 -786,41 +764,41 @@@ void sort_in_topological_order(struct c
  
  static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
  
- static struct commit *interesting(struct commit_list *list)
+ static int queue_has_nonstale(struct prio_queue *queue)
  {
-       while (list) {
-               struct commit *commit = list->item;
-               list = list->next;
-               if (commit->object.flags & STALE)
-                       continue;
-               return commit;
+       int i;
+       for (i = 0; i < queue->nr; i++) {
+               struct commit *commit = queue->array[i].data;
+               if (!(commit->object.flags & STALE))
+                       return 1;
        }
-       return NULL;
+       return 0;
  }
  
  /* all input commits in one and twos[] must have been parsed! */
  static struct commit_list *paint_down_to_common(struct commit *one, int n, struct commit **twos)
  {
-       struct commit_list *list = NULL;
+       struct prio_queue queue = { compare_commits_by_commit_date };
        struct commit_list *result = NULL;
        int i;
  
        one->object.flags |= PARENT1;
-       commit_list_insert_by_date(one, &list);
-       if (!n)
-               return list;
+       if (!n) {
+               commit_list_append(one, &result);
+               return result;
+       }
+       prio_queue_put(&queue, one);
+ 
        for (i = 0; i < n; i++) {
                twos[i]->object.flags |= PARENT2;
-               commit_list_insert_by_date(twos[i], &list);
+               prio_queue_put(&queue, twos[i]);
        }
  
-       while (interesting(list)) {
-               struct commit *commit;
+       while (queue_has_nonstale(&queue)) {
+               struct commit *commit = prio_queue_get(&queue);
                struct commit_list *parents;
-               struct commit_list *next;
                int flags;
  
-               commit = list->item;
-               next = list->next;
-               free(list);
-               list = next;
- 
                flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
                if (flags == (PARENT1 | PARENT2)) {
                        if (!(commit->object.flags & RESULT)) {
@@@ -821,11 -839,11 +817,11 @@@
                        if (parse_commit(p))
                                return NULL;
                        p->object.flags |= flags;
-                       commit_list_insert_by_date(p, &list);
+                       prio_queue_put(&queue, p);
                }
        }
  
-       free_commit_list(list);
+       clear_prio_queue(&queue);
        return result;
  }
  
@@@ -970,7 -988,12 +966,7 @@@ struct commit_list *get_merge_bases_man
        }
  
        /* There are more than one */
 -      cnt = 0;
 -      list = result;
 -      while (list) {
 -              list = list->next;
 -              cnt++;
 -      }
 +      cnt = commit_list_count(result);
        rslt = xcalloc(cnt, sizeof(*rslt));
        for (list = result, i = 0; list; list = list->next)
                rslt[i++] = list->item;
@@@ -1288,19 -1311,6 +1284,19 @@@ struct commit_extra_header *read_commit
        return extra;
  }
  
 +void for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data)
 +{
 +      struct commit_extra_header *extra, *to_free;
 +
 +      to_free = read_commit_extra_headers(commit, NULL);
 +      for (extra = to_free; extra; extra = extra->next) {
 +              if (strcmp(extra->key, "mergetag"))
 +                      continue; /* not a merge tag */
 +              fn(commit, extra, data);
 +      }
 +      free_commit_extra_headers(to_free);
 +}
 +
  static inline int standard_header_field(const char *field, size_t len)
  {
        return ((len == 4 && !memcmp(field, "tree ", 5)) ||