commit-graph: compute generation numbers

While preparing commits to be written into a commit-graph file, compute
the generation numbers using a depth-first strategy.

The only commits that are walked in this depth-first search are those
without a precomputed generation number. Thus, computation time will be
relative to the number of new commits to the commit-graph file.

If a computed generation number would exceed GENERATION_NUMBER_MAX, then
use GENERATION_NUMBER_MAX instead.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit-graph.c b/commit-graph.c
index 9ad21c3ffb6fb0104deba7e8fed12972351ce51b..36d765e10a95708029ad7a003bf67cd0d9231838 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -439,6 +439,8 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
                else
                        packedDate[0] = 0;
 
+               packedDate[0] |= htonl((*list)->generation << 2);
+
                packedDate[1] = htonl((*list)->date);
                hashwrite(f, packedDate, 8);
 
@@ -571,6 +573,45 @@ static void close_reachable(struct packed_oid_list *oids)
        }
 }
 
+static void compute_generation_numbers(struct packed_commit_list* commits)
+{
+       int i;
+       struct commit_list *list = NULL;
+
+       for (i = 0; i < commits->nr; i++) {
+               if (commits->list[i]->generation != GENERATION_NUMBER_INFINITY &&
+                   commits->list[i]->generation != GENERATION_NUMBER_ZERO)
+                       continue;
+
+               commit_list_insert(commits->list[i], &list);
+               while (list) {
+                       struct commit *current = list->item;
+                       struct commit_list *parent;
+                       int all_parents_computed = 1;
+                       uint32_t max_generation = 0;
+
+                       for (parent = current->parents; parent; parent = parent->next) {
+                               if (parent->item->generation == GENERATION_NUMBER_INFINITY ||
+                                   parent->item->generation == GENERATION_NUMBER_ZERO) {
+                                       all_parents_computed = 0;
+                                       commit_list_insert(parent->item, &list);
+                                       break;
+                               } else if (parent->item->generation > max_generation) {
+                                       max_generation = parent->item->generation;
+                               }
+                       }
+
+                       if (all_parents_computed) {
+                               current->generation = max_generation + 1;
+                               pop_commit(&list);
+
+                               if (current->generation > GENERATION_NUMBER_MAX)
+                                       current->generation = GENERATION_NUMBER_MAX;
+                       }
+               }
+       }
+}
+
 void write_commit_graph(const char *obj_dir,
                        const char **pack_indexes,
                        int nr_packs,
@@ -694,6 +735,8 @@ void write_commit_graph(const char *obj_dir,
        if (commits.nr >= GRAPH_PARENT_MISSING)
                die(_("too many commits to write graph"));
 
+       compute_generation_numbers(&commits);
+
        graph_name = get_commit_graph_filename(obj_dir);
        fd = hold_lock_file_for_update(&lk, graph_name, 0);