Re: [PATCH 2/8] commit-graph.c: show progress of finding reachable commits

> When 'git commit-graph write --reachable' is invoked, the commit-graph
> machinery calls 'for_each_ref()' to discover the set of reachable
> commits.
> 
> Right now the 'add_ref_to_set' callback is not doing anything other than
> adding an OID to the set of known-reachable OIDs. In a subsequent
> commit, 'add_ref_to_set' will presumptively peel references. This
> operation should be fast for repositories with an up-to-date
> '$GIT_DIR/packed-refs', but may be slow in the general case.
> 
> So that it doesn't appear that 'git commit-graph write' is idling with
> '--reachable' in the slow case, add a progress meter to provide some
> output in the meantime.
> 
> In general, we don't expect a progress meter to appear at all, since
> peeling references with a 'packed-refs' file is quick. If it's slow and
> we do show a progress meter, the subsequent 'fill_oids_from_commits()'
> will be fast, since all of the calls to
> 'lookup_commit_reference_gently()' will be no-ops.
> 
> Both progress meters are delayed, so it is unlikely that more than one
> will appear. In either case, this intermediate state will go away in a
> handful of patches, at which point there will be at most one progress
> meter.
> 
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
>  commit-graph.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/commit-graph.c b/commit-graph.c
> index 00da281f39..8f61256b0a 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -1320,6 +1320,7 @@ static void compute_bloom_filters(struct write_commit_graph_context *ctx)
>  
>  struct refs_cb_data {
>  	struct oidset *commits;
> +	struct progress *progress;
>  };
>  
>  static int add_ref_to_set(const char *refname,
> @@ -1328,6 +1329,8 @@ static int add_ref_to_set(const char *refname,
>  {
>  	struct refs_cb_data *data = (struct refs_cb_data *)cb_data;
>  
> +	display_progress(data->progress, oidset_size(data->commits) + 1);
> +
>  	oidset_insert(data->commits, oid);
>  	return 0;
>  }
> @@ -1342,12 +1345,17 @@ int write_commit_graph_reachable(struct object_directory *odb,
>  
>  	memset(&data, 0, sizeof(data));
>  	data.commits = &commits;
> +	if (flags & COMMIT_GRAPH_WRITE_PROGRESS)
> +		data.progress = start_delayed_progress(
> +			_("Finding reachable commits"), 0);