ref-filter.c: filter & format refs in the same callback

Update 'filter_and_format_refs()' to try to perform ref filtering &
formatting in a single ref iteration, without an intermediate 'struct
ref_array'. This can only be done if no operations need to be performed on a
pre-filtered array; specifically, if the refs are

- filtered on reachability,
- sorted, or
- formatted with ahead-behind information

they cannot be filtered & formatted in the same iteration. In that case,
fall back on the current filter-then-sort-then-format flow.

This optimization substantially improves memory usage due to no longer
storing a ref array in memory. In some cases, it also dramatically reduces
runtime (e.g. 'git for-each-ref --no-sort --count=1', which no longer loads
all refs into a 'struct ref_array' to printing only the first ref).

Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/ref-filter.c b/ref-filter.c
index 8bfdc66e447212488c1de2469ad7af644b7efa93..ca4ebed4eb4ec5183eb3ad5d6dda22470dd05a8c 100644 (file)
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -2779,6 +2779,49 @@ static void free_array_item(struct ref_array_item *item)
        free(item);
 }
 
+struct ref_filter_and_format_cbdata {
+       struct ref_filter *filter;
+       struct ref_format *format;
+
+       struct ref_filter_and_format_internal {
+               int count;
+       } internal;
+};
+
+static int filter_and_format_one(const char *refname, const struct object_id *oid, int flag, void *cb_data)
+{
+       struct ref_filter_and_format_cbdata *ref_cbdata = cb_data;
+       struct ref_array_item *ref;
+       struct strbuf output = STRBUF_INIT, err = STRBUF_INIT;
+
+       ref = apply_ref_filter(refname, oid, flag, ref_cbdata->filter);
+       if (!ref)
+               return 0;
+
+       if (format_ref_array_item(ref, ref_cbdata->format, &output, &err))
+               die("%s", err.buf);
+
+       if (output.len || !ref_cbdata->format->array_opts.omit_empty) {
+               fwrite(output.buf, 1, output.len, stdout);
+               putchar('\n');
+       }
+
+       strbuf_release(&output);
+       strbuf_release(&err);
+       free_array_item(ref);
+
+       /*
+        * Increment the running count of refs that match the filter. If
+        * max_count is set and we've reached the max, stop the ref
+        * iteration by returning a nonzero value.
+        */
+       if (ref_cbdata->format->array_opts.max_count &&
+           ++ref_cbdata->internal.count >= ref_cbdata->format->array_opts.max_count)
+               return 1;
+
+       return 0;
+}
+
 /* Free all memory allocated for ref_array */
 void ref_array_clear(struct ref_array *array)
 {
@@ -2962,16 +3005,49 @@ int filter_refs(struct ref_array *array, struct ref_filter *filter, unsigned int
        return ret;
 }
 
+static inline int can_do_iterative_format(struct ref_filter *filter,
+                                         struct ref_sorting *sorting,
+                                         struct ref_format *format)
+{
+       /*
+        * Filtering & formatting results within a single ref iteration
+        * callback is not compatible with options that require
+        * post-processing a filtered ref_array. These include:
+        * - filtering on reachability
+        * - sorting the filtered results
+        * - including ahead-behind information in the formatted output
+        */
+       return !(filter->reachable_from ||
+                filter->unreachable_from ||
+                sorting ||
+                format->bases.nr);
+}
+
 void filter_and_format_refs(struct ref_filter *filter, unsigned int type,
                            struct ref_sorting *sorting,
                            struct ref_format *format)
 {
-       struct ref_array array = { 0 };
-       filter_refs(&array, filter, type);
-       filter_ahead_behind(the_repository, format, &array);
-       ref_array_sort(sorting, &array);
-       print_formatted_ref_array(&array, format);
-       ref_array_clear(&array);
+       if (can_do_iterative_format(filter, sorting, format)) {
+               int save_commit_buffer_orig;
+               struct ref_filter_and_format_cbdata ref_cbdata = {
+                       .filter = filter,
+                       .format = format,
+               };
+
+               save_commit_buffer_orig = save_commit_buffer;
+               save_commit_buffer = 0;
+
+               do_filter_refs(filter, type, filter_and_format_one, &ref_cbdata);
+
+               save_commit_buffer = save_commit_buffer_orig;
+       } else {
+               struct ref_array array = { 0 };
+               filter_refs(&array, filter, type);
+               filter_ahead_behind(the_repository, format, &array);
+               ref_array_sort(sorting, &array);
+               print_formatted_ref_array(&array, format);
+               ref_array_clear(&array);
+       }
 }
 
 static int compare_detached_head(struct ref_array_item *a, struct ref_array_item *b)