diff: improve lifecycle management of diff queues

The lifecycle management of diff queues is somewhat confusing:

  - For most of the part this can be attributed to `DIFF_QUEUE_CLEAR()`,
    which does not release any memory but rather initializes the queue,
    only. This is in contrast to our common naming schema, where
    "clearing" means that we release underlying memory and then
    re-initialize the data structure such that it is ready to use.

  - A second offender is `diff_free_queue()`, which does not free the
    queue structure itself. It is rather a release-style function.

Refactor the code to make things less confusing. `DIFF_QUEUE_CLEAR()` is
replaced by `DIFF_QUEUE_INIT` and `diff_queue_init()`, while
`diff_free_queue()` is replaced by `diff_queue_release()`. While on it,
adapt callsites where we call `DIFF_QUEUE_CLEAR()` with the intent to
release underlying memory to instead call `diff_queue_clear()` to fix
memory leaks.

This memory leak is exposed by t4211, but plugging it alone does not
make the whole test suite pass.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bloom.c

@@ -476,8 +476,6 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
 				*last_slash = '\0';
 
 			} while (*path);
-
-			diff_free_filepair(diff_queued_diff.queue[i]);
 		}
 
 		if (hashmap_get_size(&pathmap) > settings->max_changed_paths) {
@@ -508,8 +506,6 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
 	cleanup:
 		hashmap_clear_and_free(&pathmap, struct pathmap_hash_entry, entry);
 	} else {
-		for (i = 0; i < diff_queued_diff.nr; i++)
-			diff_free_filepair(diff_queued_diff.queue[i]);
 		init_truncated_large_filter(filter, settings->hash_version);
 
 		if (computed)
@@ -519,9 +515,7 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
 	if (computed)
 		*computed |= BLOOM_COMPUTED;
 
-	free(diff_queued_diff.queue);
-	DIFF_QUEUE_CLEAR(&diff_queued_diff);
-
+	diff_queue_clear(&diff_queued_diff);
 	return filter;
 }
 

diff.c

@@ -5983,11 +5983,18 @@ void diff_free_filepair(struct diff_filepair *p)
 	free(p);
 }
 
-void diff_free_queue(struct diff_queue_struct *q)
+void diff_queue_init(struct diff_queue_struct *q)
+{
+	struct diff_queue_struct blank = DIFF_QUEUE_INIT;
+	memcpy(q, &blank, sizeof(*q));
+}
+
+void diff_queue_clear(struct diff_queue_struct *q)
 {
 	for (int i = 0; i < q->nr; i++)
 		diff_free_filepair(q->queue[i]);
 	free(q->queue);
+	diff_queue_init(q);
 }
 
 const char *diff_aligned_abbrev(const struct object_id *oid, int len)
@@ -6551,8 +6558,7 @@ int diff_flush_patch_id(struct diff_options *options, struct object_id *oid, int
 	struct diff_queue_struct *q = &diff_queued_diff;
 	int result = diff_get_patch_id(options, oid, diff_header_only);
 
-	diff_free_queue(q);
-	DIFF_QUEUE_CLEAR(q);
+	diff_queue_clear(q);
 
 	return result;
 }
@@ -6835,8 +6841,7 @@ void diff_flush(struct diff_options *options)
 	}
 
 free_queue:
-	diff_free_queue(q);
-	DIFF_QUEUE_CLEAR(q);
+	diff_queue_clear(q);
 	diff_free(options);
 
 	/*
@@ -6867,9 +6872,7 @@ static void diffcore_apply_filter(struct diff_options *options)
 {
 	int i;
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct diff_queue_struct outq;
-
-	DIFF_QUEUE_CLEAR(&outq);
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 
 	if (!options->filter)
 		return;
@@ -6962,8 +6965,7 @@ static void diffcore_skip_stat_unmatch(struct diff_options *diffopt)
 {
 	int i;
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct diff_queue_struct outq;
-	DIFF_QUEUE_CLEAR(&outq);
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];

diffcore-break.c

@@ -131,7 +131,7 @@ static int should_break(struct repository *r,
 void diffcore_break(struct repository *r, int break_score)
 {
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct diff_queue_struct outq;
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 
 	/* When the filepair has this much edit (insert and delete),
 	 * it is first considered to be a rewrite and broken into a
@@ -178,8 +178,6 @@ void diffcore_break(struct repository *r, int break_score)
 	if (!merge_score)
 		merge_score = DEFAULT_MERGE_SCORE;
 
-	DIFF_QUEUE_CLEAR(&outq);
-
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 		int score;
@@ -275,11 +273,9 @@ static void merge_broken(struct diff_filepair *p,
 void diffcore_merge_broken(void)
 {
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct diff_queue_struct outq;
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 	int i, j;
 
-	DIFF_QUEUE_CLEAR(&outq);
-
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 		if (!p)

diffcore-pickaxe.c

@@ -182,9 +182,7 @@ static void pickaxe(struct diff_queue_struct *q, struct diff_options *o,
 		    regex_t *regexp, kwset_t kws, pickaxe_fn fn)
 {
 	int i;
-	struct diff_queue_struct outq;
-
-	DIFF_QUEUE_CLEAR(&outq);
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 
 	if (o->pickaxe_opts & DIFF_PICKAXE_ALL) {
 		/* Showing the whole changeset if needle exists */

diffcore-rename.c

@@ -1388,7 +1388,7 @@ void diffcore_rename_extended(struct diff_options *options,
 	int detect_rename = options->detect_rename;
 	int minimum_score = options->rename_score;
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct diff_queue_struct outq;
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 	struct diff_score *mx;
 	int i, j, rename_count, skip_unmodified = 0;
 	int num_destinations, dst_cnt;
@@ -1638,7 +1638,6 @@ void diffcore_rename_extended(struct diff_options *options,
 	 * are recorded in rename_dst.  The original list is still in *q.
 	 */
 	trace2_region_enter("diff", "write back to queue", options->repo);
-	DIFF_QUEUE_CLEAR(&outq);
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 		struct diff_filepair *pair_to_free = NULL;

diffcore-rotate.c

@@ -10,7 +10,7 @@
 void diffcore_rotate(struct diff_options *opt)
 {
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct diff_queue_struct outq;
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 	int rotate_to, i;
 
 	if (!q->nr)
@@ -31,7 +31,6 @@ void diffcore_rotate(struct diff_options *opt)
 		return;
 	}
 
-	DIFF_QUEUE_CLEAR(&outq);
 	rotate_to = i;
 
 	for (i = rotate_to; i < q->nr; i++)

diffcore.h

@@ -153,18 +153,16 @@ struct diff_queue_struct {
 	int nr;
 };
 
-#define DIFF_QUEUE_CLEAR(q) \
-	do { \
-		(q)->queue = NULL; \
-		(q)->nr = (q)->alloc = 0; \
-	} while (0)
+#define DIFF_QUEUE_INIT { 0 }
+
+void diff_queue_init(struct diff_queue_struct *q);
+void diff_queue_clear(struct diff_queue_struct *q);
 
 extern struct diff_queue_struct diff_queued_diff;
 struct diff_filepair *diff_queue(struct diff_queue_struct *,
 				 struct diff_filespec *,
 				 struct diff_filespec *);
 void diff_q(struct diff_queue_struct *, struct diff_filepair *);
-void diff_free_queue(struct diff_queue_struct *q);
 
 /* dir_rename_relevance: the reason we want rename information for a dir */
 enum dir_rename_relevance {

line-log.c

@@ -787,15 +787,14 @@ static void move_diff_queue(struct diff_queue_struct *dst,
 			    struct diff_queue_struct *src)
 {
 	assert(src != dst);
-	memcpy(dst, src, sizeof(struct diff_queue_struct));
-	DIFF_QUEUE_CLEAR(src);
+	memcpy(dst, src, sizeof(*dst));
+	diff_queue_init(src);
 }
 
 static void filter_diffs_for_paths(struct line_log_data *range, int keep_deletions)
 {
 	int i;
-	struct diff_queue_struct outq;
-	DIFF_QUEUE_CLEAR(&outq);
+	struct diff_queue_struct outq = DIFF_QUEUE_INIT;
 
 	for (i = 0; i < diff_queued_diff.nr; i++) {
 		struct diff_filepair *p = diff_queued_diff.queue[i];
@@ -850,12 +849,12 @@ static void queue_diffs(struct line_log_data *range,
 		clear_pathspec(&opt->pathspec);
 		parse_pathspec_from_ranges(&opt->pathspec, range);
 	}
-	DIFF_QUEUE_CLEAR(&diff_queued_diff);
+	diff_queue_clear(&diff_queued_diff);
 	diff_tree_oid(parent_tree_oid, tree_oid, "", opt);
 	if (opt->detect_rename && diff_might_be_rename()) {
 		/* must look at the full tree diff to detect renames */
 		clear_pathspec(&opt->pathspec);
-		DIFF_QUEUE_CLEAR(&diff_queued_diff);
+		diff_queue_clear(&diff_queued_diff);
 
 		diff_tree_oid(parent_tree_oid, tree_oid, "", opt);
 
@@ -1097,7 +1096,7 @@ static struct diff_filepair *diff_filepair_dup(struct diff_filepair *pair)
 static void free_diffqueues(int n, struct diff_queue_struct *dq)
 {
 	for (int i = 0; i < n; i++)
-		diff_free_queue(&dq[i]);
+		diff_queue_clear(&dq[i]);
 	free(dq);
 }
 
@@ -1200,7 +1199,7 @@ static int process_ranges_ordinary_commit(struct rev_info *rev, struct commit *c
 	if (parent)
 		add_line_range(rev, parent, parent_range);
 	free_line_log_data(parent_range);
-	diff_free_queue(&queue);
+	diff_queue_clear(&queue);
 	return changed;
 }
 

log-tree.c

@@ -675,7 +675,7 @@ static void show_diff_of_diff(struct rev_info *opt)
 		struct diff_queue_struct dq;
 
 		memcpy(&dq, &diff_queued_diff, sizeof(diff_queued_diff));
-		DIFF_QUEUE_CLEAR(&diff_queued_diff);
+		diff_queue_init(&diff_queued_diff);
 
 		fprintf_ln(opt->diffopt.file, "\n%s", opt->idiff_title);
 		show_interdiff(opt->idiff_oid1, opt->idiff_oid2, 2,
@@ -694,7 +694,7 @@ static void show_diff_of_diff(struct rev_info *opt)
 		};
 
 		memcpy(&dq, &diff_queued_diff, sizeof(diff_queued_diff));
-		DIFF_QUEUE_CLEAR(&diff_queued_diff);
+		diff_queue_init(&diff_queued_diff);
 
 		fprintf_ln(opt->diffopt.file, "\n%s", opt->rdiff_title);
 		/*

merge-ort.c

@@ -3536,7 +3536,7 @@ static int detect_and_process_renames(struct merge_options *opt)
 	/* Free memory for renames->pairs[] and combined */
 	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
 		free(renames->pairs[s].queue);
-		DIFF_QUEUE_CLEAR(&renames->pairs[s]);
+		diff_queue_init(&renames->pairs[s]);
 	}
 	for (i = 0; i < combined.nr; i++)
 		pool_diff_free_filepair(&opt->priv->pool, combined.queue[i]);