pack-bitmap: remove bitmap_git global variable

Remove the bitmap_git global variable. Instead, generate on demand an
instance of struct bitmap_index for code that needs to access it.

This allows us significant control over the lifetime of instances of
struct bitmap_index. In particular, packs can now be closed without
worrying if an unnecessarily long-lived "pack" field in struct
bitmap_index still points to it.

The bitmap API is also clearer in that we need to first obtain a struct
bitmap_index, then we use it.

This patch raises two potential issues: (1) memory for the struct
bitmap_index is allocated without being freed, and (2)
prepare_bitmap_git() and prepare_bitmap_walk() can reuse a previously
loaded bitmap. For (1), this will be dealt with in a subsequent patch in
this patch set that also deals with freeing the contents of the struct
bitmap_index (which were not freed previously, because they have global
scope). For (2), current bitmap users only load the bitmap once at most
(note that pack-objects can use bitmaps or write bitmaps, but not both
at the same time), so support for reuse has no effect - and future users
can pass around the struct bitmap_index * obtained if they need to do 2
or more things with the same bitmap.
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJonathan Tan <jonathantanmy@google.com>
Helped-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -2929,11 +2929,13 @@ static int pack_options_allow_reuse(void)
 
 static int get_object_list_from_bitmap(struct rev_info *revs)
 {
-	if (prepare_bitmap_walk(revs) < 0)
+	struct bitmap_index *bitmap_git;
+	if (!(bitmap_git = prepare_bitmap_walk(revs)))
 		return -1;
 
 	if (pack_options_allow_reuse() &&
 	    !reuse_partial_packfile_from_bitmap(
+			bitmap_git,
 			&reuse_packfile,
 			&reuse_packfile_objects,
 			&reuse_packfile_offset)) {
@@ -2942,7 +2944,7 @@ static int get_object_list_from_bitmap(struct rev_info *revs)
 		display_progress(progress_state, nr_result);
 	}
 
-	traverse_bitmap_commit_list(&add_object_entry_from_bitmap);
+	traverse_bitmap_commit_list(bitmap_git, &add_object_entry_from_bitmap);
 	return 0;
 }
 

builtin/rev-list.c

@@ -16,6 +16,7 @@
 #include "reflog-walk.h"
 #include "oidset.h"
 #include "packfile.h"
+#include "object-store.h"
 
 static const char rev_list_usage[] =
 "git rev-list [OPTION] <commit-id>... [ -- paths... ]\n"
@@ -514,8 +515,9 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 		if (revs.count && !revs.left_right && !revs.cherry_mark) {
 			uint32_t commit_count;
 			int max_count = revs.max_count;
-			if (!prepare_bitmap_walk(&revs)) {
-				count_bitmap_commit_list(&commit_count, NULL, NULL, NULL);
+			struct bitmap_index *bitmap_git;
+			if ((bitmap_git = prepare_bitmap_walk(&revs))) {
+				count_bitmap_commit_list(bitmap_git, &commit_count, NULL, NULL, NULL);
 				if (max_count >= 0 && max_count < commit_count)
 					commit_count = max_count;
 				printf("%d\n", commit_count);
@@ -523,8 +525,9 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 			}
 		} else if (revs.max_count < 0 &&
 			   revs.tag_objects && revs.tree_objects && revs.blob_objects) {
-			if (!prepare_bitmap_walk(&revs)) {
-				traverse_bitmap_commit_list(&show_object_fast);
+			struct bitmap_index *bitmap_git;
+			if ((bitmap_git = prepare_bitmap_walk(&revs))) {
+				traverse_bitmap_commit_list(bitmap_git, &show_object_fast);
 				return 0;
 			}
 		}

pack-bitmap-write.c

@@ -360,11 +360,13 @@ static int date_compare(const void *_a, const void *_b)
 
 void bitmap_writer_reuse_bitmaps(struct packing_data *to_pack)
 {
-	if (prepare_bitmap_git() < 0)
+	struct bitmap_index *bitmap_git;
+	if (!(bitmap_git = prepare_bitmap_git()))
 		return;
 
 	writer.reused = kh_init_sha1();
-	rebuild_existing_bitmaps(to_pack, writer.reused, writer.show_progress);
+	rebuild_existing_bitmaps(bitmap_git, to_pack, writer.reused,
+				 writer.show_progress);
 }
 
 static struct ewah_bitmap *find_reused_bitmap(const unsigned char *sha1)

pack-bitmap.h

@@ -34,13 +34,20 @@ typedef int (*show_reachable_fn)(
 	struct packed_git *found_pack,
 	off_t found_offset);
 
-int prepare_bitmap_git(void);
-void count_bitmap_commit_list(uint32_t *commits, uint32_t *trees, uint32_t *blobs, uint32_t *tags);
-void traverse_bitmap_commit_list(show_reachable_fn show_reachable);
+struct bitmap_index;
+
+struct bitmap_index *prepare_bitmap_git(void);
+void count_bitmap_commit_list(struct bitmap_index *, uint32_t *commits,
+			      uint32_t *trees, uint32_t *blobs, uint32_t *tags);
+void traverse_bitmap_commit_list(struct bitmap_index *,
+				 show_reachable_fn show_reachable);
 void test_bitmap_walk(struct rev_info *revs);
-int prepare_bitmap_walk(struct rev_info *revs);
-int reuse_partial_packfile_from_bitmap(struct packed_git **packfile, uint32_t *entries, off_t *up_to);
-int rebuild_existing_bitmaps(struct packing_data *mapping, khash_sha1 *reused_bitmaps, int show_progress);
+struct bitmap_index *prepare_bitmap_walk(struct rev_info *revs);
+int reuse_partial_packfile_from_bitmap(struct bitmap_index *,
+				       struct packed_git **packfile,
+				       uint32_t *entries, off_t *up_to);
+int rebuild_existing_bitmaps(struct bitmap_index *, struct packing_data *mapping,
+			     khash_sha1 *reused_bitmaps, int show_progress);
 
 void bitmap_writer_show_progress(int show);
 void bitmap_writer_set_checksum(unsigned char *sha1);