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: Stefan Beller <sbeller@google.com>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index 7b2dc3e..03e1225 100644
--- a/pack-bitmap-write.c
+++ b/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)