pack-bitmap: avoid use of static `bitmap_writer`

The pack-bitmap machinery uses a structure called 'bitmap_writer' to
collect the data necessary to write out .bitmap files. Since its
introduction in 7cc8f971085 (pack-objects: implement bitmap writing,
2013-12-21), there has been a single static bitmap_writer structure,
which is responsible for all bitmap writing-related operations.

In practice, this is OK, since we are only ever writing a single .bitmap
file in a single process (e.g., `git multi-pack-index write --bitmap`,
`git pack-objects --write-bitmap-index`, `git repack -b`, etc.).

However, having a single static variable makes issues like data
ownership unclear, when to free variables, what has/hasn't been
initialized unclear.

Refactor this code to be written in terms of a given bitmap_writer
structure instead of relying on a static global.

Note that this exposes the structure definition of the bitmap_writer at
the pack-bitmap.h level. We could work around this by, e.g., forcing
callers to declare their writers as:

    struct bitmap_writer *writer;
    bitmap_writer_init(&bitmap_writer);

and then declaring `bitmap_writer_init()` as taking in a double-pointer
like so:

    void bitmap_writer_init(struct bitmap_writer **writer);

which would avoid us having to expose the definition of the structure
itself. This patch takes a different approach, since future patches
(like for the ongoing pseudo-merge bitmaps work) will want to modify the
innards of this structure (in the previous example, via pseudo-merge.c).

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 31 insertions, 7 deletions

diff --git a/pack-bitmap.h b/pack-bitmap.h
index c7dea13217..5a1890a2c5 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -97,9 +97,29 @@ int bitmap_has_oid_in_uninteresting(struct bitmap_index *, const struct object_i
 
 off_t get_disk_usage_from_bitmap(struct bitmap_index *, struct rev_info *);
 
-void bitmap_writer_show_progress(int show);
-void bitmap_writer_set_checksum(const unsigned char *sha1);
-void bitmap_writer_build_type_index(struct packing_data *to_pack,
+struct bitmap_writer {
+	struct ewah_bitmap *commits;
+	struct ewah_bitmap *trees;
+	struct ewah_bitmap *blobs;
+	struct ewah_bitmap *tags;
+
+	kh_oid_map_t *bitmaps;
+	struct packing_data *to_pack;
+
+	struct bitmapped_commit *selected;
+	unsigned int selected_nr, selected_alloc;
+
+	struct progress *progress;
+	int show_progress;
+	unsigned char pack_checksum[GIT_MAX_RAWSZ];
+};
+
+void bitmap_writer_init(struct bitmap_writer *writer);
+void bitmap_writer_show_progress(struct bitmap_writer *writer, int show);
+void bitmap_writer_set_checksum(struct bitmap_writer *writer,
+				const unsigned char *sha1);
+void bitmap_writer_build_type_index(struct bitmap_writer *writer,
+				    struct packing_data *to_pack,
 				    struct pack_idx_entry **index,
 				    uint32_t index_nr);
 uint32_t *create_bitmap_mapping(struct bitmap_index *bitmap_git,
@@ -109,10 +129,14 @@ int rebuild_bitmap(const uint32_t *reposition,
 		   struct bitmap *dest);
 struct ewah_bitmap *bitmap_for_commit(struct bitmap_index *bitmap_git,
 				      struct commit *commit);
-void bitmap_writer_select_commits(struct commit **indexed_commits,
-		unsigned int indexed_commits_nr, int max_bitmaps);
-int bitmap_writer_build(struct packing_data *to_pack);
-void bitmap_writer_finish(struct pack_idx_entry **index,
+void bitmap_writer_select_commits(struct bitmap_writer *writer,
+				  struct commit **indexed_commits,
+				  unsigned int indexed_commits_nr,
+				  int max_bitmaps);
+int bitmap_writer_build(struct bitmap_writer *writer,
+			struct packing_data *to_pack);
+void bitmap_writer_finish(struct bitmap_writer *writer,
+			  struct pack_idx_entry **index,
 			  uint32_t index_nr,
 			  const char *filename,
 			  uint16_t options);