[RFC/WIP PATCH] object store classification

[Stefan Beller <sbeller@google.com>]

This continues the efforts of bw/repo-object, making our code base
more object oriented by adding the object store to the the repository struct.

Long term goal of the series that would evolve from this discussion:
* Easier to implement submodule features as it can be in the same process.

Short term goal:
* get rid of 'add_submodule_odb' in submodule.c
  When fetching or pushing we need to determine if a submodule needs processing
  by finding out if certain commits are present.  To do this we add the submodule
  objects as an alternate object database and do the processing in the same
  process. In case of multiple submodules, this would pollute the object store
  hence being slower and increasing memory usage, too.

This patch only changes the object store code to be object oriented based
on the repository struct.

To go for the short term goal we'd need to convert a few more places, mostly
all the construction (blob.c, tree.c, commit.c)

This is marked RFC as I'd want to gather feedback if the approach, presented
in the header files is sound.

Thanks!

Signed-off-by: Stefan Beller <sbeller@google.com>
---

  Peff, this area of the code seems performance sensitive for a variety of
  use cases, specifically yours. So I cc'd you here. :)

 object.c     | 77 +++++++++++++++++++++++++++++++++++-------------------------
 object.h     | 51 ++++++++++++++++++++++++++++++++--------
 repository.h |  6 +++++
 3 files changed, 92 insertions(+), 42 deletions(-)

diff --git a/object.c b/object.c
index 06ba3a11d8..b5ec0bb2f9 100644
--- a/object.c
+++ b/object.c
@@ -5,17 +5,15 @@
 #include "commit.h"
 #include "tag.h"
 
-static struct object **obj_hash;
-static int nr_objs, obj_hash_size;
-
-unsigned int get_max_object_index(void)
+unsigned int object_store_get_max_index(struct repository *r)
 {
-	return obj_hash_size;
+	return r->objects.obj_hash_size;
 }
 
-struct object *get_indexed_object(unsigned int idx)
+struct object *object_store_get_indexed(struct repository *r,
+					unsigned int idx)
 {
-	return obj_hash[idx];
+	return r->objects.obj_hash[idx];
 }
 
 static const char *object_type_strings[] = {
@@ -82,11 +80,15 @@ static void insert_obj_hash(struct object *obj, struct object **hash, unsigned i
  * Look up the record for the given sha1 in the hash map stored in
  * obj_hash.  Return NULL if it was not found.
  */
-struct object *lookup_object(const unsigned char *sha1)
+struct object *object_store_lookup(struct repository *r,
+				   const unsigned char *sha1)
 {
 	unsigned int i, first;
 	struct object *obj;
 
+	struct object **obj_hash = r->objects.obj_hash;
+	int obj_hash_size = r->objects.obj_hash_size;
+
 	if (!obj_hash)
 		return NULL;
 
@@ -114,29 +116,31 @@ struct object *lookup_object(const unsigned char *sha1)
  * power of 2 (but at least 32).  Copy the existing values to the new
  * hash map.
  */
-static void grow_object_hash(void)
+static void grow_object_hash(struct repository *r)
 {
 	int i;
 	/*
 	 * Note that this size must always be power-of-2 to match hash_obj
 	 * above.
 	 */
-	int new_hash_size = obj_hash_size < 32 ? 32 : 2 * obj_hash_size;
+	int new_hash_size = r->objects.obj_hash_size < 32 ?
+			32 : 2 * r->objects.obj_hash_size;
 	struct object **new_hash;
 
 	new_hash = xcalloc(new_hash_size, sizeof(struct object *));
-	for (i = 0; i < obj_hash_size; i++) {
-		struct object *obj = obj_hash[i];
+	for (i = 0; i < r->objects.obj_hash_size; i++) {
+		struct object *obj = r->objects.obj_hash[i];
 		if (!obj)
 			continue;
 		insert_obj_hash(obj, new_hash, new_hash_size);
 	}
-	free(obj_hash);
-	obj_hash = new_hash;
-	obj_hash_size = new_hash_size;
+	free(r->objects.obj_hash);
+	r->objects.obj_hash = new_hash;
+	r->objects.obj_hash_size = new_hash_size;
 }
 
-void *create_object(const unsigned char *sha1, void *o)
+void *object_store_create(struct repository *r,
+			  const unsigned char *sha1, void *o)
 {
 	struct object *obj = o;
 
@@ -145,15 +149,17 @@ void *create_object(const unsigned char *sha1, void *o)
 	obj->flags = 0;
 	hashcpy(obj->oid.hash, sha1);
 
-	if (obj_hash_size - 1 <= nr_objs * 2)
-		grow_object_hash();
+	if (r->objects.obj_hash_size - 1 <= r->objects.nr_objs * 2)
+		grow_object_hash(r);
 
-	insert_obj_hash(obj, obj_hash, obj_hash_size);
-	nr_objs++;
+	insert_obj_hash(obj, r->objects.obj_hash, r->objects.obj_hash_size);
+	r->objects.nr_objs++;
 	return obj;
 }
 
-void *object_as_type(struct object *obj, enum object_type type, int quiet)
+void *object_as_type(struct object *obj,
+		     enum object_type type,
+		     int quiet)
 {
 	if (obj->type == type)
 		return obj;
@@ -172,15 +178,20 @@ void *object_as_type(struct object *obj, enum object_type type, int quiet)
 	}
 }
 
-struct object *lookup_unknown_object(const unsigned char *sha1)
+struct object *object_store_lookup_unknown_object(struct repository *r,
+						  const unsigned char *sha1)
 {
-	struct object *obj = lookup_object(sha1);
+	struct object *obj = object_store_lookup(r, sha1);
 	if (!obj)
-		obj = create_object(sha1, alloc_object_node());
+		obj = object_store_create(r, sha1, alloc_object_node());
 	return obj;
 }
 
-struct object *parse_object_buffer(const struct object_id *oid, enum object_type type, unsigned long size, void *buffer, int *eaten_p)
+struct object *object_store_parse_object_buffer(struct repository *r,
+						const struct object_id *oid,
+						enum object_type type,
+						unsigned long size,
+						void *buffer, int *eaten_p)
 {
 	struct object *obj;
 	*eaten_p = 0;
@@ -230,17 +241,19 @@ struct object *parse_object_buffer(const struct object_id *oid, enum object_type
 	return obj;
 }
 
-struct object *parse_object_or_die(const struct object_id *oid,
-				   const char *name)
+struct object *object_store_parse_object_or_die(struct repository *r,
+						const struct object_id *oid,
+						const char *name)
 {
-	struct object *o = parse_object(oid);
+	struct object *o = object_store_parse_object(r, oid);
 	if (o)
 		return o;
 
 	die(_("unable to parse object: %s"), name ? name : oid_to_hex(oid));
 }
 
-struct object *parse_object(const struct object_id *oid)
+struct object *object_store_parse_object(struct repository *r,
+					 const struct object_id *oid)
 {
 	unsigned long size;
 	enum object_type type;
@@ -413,12 +426,12 @@ void object_array_remove_duplicates(struct object_array *array)
 	}
 }
 
-void clear_object_flags(unsigned flags)
+void object_store_clear_object_flags(struct repository *r, unsigned flags)
 {
 	int i;
 
-	for (i=0; i < obj_hash_size; i++) {
-		struct object *obj = obj_hash[i];
+	for (i = 0; i < r->objects.obj_hash_size; i++) {
+		struct object *obj = r->objects.obj_hash[i];
 		if (obj)
 			obj->flags &= ~flags;
 	}
diff --git a/object.h b/object.h
index 33e5cc9943..1b2ab8ee88 100644
--- a/object.h
+++ b/object.h
@@ -1,6 +1,8 @@
 #ifndef OBJECT_H
 #define OBJECT_H
 
+#include "repository.h"
+
 struct object_list {
 	struct object *item;
 	struct object_list *next;
@@ -59,12 +61,15 @@ extern int type_from_string_gently(const char *str, ssize_t, int gentle);
 /*
  * Return the current number of buckets in the object hashmap.
  */
-extern unsigned int get_max_object_index(void);
+extern unsigned int object_store_get_max_index(struct repository *r);
+#define get_max_object_index() object_store_get_max_index(the_repository)
 
 /*
  * Return the object from the specified bucket in the object hashmap.
  */
-extern struct object *get_indexed_object(unsigned int);
+extern struct object *object_store_get_indexed(struct repository *r,
+					       unsigned int);
+#define get_indexed_object(i) object_store_get_indexed(the_repository, i)
 
 /*
  * This can be used to see if we have heard of the object before, but
@@ -78,34 +83,59 @@ extern struct object *get_indexed_object(unsigned int);
  * half-initialised objects, the caller is expected to initialize them
  * by calling parse_object() on them.
  */
-struct object *lookup_object(const unsigned char *sha1);
+extern struct object *object_store_lookup(struct repository *r,
+					  const unsigned char *sha1);
+#define lookup_object(hash) object_store_lookup(the_repository, hash)
 
-extern void *create_object(const unsigned char *sha1, void *obj);
+extern void *object_store_create(struct repository *r,
+				 const unsigned char *sha1,
+				 void *obj);
+#define create_object(sha1, obj) object_store_create(the_repository, sha1, obj)
 
-void *object_as_type(struct object *obj, enum object_type type, int quiet);
+extern void *object_as_type(struct object *obj,
+			    enum object_type type,
+			    int quiet);
 
 /*
  * Returns the object, having parsed it to find out what it is.
  *
  * Returns NULL if the object is missing or corrupt.
  */
-struct object *parse_object(const struct object_id *oid);
+extern struct object *object_store_parse_object(struct repository *r,
+						const struct object_id *oid);
+#define parse_object(sha1) \
+	object_store_parse_object(the_repository, sha1)
 
 /*
  * Like parse_object, but will die() instead of returning NULL. If the
  * "name" parameter is not NULL, it is included in the error message
  * (otherwise, the hex object ID is given).
  */
-struct object *parse_object_or_die(const struct object_id *oid, const char *name);
+extern struct object *object_store_parse_object_or_die(struct repository *r,
+						       const struct object_id *oid,
+						       const char *name);
+#define parse_object_or_die(oid, name) \
+	object_store_parse_object_or_die(the_repository, oid, name)
 
 /* Given the result of read_sha1_file(), returns the object after
  * parsing it.  eaten_p indicates if the object has a borrowed copy
  * of buffer and the caller should not free() it.
  */
-struct object *parse_object_buffer(const struct object_id *oid, enum object_type type, unsigned long size, void *buffer, int *eaten_p);
+struct object *object_store_parse_object_buffer(struct repository *r,
+						const struct object_id *oid,
+						enum object_type type,
+						unsigned long size,
+						void *buffer,
+						int *eaten_p);
+#define parse_object_buffer(oid, type, size, buffer, eaten_p) \
+	object_store_parse_object_buffer(the_repository, oid, type, \
+					 size, buffer, eaten_p)
 
 /** Returns the object, with potentially excess memory allocated. **/
-struct object *lookup_unknown_object(const unsigned  char *sha1);
+struct object *object_store_lookup_unknown_object(struct repository *r,
+						  const unsigned char *sha1);
+#define lookup_unknown_object(sha1) \
+	object_store_lookup_unknown_object(the_repository, sha1)
 
 struct object_list *object_list_insert(struct object *item,
 				       struct object_list **list_p);
@@ -138,6 +168,7 @@ void object_array_remove_duplicates(struct object_array *array);
  */
 void object_array_clear(struct object_array *array);
 
-void clear_object_flags(unsigned flags);
+extern void object_store_clear_object_flags(struct repository *r, unsigned flags);
+#define clear_object_flags(flags) object_store_clear_object_flags(the_repository, flags);
 
 #endif /* OBJECT_H */
diff --git a/repository.h b/repository.h
index 417787f3ef..aeb50a19bc 100644
--- a/repository.h
+++ b/repository.h
@@ -1,6 +1,8 @@
 #ifndef REPOSITORY_H
 #define REPOSITORY_H
 
+#include "object.h"
+
 struct config_set;
 struct index_state;
 struct submodule_cache;
@@ -24,6 +26,10 @@ struct repository {
 	 * Cannot be NULL after initialization.
 	 */
 	char *objectdir;
+	struct object_store {
+		struct object **obj_hash;
+		int nr_objs, obj_hash_size;
+	} objects;
 
 	/*
 	 * Path to the repository's graft file.
-- 
2.13.2.559.g3a0a3146e4