odb: add transaction interface

Transactions are managed via the {begin,end}_odb_transaction() function
in the object-file subsystem and its implementation is specific to the
files object source. Introduce odb_transaction_{begin,commit}() in the
odb subsystem to provide an eventual object source agnostic means to
manage transactions.

Update call sites to instead manage transactions through the odb
subsystem. Also rename {begin,end}_odb_transaction() functions to
object_file_transaction_{begin,commit}() to clarify the object source it
supports.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/add.c

@@ -15,6 +15,7 @@
 #include "pathspec.h"
 #include "run-command.h"
 #include "object-file.h"
+#include "odb.h"
 #include "parse-options.h"
 #include "path.h"
 #include "preload-index.h"
@@ -575,7 +576,7 @@ int cmd_add(int argc,
 		string_list_clear(&only_match_skip_worktree, 0);
 	}
 
-	transaction = begin_odb_transaction(repo->objects);
+	transaction = odb_transaction_begin(repo->objects);
 
 	ps_matched = xcalloc(pathspec.nr, 1);
 	if (add_renormalize)
@@ -594,7 +595,7 @@ int cmd_add(int argc,
 
 	if (chmod_arg && pathspec.nr)
 		exit_status |= chmod_pathspec(repo, &pathspec, chmod_arg[0], show_only);
-	end_odb_transaction(transaction);
+	odb_transaction_commit(transaction);
 
 finish:
 	if (write_locked_index(repo->index, &lock_file,

builtin/unpack-objects.c

@@ -599,12 +599,12 @@ static void unpack_all(void)
 		progress = start_progress(the_repository,
 					  _("Unpacking objects"), nr_objects);
 	CALLOC_ARRAY(obj_list, nr_objects);
-	transaction = begin_odb_transaction(the_repository->objects);
+	transaction = odb_transaction_begin(the_repository->objects);
 	for (i = 0; i < nr_objects; i++) {
 		unpack_one(i);
 		display_progress(progress, i + 1);
 	}
-	end_odb_transaction(transaction);
+	odb_transaction_commit(transaction);
 	stop_progress(&progress);
 
 	if (delta_list)

builtin/update-index.c

@@ -18,6 +18,7 @@
 #include "cache-tree.h"
 #include "tree-walk.h"
 #include "object-file.h"
+#include "odb.h"
 #include "refs.h"
 #include "resolve-undo.h"
 #include "parse-options.h"
@@ -1122,7 +1123,7 @@ int cmd_update_index(int argc,
 	 * Allow the object layer to optimize adding multiple objects in
 	 * a batch.
 	 */
-	transaction = begin_odb_transaction(the_repository->objects);
+	transaction = odb_transaction_begin(the_repository->objects);
 	while (ctx.argc) {
 		if (parseopt_state != PARSE_OPT_DONE)
 			parseopt_state = parse_options_step(&ctx, options,
@@ -1152,7 +1153,7 @@ int cmd_update_index(int argc,
 			 * a transaction.
 			 */
 			if (transaction && verbose) {
-				end_odb_transaction(transaction);
+				odb_transaction_commit(transaction);
 				transaction = NULL;
 			}
 
@@ -1220,7 +1221,7 @@ int cmd_update_index(int argc,
 	/*
 	 * By now we have added all of the new objects
 	 */
-	end_odb_transaction(transaction);
+	odb_transaction_commit(transaction);
 
 	if (split_index > 0) {
 		if (repo_config_get_split_index(the_repository) == 0)

cache-tree.c

@@ -489,10 +489,10 @@ int cache_tree_update(struct index_state *istate, int flags)
 
 	trace_performance_enter();
 	trace2_region_enter("cache_tree", "update", the_repository);
-	transaction = begin_odb_transaction(the_repository->objects);
+	transaction = odb_transaction_begin(the_repository->objects);
 	i = update_one(istate->cache_tree, istate->cache, istate->cache_nr,
 		       "", 0, &skip, flags);
-	end_odb_transaction(transaction);
+	odb_transaction_commit(transaction);
 	trace2_region_leave("cache_tree", "update", the_repository);
 	trace_performance_leave("cache_tree_update");
 	if (i < 0)

object-file.c

@@ -691,7 +691,7 @@ static void prepare_loose_object_transaction(struct odb_transaction *transaction
 	 * We lazily create the temporary object directory
 	 * the first time an object might be added, since
 	 * callers may not know whether any objects will be
-	 * added at the time they call begin_odb_transaction.
+	 * added at the time they call object_file_transaction_begin.
 	 */
 	if (!transaction || transaction->objdir)
 		return;
@@ -1622,12 +1622,12 @@ int index_fd(struct index_state *istate, struct object_id *oid,
 	} else {
 		struct odb_transaction *transaction;
 
-		transaction = begin_odb_transaction(the_repository->objects);
+		transaction = odb_transaction_begin(the_repository->objects);
 		ret = index_blob_packfile_transaction(the_repository->objects->transaction,
 						      oid, fd,
 						      xsize_t(st->st_size),
 						      path, flags);
-		end_odb_transaction(transaction);
+		odb_transaction_commit(transaction);
 	}
 
 	close(fd);
@@ -1967,8 +1967,10 @@ out:
 	return ret;
 }
 
-struct odb_transaction *begin_odb_transaction(struct object_database *odb)
+struct odb_transaction *object_file_transaction_begin(struct odb_source *source)
 {
+	struct object_database *odb = source->odb;
+
 	if (odb->transaction)
 		return NULL;
 
@@ -1978,7 +1980,7 @@ struct odb_transaction *begin_odb_transaction(struct object_database *odb)
 	return odb->transaction;
 }
 
-void end_odb_transaction(struct odb_transaction *transaction)
+void object_file_transaction_commit(struct odb_transaction *transaction)
 {
 	if (!transaction)
 		return;

object-file.h

@@ -222,16 +222,16 @@ struct odb_transaction;
 
 /*
  * Tell the object database to optimize for adding
- * multiple objects. end_odb_transaction must be called
+ * multiple objects. object_file_transaction_commit must be called
  * to make new objects visible. If a transaction is already
  * pending, NULL is returned.
  */
-struct odb_transaction *begin_odb_transaction(struct object_database *odb);
+struct odb_transaction *object_file_transaction_begin(struct odb_source *source);
 
 /*
  * Tell the object database to make any objects from the
  * current transaction visible.
  */
-void end_odb_transaction(struct odb_transaction *transaction);
+void object_file_transaction_commit(struct odb_transaction *transaction);
 
 #endif /* OBJECT_FILE_H */

odb.c

@@ -1051,3 +1051,13 @@ void odb_clear(struct object_database *o)
 	hashmap_clear(&o->pack_map);
 	string_list_clear(&o->submodule_source_paths, 0);
 }
+
+struct odb_transaction *odb_transaction_begin(struct object_database *odb)
+{
+	return object_file_transaction_begin(odb->sources);
+}
+
+void odb_transaction_commit(struct odb_transaction *transaction)
+{
+	object_file_transaction_commit(transaction);
+}

odb.h

@@ -185,6 +185,19 @@ struct object_database {
 struct object_database *odb_new(struct repository *repo);
 void odb_clear(struct object_database *o);
 
+/*
+ * Starts an ODB transaction. Subsequent objects are written to the transaction
+ * and not committed until odb_transaction_commit() is invoked on the
+ * transaction. If the ODB already has a pending transaction, NULL is returned.
+ */
+struct odb_transaction *odb_transaction_begin(struct object_database *odb);
+
+/*
+ * Commits an ODB transaction making the written objects visible. If the
+ * specified transaction is NULL, the function is a no-op.
+ */
+void odb_transaction_commit(struct odb_transaction *transaction);
+
 /*
  * Find source by its object directory path. Dies in case the source couldn't
  * be found.

read-cache.c

@@ -3972,9 +3972,9 @@ int add_files_to_cache(struct repository *repo, const char *prefix,
 	 * This function is invoked from commands other than 'add', which
 	 * may not have their own transaction active.
 	 */
-	transaction = begin_odb_transaction(repo->objects);
+	transaction = odb_transaction_begin(repo->objects);
 	run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);
-	end_odb_transaction(transaction);
+	odb_transaction_commit(transaction);
 
 	release_revisions(&rev);
 	return !!data.add_errors;