odb/source: generalize reprepare() callback

The `reprepare()` callback function can be used to flush caches of a
given object source and then prepare it anew. This is for example used
when a concurrent process may have written new objects. Ultimately, this
can be seen as doing two separate steps:

  1. We drop any caches.

  2. We prepare the source.

We have one callsite in git-grep(1) though that really only want to do
(2). This is done by reaching into the "files" backend directly and then
calling `odb_source_packed_prepare()`, which of course may not work with
alternate backends.

We could in theory just call `reprepare()` here, and that would likely
not have any significant downside. But this would certainly feel like a
code smell.

Instead, generalize the `reprepare()` callback to `prepare()` with a
flag that optionally instructs the backend to also flush the caches,
which allows us to drop the external `odb_source_packed_prepare()`
declaration.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/grep.c

@@ -25,12 +25,11 @@
 #include "setup.h"
 #include "submodule.h"
 #include "submodule-config.h"
-#include "object-file.h"
 #include "object-name.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "oid-array.h"
 #include "oidset.h"
-#include "packfile.h"
 #include "pager.h"
 #include "path.h"
 #include "promisor-remote.h"
@@ -1361,10 +1360,8 @@ int cmd_grep(int argc,
 			struct odb_source *source;
 
 			odb_prepare_alternates(the_repository->objects);
-			for (source = the_repository->objects->sources; source; source = source->next) {
-				struct odb_source_files *files = odb_source_files_downcast(source);
-				odb_source_packed_prepare(files->packed);
-			}
+			for (source = the_repository->objects->sources; source; source = source->next)
+				odb_source_prepare(source, 0);
 		}
 
 		start_threads(&opt);

midx.c

@@ -101,7 +101,7 @@ static int midx_read_object_offsets(const unsigned char *chunk_start,
 
 struct multi_pack_index *get_multi_pack_index(struct odb_source_packed *source)
 {
-	odb_source_packed_prepare(source);
+	odb_source_prepare(&source->base, 0);
 	return source->midx;
 }
 

odb.c

@@ -1086,7 +1086,7 @@ void odb_reprepare(struct object_database *o)
 	odb_prepare_alternates(o);
 
 	for (source = o->sources; source; source = source->next)
-		odb_source_reprepare(source);
+		odb_source_prepare(source, ODB_PREPARE_FLUSH_CACHES);
 
 	o->object_count_valid = 0;
 

odb.h

@@ -124,6 +124,14 @@ void odb_free(struct object_database *o);
  */
 void odb_close(struct object_database *o);
 
+enum odb_prepare_flags {
+	/*
+	 * Flush caches, reload alternates and then re-prepare each object
+	 * source so that new objects may become accessible.
+	 */
+	ODB_PREPARE_FLUSH_CACHES = (1 << 0),
+};
+
 /*
  * Clear caches, reload alternates and then reload object sources so that new
  * objects may become accessible.

odb/source-files.c

@@ -41,11 +41,12 @@ static void odb_source_files_close(struct odb_source *source)
 	odb_source_close(&files->packed->base);
 }
 
-static void odb_source_files_reprepare(struct odb_source *source)
+static void odb_source_files_prepare(struct odb_source *source,
+				     enum odb_prepare_flags flags)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	odb_source_reprepare(&files->loose->base);
-	odb_source_reprepare(&files->packed->base);
+	odb_source_prepare(&files->loose->base, flags);
+	odb_source_prepare(&files->packed->base, flags);
 }
 
 static int odb_source_files_read_object_info(struct odb_source *source,
@@ -273,7 +274,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 
 	files->base.free = odb_source_files_free;
 	files->base.close = odb_source_files_close;
-	files->base.reprepare = odb_source_files_reprepare;
+	files->base.prepare = odb_source_files_prepare;
 	files->base.read_object_info = odb_source_files_read_object_info;
 	files->base.read_object_stream = odb_source_files_read_object_stream;
 	files->base.for_each_object = odb_source_files_for_each_object;

odb/source-inmemory.c

@@ -325,7 +325,8 @@ static void odb_source_inmemory_close(struct odb_source *source UNUSED)
 {
 }
 
-static void odb_source_inmemory_reprepare(struct odb_source *source UNUSED)
+static void odb_source_inmemory_prepare(struct odb_source *source UNUSED,
+					enum odb_prepare_flags flags UNUSED)
 {
 }
 
@@ -365,7 +366,7 @@ struct odb_source_inmemory *odb_source_inmemory_new(struct object_database *odb)
 
 	source->base.free = odb_source_inmemory_free;
 	source->base.close = odb_source_inmemory_close;
-	source->base.reprepare = odb_source_inmemory_reprepare;
+	source->base.prepare = odb_source_inmemory_prepare;
 	source->base.read_object_info = odb_source_inmemory_read_object_info;
 	source->base.read_object_stream = odb_source_inmemory_read_object_stream;
 	source->base.for_each_object = odb_source_inmemory_for_each_object;

odb/source-loose.c

@@ -672,10 +672,12 @@ static void odb_source_loose_clear_cache(struct odb_source_loose *loose)
 	       sizeof(loose->subdir_seen));
 }
 
-static void odb_source_loose_reprepare(struct odb_source *source)
+static void odb_source_loose_prepare(struct odb_source *source,
+				     enum odb_prepare_flags flags)
 {
 	struct odb_source_loose *loose = odb_source_loose_downcast(source);
-	odb_source_loose_clear_cache(loose);
+	if (flags & ODB_PREPARE_FLUSH_CACHES)
+		odb_source_loose_clear_cache(loose);
 }
 
 static void odb_source_loose_close(struct odb_source *source UNUSED)
@@ -716,7 +718,7 @@ struct odb_source_loose *odb_source_loose_new(struct object_database *odb,
 
 	loose->base.free = odb_source_loose_free;
 	loose->base.close = odb_source_loose_close;
-	loose->base.reprepare = odb_source_loose_reprepare;
+	loose->base.prepare = odb_source_loose_prepare;
 	loose->base.read_object_info = odb_source_loose_read_object_info;
 	loose->base.read_object_stream = odb_source_loose_read_object_stream;
 	loose->base.for_each_object = odb_source_loose_for_each_object;

odb/source-packed.c

@@ -15,7 +15,7 @@ static int find_pack_entry(struct odb_source_packed *store,
 {
 	struct packfile_list_entry *l;
 
-	odb_source_packed_prepare(store);
+	odb_source_prepare(&store->base, 0);
 	if (store->midx && fill_midx_entry(store->midx, oid, e))
 		return 1;
 
@@ -47,7 +47,7 @@ static int odb_source_packed_read_object_info(struct odb_source *source,
 	 * been added since the last time we have prepared the packfile store.
 	 */
 	if (flags & OBJECT_INFO_SECOND_READ)
-		odb_source_reprepare(source);
+		odb_source_prepare(source, ODB_PREPARE_FLUSH_CACHES);
 
 	if (!find_pack_entry(packed, oid, &e))
 		return 1;
@@ -668,27 +668,25 @@ static int sort_pack(const struct packfile_list_entry *a,
 	return -1;
 }
 
-void odb_source_packed_prepare(struct odb_source_packed *source)
+static void odb_source_packed_prepare(struct odb_source *source,
+				      enum odb_prepare_flags flags)
 {
-	if (source->initialized)
+	struct odb_source_packed *packed = odb_source_packed_downcast(source);
+
+	if (flags & ODB_PREPARE_FLUSH_CACHES)
+		packed->initialized = false;
+	if (packed->initialized)
 		return;
 
-	prepare_multi_pack_index_one(source);
-	prepare_packed_git_one(source);
+	prepare_multi_pack_index_one(packed);
+	prepare_packed_git_one(packed);
 
-	sort_packs(&source->packs.head, sort_pack);
-	for (struct packfile_list_entry *e = source->packs.head; e; e = e->next)
+	sort_packs(&packed->packs.head, sort_pack);
+	for (struct packfile_list_entry *e = packed->packs.head; e; e = e->next)
 		if (!e->next)
-			source->packs.tail = e;
+			packed->packs.tail = e;
 
-	source->initialized = true;
-}
-
-static void odb_source_packed_reprepare(struct odb_source *source)
-{
-	struct odb_source_packed *packed = odb_source_packed_downcast(source);
-	packed->initialized = false;
-	odb_source_packed_prepare(packed);
+	packed->initialized = true;
 }
 
 static void odb_source_packed_reparent(const char *name UNUSED,
@@ -744,7 +742,7 @@ struct odb_source_packed *odb_source_packed_new(struct object_database *odb,
 
 	packed->base.free = odb_source_packed_free;
 	packed->base.close = odb_source_packed_close;
-	packed->base.reprepare = odb_source_packed_reprepare;
+	packed->base.prepare = odb_source_packed_prepare;
 	packed->base.read_object_info = odb_source_packed_read_object_info;
 	packed->base.read_object_stream = odb_source_packed_read_object_stream;
 	packed->base.for_each_object = odb_source_packed_for_each_object;

odb/source-packed.h

@@ -82,13 +82,4 @@ static inline struct odb_source_packed *odb_source_packed_downcast(struct odb_so
 	return container_of(source, struct odb_source_packed, base);
 }
 
-/*
- * Prepare the source by loading packfiles and multi-pack indices for
- * all alternates. This becomes a no-op if the source is already prepared.
- *
- * It shouldn't typically be necessary to call this function directly, as
- * functions that access the source know to prepare it.
- */
-void odb_source_packed_prepare(struct odb_source_packed *source);
-
 #endif

odb/source.h

@@ -83,11 +83,12 @@ struct odb_source {
 	void (*close)(struct odb_source *source);
 
 	/*
-	 * This callback is expected to clear underlying caches of the object
-	 * database source. The function is called when the repository has for
-	 * example just been repacked so that new objects will become visible.
+	 * This callback is expected to prepare the source so that it becomes
+	 * ready for use. It optionally clears underlying caches of the object
+	 * database source.
 	 */
-	void (*reprepare)(struct odb_source *source);
+	void (*prepare)(struct odb_source *source,
+			enum odb_prepare_flags flags);
 
 	/*
 	 * This callback is expected to read object information from the object
@@ -308,13 +309,14 @@ static inline void odb_source_close(struct odb_source *source)
 }
 
 /*
- * Reprepare the object database source and clear any caches. Depending on the
+ * Prepare the object database source and clear any caches. Depending on the
  * backend used this may have the effect that concurrently-written objects
  * become visible.
  */
-static inline void odb_source_reprepare(struct odb_source *source)
+static inline void odb_source_prepare(struct odb_source *source,
+				      enum odb_prepare_flags flags)
 {
-	source->reprepare(source);
+	source->prepare(source, flags);
 }
 
 /*