unpack-trees: refactor prefetching code

Refactor the prefetching code in unpack-trees.c into its own function,
because it will be used elsewhere in a subsequent commit.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -410,6 +410,15 @@ struct cache_entry *dup_cache_entry(const struct cache_entry *ce, struct index_s
  */
 void validate_cache_entries(const struct index_state *istate);
 
+/*
+ * Bulk prefetch all missing cache entries that are not GITLINKs and that match
+ * the given predicate. This function should only be called if
+ * has_promisor_remote() returns true.
+ */
+typedef int (*must_prefetch_predicate)(const struct cache_entry *);
+void prefetch_cache_entries(const struct index_state *istate,
+			    must_prefetch_predicate must_prefetch);
+
 #ifdef USE_THE_INDEX_COMPATIBILITY_MACROS
 extern struct index_state the_index;
 

read-cache.c

@@ -27,6 +27,7 @@
 #include "progress.h"
 #include "sparse-index.h"
 #include "csum-file.h"
+#include "promisor-remote.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -3657,3 +3658,25 @@ static void write_ieot_extension(struct strbuf *sb, struct index_entry_offset_ta
 		strbuf_add(sb, &buffer, sizeof(uint32_t));
 	}
 }
+
+void prefetch_cache_entries(const struct index_state *istate,
+			    must_prefetch_predicate must_prefetch)
+{
+	int i;
+	struct oid_array to_fetch = OID_ARRAY_INIT;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+
+		if (S_ISGITLINK(ce->ce_mode) || !must_prefetch(ce))
+			continue;
+		if (!oid_object_info_extended(the_repository, &ce->oid,
+					      NULL,
+					      OBJECT_INFO_FOR_PREFETCH))
+			continue;
+		oid_array_append(&to_fetch, &ce->oid);
+	}
+	promisor_remote_get_direct(the_repository,
+				   to_fetch.oid, to_fetch.nr);
+	oid_array_clear(&to_fetch);
+}

unpack-trees.c

@@ -392,6 +392,11 @@ static void report_collided_checkout(struct index_state *index)
 	string_list_clear(&list, 0);
 }
 
+static int must_checkout(const struct cache_entry *ce)
+{
+	return ce->ce_flags & CE_UPDATE;
+}
+
 static int check_updates(struct unpack_trees_options *o,
 			 struct index_state *index)
 {
@@ -442,28 +447,12 @@ static int check_updates(struct unpack_trees_options *o,
 	if (should_update_submodules())
 		load_gitmodules_file(index, &state);
 
-	if (has_promisor_remote()) {
+	if (has_promisor_remote())
 		/*
 		 * Prefetch the objects that are to be checked out in the loop
 		 * below.
 		 */
-		struct oid_array to_fetch = OID_ARRAY_INIT;
-		for (i = 0; i < index->cache_nr; i++) {
-			struct cache_entry *ce = index->cache[i];
-
-			if (!(ce->ce_flags & CE_UPDATE) ||
-			    S_ISGITLINK(ce->ce_mode))
-				continue;
-			if (!oid_object_info_extended(the_repository, &ce->oid,
-						      NULL,
-						      OBJECT_INFO_FOR_PREFETCH))
-				continue;
-			oid_array_append(&to_fetch, &ce->oid);
-		}
-		promisor_remote_get_direct(the_repository,
-					   to_fetch.oid, to_fetch.nr);
-		oid_array_clear(&to_fetch);
-	}
+		prefetch_cache_entries(index, must_checkout);
 
 	get_parallel_checkout_configs(&pc_workers, &pc_threshold);
 
@@ -473,7 +462,7 @@ static int check_updates(struct unpack_trees_options *o,
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
-		if (ce->ce_flags & CE_UPDATE) {
+		if (must_checkout(ce)) {
 			size_t last_pc_queue_size = pc_queue_size();
 
 			if (ce->ce_flags & CE_WT_REMOVE)