read_view: don't create tuple format when read view is opened

It's incorrect to create a tuple format when a read view is created,
because the tuple format registry isn't MT-safe so accessing a tuple
format created in the main thread from another thread by id (for
tuple_format(tuple)) may not work as expected. To address this issue,
we'll introduce a thread-local tuple format-registry. As a preparation
for this, let's create the tuple format when a read view is activated
by the thread that's going to use it (see the EE repository) while on
read view creation we now create only a field definition array necessary
to construct the format.

Needed for https://github.com/tarantool/tarantool-ee/issues/247

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

src/box/read_view.c

@@ -13,6 +13,7 @@
 
 #include "engine.h"
 #include "fiber.h"
+#include "field_def.h"
 #include "index.h"
 #include "salad/grp_alloc.h"
 #include "small/rlist.h"
@@ -53,6 +54,9 @@ read_view_opts_create(struct read_view_opts *opts)
 static void
 space_read_view_delete(struct space_read_view *space_rv)
 {
+	assert(space_rv->format == NULL);
+	if (space_rv->field_count > 0)
+		field_def_array_delete(space_rv->fields, space_rv->field_count);
 	for (uint32_t i = 0; i <= space_rv->index_id_max; i++) {
 		struct index_read_view *index_rv = space_rv->index_map[i];
 		if (index_rv != NULL) {
@@ -62,7 +66,6 @@ space_read_view_delete(struct space_read_view *space_rv)
 	}
 	if (space_rv->upgrade != NULL)
 		space_upgrade_read_view_delete(space_rv->upgrade);
-	tuple_format_unref(space_rv->format);
 	TRASH(space_rv);
 	free(space_rv);
 }
@@ -70,29 +73,6 @@ space_read_view_delete(struct space_read_view *space_rv)
 static struct space_read_view *
 space_read_view_new(struct space *space, const struct read_view_opts *opts)
 {
-	struct tuple_format *format = tuple_format_runtime;
-	if (opts->needs_field_names) {
-		/**
-		 * Sic: Even though a tuple dictionary has a reference counter,
-		 * we can't reuse the tuple dictionary used by the space tuple
-		 * format, because it may change when the space is altered, see
-		 * tuple_dictionary_swap.
-		 */
-		struct tuple_dictionary *dict = tuple_dictionary_new(
-			space->def->fields, space->def->field_count);
-		if (dict == NULL)
-			return NULL;
-		format = runtime_tuple_format_new(dict);
-		tuple_dictionary_unref(dict);
-		if (format == NULL)
-			return NULL;
-	}
-	struct space_upgrade_read_view *upgrade = NULL;
-	if (opts->needs_space_upgrade && space->upgrade != NULL) {
-		upgrade = space_upgrade_read_view_new(space->upgrade);
-		assert(upgrade != NULL);
-	}
-
 	struct space_read_view *space_rv;
 	size_t index_map_size = sizeof(*space_rv->index_map) *
 				(space->index_id_max + 1);
@@ -108,9 +88,22 @@ space_read_view_new(struct space *space, const struct read_view_opts *opts)
 
 	space_rv->id = space_id(space);
 	space_rv->group_id = space_group_id(space);
-	space_rv->format = format;
-	tuple_format_ref(format);
-	space_rv->upgrade = upgrade;
+	if (opts->needs_field_names && space->def->field_count > 0) {
+		space_rv->fields = field_def_array_dup(space->def->fields,
+						       space->def->field_count);
+		assert(space_rv->fields != NULL);
+		space_rv->field_count = space->def->field_count;
+	} else {
+		space_rv->fields = NULL;
+		space_rv->field_count = 0;
+	}
+	space_rv->format = NULL;
+	if (opts->needs_space_upgrade && space->upgrade != NULL) {
+		space_rv->upgrade = space_upgrade_read_view_new(space->upgrade);
+		assert(space_rv->upgrade != NULL);
+	} else {
+		space_rv->upgrade = NULL;
+	}
 	space_rv->index_id_max = space->index_id_max;
 	memset(space_rv->index_map, 0, index_map_size);
 	for (uint32_t i = 0; i <= space->index_id_max; i++) {

src/box/read_view.h

@@ -16,10 +16,12 @@ extern "C" {
 #endif /* defined(__cplusplus) */
 
 struct cord;
+struct field_def;
 struct index;
 struct index_read_view;
 struct space;
 struct space_upgrade_read_view;
+struct tuple_format;
 
 /** Read view of a space. */
 struct space_read_view {
@@ -31,6 +33,14 @@ struct space_read_view {
 	uint32_t id;
 	/** Space name. */
 	char *name;
+	/**
+	 * Tuple field definition array used by this space. Allocated only if
+	 * read_view_opts::needs_field_names is set, otherwise set to NULL.
+	 * Used for creation of space_read_view::format.
+	 */
+	struct field_def *fields;
+	/** Number of entries in the fields array. */
+	uint32_t field_count;
 	/**
 	 * Runtime tuple format needed to access tuple field names by name.
 	 * Referenced (ref counter incremented).