index: add iterator_space helper

The new helper function returns the space the iterator was created for.
It looks up the space by id and caches it in iterator struct. We need it
for space upgrade: we will use it in box_iterator_next() to update
tuples returned by iterator_next().

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal

Author: locker

src/box/index.cc

@@ -398,6 +398,7 @@ box_index_iterator(uint32_t space_id, uint32_t index_id, int type,
 		txn_rollback_stmt(txn);
 		return NULL;
 	}
+	it->space = space;
 	txn_commit_ro_stmt(txn, &svp);
 	rmean_collect(rmean_box, IPROTO_SELECT, 1);
 	return it;
@@ -461,6 +462,27 @@ iterator_create(struct iterator *it, struct index *index)
 	it->space_id = index->def->space_id;
 	it->index_id = index->def->iid;
 	it->index = index;
+	it->space = NULL;
+}
+
+/**
+ * Helper function that checks that the iterated index wasn't dropped
+ * and updates it->space and it->space_cache_version on success.
+ * Returns 0 on success, -1 on failure.
+ */
+static int
+iterator_check_space(struct iterator *it)
+{
+	struct space *space = space_by_id(it->space_id);
+	if (space == NULL)
+		return -1;
+	struct index *index = space_index(space, it->index_id);
+	if (index != it->index ||
+	    index->space_cache_version > it->space_cache_version)
+		return -1;
+	it->space_cache_version = space_cache_version;
+	it->space = space;
+	return 0;
 }
 
 static bool
@@ -470,18 +492,20 @@ iterator_is_valid(struct iterator *it)
 	if (it->space_id == 0)
 		return true;
 	if (unlikely(it->space_cache_version != space_cache_version)) {
-		struct space *space = space_by_id(it->space_id);
-		if (space == NULL)
+		if (iterator_check_space(it) != 0)
 			return false;
-		struct index *index = space_index(space, it->index_id);
-		if (index != it->index ||
-		    index->space_cache_version > it->space_cache_version)
-			return false;
-		it->space_cache_version = space_cache_version;
 	}
 	return true;
 }
 
+struct space *
+iterator_space_slow(struct iterator *it)
+{
+	if (iterator_check_space(it) != 0)
+		return NULL;
+	return it->space;
+}
+
 int
 iterator_next(struct iterator *it, struct tuple **ret)
 {

src/box/index.h

@@ -300,6 +300,11 @@ struct iterator {
 	 * state has not changed since the last lookup.
 	 */
 	struct index *index;
+	/**
+	 * Pointer to the space this iterator is for.
+	 * Don't access directly, use iterator_space().
+	 */
+	struct space *space;
 };
 
 /**
@@ -312,6 +317,24 @@ struct iterator {
 void
 iterator_create(struct iterator *it, struct index *index);
 
+/** iterator_space() slow path. */
+struct space *
+iterator_space_slow(struct iterator *it);
+
+/**
+ * Returns the space this iterator is for or NULL if the iterator is invalid
+ * (e.g. the index was dropped).
+ */
+static inline struct space *
+iterator_space(struct iterator *it)
+{
+	extern uint32_t space_cache_version;
+	if (likely(it->space != NULL &&
+		   it->space_cache_version == space_cache_version))
+		return it->space;
+	return iterator_space_slow(it);
+}
+
 /**
  * Iterate to the next tuple.
  *

src/box/memtx_engine.h

@@ -118,7 +118,7 @@ enum memtx_reserve_extents_num {
  * allocated for each iterator (except rtree index iterator that
  * is significantly bigger so has own pool).
  */
-#define MEMTX_ITERATOR_SIZE (184)
+#define MEMTX_ITERATOR_SIZE (192)
 
 struct memtx_engine {
 	struct engine base;