Embedded list interface

Provide a common implementation of embedded singly-linked and
doubly-linked lists.  "Embedded" in the sense that the nodes'
next/previous pointers exist within some larger struct; this design
choice reduces memory allocation overhead.

Most of the implementation uses inlineable functions (where supported),
for performance.

Some existing uses of both types of lists have been converted to the new
code, for demonstration purposes.  Other uses can (and probably will) be
converted in the future.  Since dllist.c is unused after this conversion,
it has been removed.

Author: Andres Freund
Some tweaks by me
Reviewed by Tom Lane, Peter Geoghegan

2 files changed, 767 insertions, 85 deletions

diff --git a/src/include/lib/dllist.h b/src/include/lib/dllist.h
deleted file mode 100644
index 25ed64c7c4e..00000000000
--- a/src/include/lib/dllist.h
+++ /dev/null
@@ -1,85 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * dllist.h
- *		simple doubly linked list primitives
- *		the elements of the list are void* so the lists can contain anything
- *		Dlelem can only be in one list at a time
- *
- *
- *	 Here's a small example of how to use Dllists:
- *
- *	 Dllist *lst;
- *	 Dlelem *elt;
- *	 void	*in_stuff;	  -- stuff to stick in the list
- *	 void	*out_stuff
- *
- *	 lst = DLNewList();				   -- make a new dllist
- *	 DLAddHead(lst, DLNewElem(in_stuff)); -- add a new element to the list
- *											 with in_stuff as the value
- *	  ...
- *	 elt = DLGetHead(lst);			   -- retrieve the head element
- *	 out_stuff = (void*)DLE_VAL(elt);  -- get the stuff out
- *	 DLRemove(elt);					   -- removes the element from its list
- *	 DLFreeElem(elt);				   -- free the element since we don't
- *										  use it anymore
- *
- *
- * It is also possible to use Dllist objects that are embedded in larger
- * structures instead of being separately malloc'd.  To do this, use
- * DLInitElem() to initialize a Dllist field within a larger object.
- * Don't forget to DLRemove() each field from its list (if any) before
- * freeing the larger object!
- *
- *
- * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * src/include/lib/dllist.h
- *
- *-------------------------------------------------------------------------
- */
-
-#ifndef DLLIST_H
-#define DLLIST_H
-
-struct Dllist;
-struct Dlelem;
-
-typedef struct Dlelem
-{
-	struct Dlelem *dle_next;	/* next element */
-	struct Dlelem *dle_prev;	/* previous element */
-	void	   *dle_val;		/* value of the element */
-	struct Dllist *dle_list;	/* what list this element is in */
-} Dlelem;
-
-typedef struct Dllist
-{
-	Dlelem	   *dll_head;
-	Dlelem	   *dll_tail;
-} Dllist;
-
-extern Dllist *DLNewList(void); /* allocate and initialize a list header */
-extern void DLInitList(Dllist *list);	/* init a header alloced by caller */
-extern void DLFreeList(Dllist *list);	/* free up a list and all the nodes in
-										 * it */
-extern Dlelem *DLNewElem(void *val);
-extern void DLInitElem(Dlelem *e, void *val);
-extern void DLFreeElem(Dlelem *e);
-extern void DLRemove(Dlelem *e);	/* removes node from list */
-extern void DLAddHead(Dllist *list, Dlelem *node);
-extern void DLAddTail(Dllist *list, Dlelem *node);
-extern Dlelem *DLRemHead(Dllist *list); /* remove and return the head */
-extern Dlelem *DLRemTail(Dllist *list);
-extern void DLMoveToFront(Dlelem *e);	/* move node to front of its list */
-
-/* These are macros for speed */
-#define DLGetHead(list)  ((list)->dll_head)
-#define DLGetTail(list)  ((list)->dll_tail)
-#define DLGetSucc(elem)  ((elem)->dle_next)
-#define DLGetPred(elem)  ((elem)->dle_prev)
-#define DLGetListHdr(elem)	((elem)->dle_list)
-
-#define DLE_VAL(elem)	((elem)->dle_val)
-
-#endif   /* DLLIST_H */
diff --git a/src/include/lib/ilist.h b/src/include/lib/ilist.h
new file mode 100644
index 00000000000..54514423358
--- /dev/null
+++ b/src/include/lib/ilist.h
@@ -0,0 +1,767 @@
+/*-------------------------------------------------------------------------
+ *
+ * ilist.h
+ *		integrated/inline doubly- and singly-linked lists
+ *
+ * This implementation is as efficient as possible: the lists don't have
+ * any memory management overhead, because the list pointers are embedded
+ * within some larger structure.
+ *
+ * There are two kinds of empty doubly linked lists: those that have been
+ * initialized to NULL, and those that have been initialized to circularity.
+ * The second kind is useful for tight optimization, because there are some
+ * operations that can be done without branches (and thus faster) on lists that
+ * have been initialized to circularity.  Most users don't care all that much,
+ * and so can skip the initialization step until really required.
+ *
+ * NOTES
+ *		This is intended to be used in situations where memory for a struct and
+ *		its contents already needs to be allocated and the overhead of
+ *		allocating extra list cells for every list element is noticeable.  Thus,
+ *		none of the functions here allocate any memory; they just manipulate
+ *		externally managed memory.	The API for singly/doubly linked lists is
+ *		identical as far as capabilities of both allow.
+ *
+ * EXAMPLES
+ *
+ * Here's a simple example demonstrating how this can be used.  Let's assume we
+ * want to store information about the tables contained in a database.
+ *
+ * #include "lib/ilist.h"
+ *
+ * // Define struct for the databases including a list header that will be used
+ * // to access the nodes in the list later on.
+ * typedef struct my_database
+ * {
+ *		char	   *datname;
+ *		dlist_head	tables;
+ *		// ...
+ * } my_database;
+ *
+ * // Define struct for the tables. Note the list_node element which stores
+ * // information about prev/next list nodes.
+ * typedef struct my_table
+ * {
+ *		char	   *tablename;
+ *		dlist_node	list_node;
+ *		perm_t		permissions;
+ *		// ...
+ * } my_table;
+ *
+ * // create a database
+ * my_database *db = create_database();
+ *
+ * // and add a few tables to its table list
+ * dlist_push_head(&db->tables, &create_table(db, "a")->list_node);
+ * ...
+ * dlist_push_head(&db->tables, &create_table(db, "b")->list_node);
+ *
+ *
+ * To iterate over the table list, we allocate an iterator element and use
+ * a specialized looping construct.  Inside a dlist_foreach, the iterator's
+ * 'cur' field can be used to access the current element.  iter.cur points to a
+ * 'dlist_node', but most of the time what we want is the actual table
+ * information; dlist_container() gives us that, like so:
+ *
+ * dlist_iter	iter;
+ * dlist_foreach(iter, &db->tables)
+ * {
+ *		my_table   *tbl = dlist_container(my_table, list_node, iter.cur);
+ *		printf("we have a table: %s in database %s\n",
+ *			   tbl->tablename, db->datname);
+ * }
+ *
+ *
+ * While a simple iteration is useful, we sometimes also want to manipulate
+ * the list while iterating.  There is a different iterator element and looping
+ * construct for that.	Suppose we want to delete tables that meet a certain
+ * criterion:
+ *
+ * dlist_mutable_iter miter;
+ * dlist_foreach_modify(miter, &db->tables)
+ * {
+ *		my_table   *tbl = dlist_container(my_table, list_node, miter.cur);
+ *
+ *		if (!tbl->to_be_deleted)
+ *			continue;		// don't touch this one
+ *
+ *		// unlink the current table from the linked list
+ *		dlist_delete(&db->tables, miter.cur);
+ *		// as these lists never manage memory, we can freely access the table
+ *		// after it's been deleted
+ *		drop_table(db, tbl);
+ * }
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/include/lib/ilist.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef ILIST_H
+#define ILIST_H
+
+/*
+ * Enable for extra debugging. This is rather expensive, so it's not enabled by
+ * default even when USE_ASSERT_CHECKING.
+ */
+/* #define ILIST_DEBUG */
+
+/*
+ * Node of a doubly linked list.
+ *
+ * Embed this in structs that need to be part of a doubly linked list.
+ */
+typedef struct dlist_node dlist_node;
+struct dlist_node
+{
+	dlist_node *prev;
+	dlist_node *next;
+};
+
+/*
+ * Head of a doubly linked list.
+ *
+ * Non-empty lists are internally circularly linked.  Circular lists have the
+ * advantage of not needing any branches in the most common list manipulations.
+ * An empty list can also be represented as a pair of NULL pointers, making
+ * initialization easier.
+ */
+typedef struct dlist_head
+{
+	/*
+	 * head->next either points to the first element of the list; to &head if
+	 * it's a circular empty list; or to NULL if empty and not circular.
+	 *
+	 * head->prev either points to the last element of the list; to &head if
+	 * it's a circular empty list; or to NULL if empty and not circular.
+	 */
+	dlist_node	head;
+} dlist_head;
+
+
+/*
+ * Doubly linked list iterator.
+ *
+ * Used as state in dlist_foreach() and dlist_reverse_foreach(). To get the
+ * current element of the iteration use the 'cur' member.
+ *
+ * Iterations using this are *not* allowed to change the list while iterating!
+ *
+ * NB: We use an extra type for this to make it possible to avoid multiple
+ * evaluations of arguments in the dlist_foreach() macro.
+ */
+typedef struct dlist_iter
+{
+	dlist_node *end;			/* last node we iterate to */
+	dlist_node *cur;			/* current element */
+} dlist_iter;
+
+/*
+ * Doubly linked list iterator allowing some modifications while iterating
+ *
+ * Used as state in dlist_foreach_modify(). To get the current element of the
+ * iteration use the 'cur' member.
+ *
+ * Iterations using this are only allowed to change the list at the current
+ * point of iteration. It is fine to delete the current node, but it is *not*
+ * fine to modify other nodes.
+ *
+ * NB: We need a separate type for mutable iterations to avoid having to pass
+ * in two iterators or some other state variable as we need to store the
+ * '->next' node of the current node so it can be deleted or modified by the
+ * user.
+ */
+typedef struct dlist_mutable_iter
+{
+	dlist_node *end;			/* last node we iterate to */
+	dlist_node *cur;			/* current element */
+	dlist_node *next;			/* next node we iterate to, so we can delete
+								 * cur */
+} dlist_mutable_iter;
+
+/*
+ * Node of a singly linked list.
+ *
+ * Embed this in structs that need to be part of a singly linked list.
+ */
+typedef struct slist_node slist_node;
+struct slist_node
+{
+	slist_node *next;
+};
+
+/*
+ * Head of a singly linked list.
+ *
+ * Singly linked lists are not circularly linked, in contrast to doubly linked
+ * lists. As no pointer to the last list element and to the previous node needs
+ * to be maintained this doesn't incur any additional branches in the usual
+ * manipulations.
+ */
+typedef struct slist_head
+{
+	slist_node	head;
+} slist_head;
+
+/*
+ * Singly linked list iterator
+ *
+ * Used in slist_foreach(). To get the current element of the iteration use the
+ * 'cur' member.
+ *
+ * Do *not* manipulate the list while iterating!
+ *
+ * NB: this wouldn't really need to be an extra struct, we could use a
+ * slist_node * directly. We still use a separate type for consistency.
+ */
+typedef struct slist_iter
+{
+	slist_node *cur;
+} slist_iter;
+
+/*
+ * Singly linked list iterator allowing some modifications while iterating
+ *
+ * Used in slist_foreach_modify.
+ *
+ * Iterations using this are allowed to remove the current node and to add more
+ * nodes to the beginning of the list.
+ */
+typedef struct slist_mutable_iter
+{
+	slist_node *cur;
+	slist_node *next;
+} slist_mutable_iter;
+
+
+/* Prototypes for functions too big to be inline */
+
+/* Attention: O(n) */
+extern void slist_delete(slist_head *head, slist_node *node);
+
+#ifdef ILIST_DEBUG
+extern void dlist_check(dlist_head *head);
+extern void slist_check(slist_head *head);
+#else
+/*
+ * These seemingly useless casts to void are here to keep the compiler quiet
+ * about the argument being unused in many functions in a non-debug compile,
+ * in which functions the only point of passing the list head pointer is to be
+ * able to run these checks.
+ */
+#define dlist_check(head)	(void) (head)
+#define slist_check(head)	(void) (head)
+#endif   /* ILIST_DEBUG */
+
+/* Static initializers */
+#define DLIST_STATIC_INIT(name) {{&name.head, &name.head}}
+#define SLIST_STATIC_INIT(name) {{NULL}}
+
+
+/*
+ * We want the functions below to be inline; but if the compiler doesn't
+ * support that, fall back on providing them as regular functions.	See
+ * STATIC_IF_INLINE in c.h.
+ */
+#ifndef PG_USE_INLINE
+extern void dlist_init(dlist_head *head);
+extern bool dlist_is_empty(dlist_head *head);
+extern void dlist_push_head(dlist_head *head, dlist_node *node);
+extern void dlist_push_tail(dlist_head *head, dlist_node *node);
+extern void dlist_insert_after(dlist_head *head,
+				   dlist_node *after, dlist_node *node);
+extern void dlist_insert_before(dlist_head *head,
+					dlist_node *before, dlist_node *node);
+extern void dlist_delete(dlist_head *head, dlist_node *node);
+extern dlist_node *dlist_pop_head_node(dlist_head *head);
+extern void dlist_move_head(dlist_head *head, dlist_node *node);
+extern bool dlist_has_next(dlist_head *head, dlist_node *node);
+extern bool dlist_has_prev(dlist_head *head, dlist_node *node);
+extern dlist_node *dlist_next_node(dlist_head *head, dlist_node *node);
+extern dlist_node *dlist_prev_node(dlist_head *head, dlist_node *node);
+extern dlist_node *dlist_head_node(dlist_head *head);
+extern dlist_node *dlist_tail_node(dlist_head *head);
+
+/* dlist macro support functions */
+extern void *dlist_tail_element_off(dlist_head *head, size_t off);
+extern void *dlist_head_element_off(dlist_head *head, size_t off);
+#endif   /* !PG_USE_INLINE */
+
+#if defined(PG_USE_INLINE) || defined(ILIST_INCLUDE_DEFINITIONS)
+/*
+ * Initialize the head of a list. Previous state will be thrown away without
+ * any cleanup.
+ */
+STATIC_IF_INLINE void
+dlist_init(dlist_head *head)
+{
+	head->head.next = head->head.prev = &head->head;
+
+	dlist_check(head);
+}
+
+/*
+ * Insert a node at the beginning of the list.
+ */
+STATIC_IF_INLINE void
+dlist_push_head(dlist_head *head, dlist_node *node)
+{
+	if (head->head.next == NULL)
+		dlist_init(head);
+
+	node->next = head->head.next;
+	node->prev = &head->head;
+	node->next->prev = node;
+	head->head.next = node;
+
+	dlist_check(head);
+}
+
+/*
+ * Inserts a node at the end of the list.
+ */
+STATIC_IF_INLINE void
+dlist_push_tail(dlist_head *head, dlist_node *node)
+{
+	if (head->head.next == NULL)
+		dlist_init(head);
+
+	node->next = &head->head;
+	node->prev = head->head.prev;
+	node->prev->next = node;
+	head->head.prev = node;
+
+	dlist_check(head);
+}
+
+/*
+ * Insert a node after another *in the same list*
+ */
+STATIC_IF_INLINE void
+dlist_insert_after(dlist_head *head, dlist_node *after, dlist_node *node)
+{
+	dlist_check(head);
+	/* XXX: assert 'after' is in 'head'? */
+
+	node->prev = after;
+	node->next = after->next;
+	after->next = node;
+	node->next->prev = node;
+
+	dlist_check(head);
+}
+
+/*
+ * Insert a node before another *in the same list*
+ */
+STATIC_IF_INLINE void
+dlist_insert_before(dlist_head *head, dlist_node *before, dlist_node *node)
+{
+	dlist_check(head);
+	/* XXX: assert 'before' is in 'head'? */
+
+	node->prev = before->prev;
+	node->next = before;
+	before->prev = node;
+	node->prev->next = node;
+
+	dlist_check(head);
+}
+
+/*
+ * Delete 'node' from list.
+ *
+ * It is not allowed to delete a 'node' which is is not in the list 'head'
+ */
+STATIC_IF_INLINE void
+dlist_delete(dlist_head *head, dlist_node *node)
+{
+	dlist_check(head);
+
+	node->prev->next = node->next;
+	node->next->prev = node->prev;
+
+	dlist_check(head);
+}
+
+/*
+ * Delete and return the first node from a list.
+ *
+ * Undefined behaviour when the list is empty.	Check with dlist_is_empty if
+ * necessary.
+ */
+STATIC_IF_INLINE dlist_node *
+dlist_pop_head_node(dlist_head *head)
+{
+	dlist_node *ret;
+
+	Assert(&head->head != head->head.next);
+
+	ret = head->head.next;
+	dlist_delete(head, head->head.next);
+	return ret;
+}
+
+/*
+ * Move element from its current position in the list to the head position in
+ * the same list.
+ *
+ * Undefined behaviour if 'node' is not already part of the list.
+ */
+STATIC_IF_INLINE void
+dlist_move_head(dlist_head *head, dlist_node *node)
+{
+	/* fast path if it's already at the head */
+	if (head->head.next == node)
+		return;
+
+	dlist_delete(head, node);
+	dlist_push_head(head, node);
+
+	dlist_check(head);
+}
+
+/*
+ * Check whether the passed node is the last element in the list.
+ */
+STATIC_IF_INLINE bool
+dlist_has_next(dlist_head *head, dlist_node *node)
+{
+	return node->next != &head->head;
+}
+
+/*
+ * Check whether the passed node is the first element in the list.
+ */
+STATIC_IF_INLINE bool
+dlist_has_prev(dlist_head *head, dlist_node *node)
+{
+	return node->prev != &head->head;
+}
+
+/*
+ * Return the next node in the list.
+ *
+ * Undefined behaviour when no next node exists.  Use dlist_has_next to make
+ * sure.
+ */
+STATIC_IF_INLINE dlist_node *
+dlist_next_node(dlist_head *head, dlist_node *node)
+{
+	Assert(dlist_has_next(head, node));
+	return node->next;
+}
+
+/*
+ * Return previous node in the list.
+ *
+ * Undefined behaviour when no prev node exists.  Use dlist_has_prev to make
+ * sure.
+ */
+STATIC_IF_INLINE dlist_node *
+dlist_prev_node(dlist_head *head, dlist_node *node)
+{
+	Assert(dlist_has_prev(head, node));
+	return node->prev;
+}
+
+/*
+ * Return whether the list is empty.
+ *
+ * An empty list has either its first 'next' pointer set to NULL, or to itself.
+ */
+STATIC_IF_INLINE bool
+dlist_is_empty(dlist_head *head)
+{
+	dlist_check(head);
+
+	return head->head.next == NULL || head->head.next == &(head->head);
+}
+
+/* internal support function */
+STATIC_IF_INLINE void *
+dlist_head_element_off(dlist_head *head, size_t off)
+{
+	Assert(!dlist_is_empty(head));
+	return (char *) head->head.next - off;
+}
+
+/*
+ * Return the first node in the list.
+ *
+ * Use dlist_is_empty to make sure the list is not empty if not sure.
+ */
+STATIC_IF_INLINE dlist_node *
+dlist_head_node(dlist_head *head)
+{
+	return dlist_head_element_off(head, 0);
+}
+
+/* internal support function */
+STATIC_IF_INLINE void *
+dlist_tail_element_off(dlist_head *head, size_t off)
+{
+	Assert(!dlist_is_empty(head));
+	return (char *) head->head.prev - off;
+}
+
+/*
+ * Return the last node in the list.
+ *
+ * Use dlist_is_empty to make sure the list is not empty if not sure.
+ */
+STATIC_IF_INLINE dlist_node *
+dlist_tail_node(dlist_head *head)
+{
+	return dlist_tail_element_off(head, 0);
+}
+#endif   /* PG_USE_INLINE || ILIST_INCLUDE_DEFINITIONS */
+
+/*
+ * Return the containing struct of 'type' where 'membername' is the dlist_node
+ * pointed at by 'ptr'.
+ *
+ * This is used to convert a dlist_node * back to its containing struct.
+ *
+ * Note that AssertVariableIsOfTypeMacro is a compile-time only check, so we
+ * don't have multiple evaluation dangers here.
+ */
+#define dlist_container(type, membername, ptr)								\
+	(AssertVariableIsOfTypeMacro(ptr, dlist_node *),						\
+	 AssertVariableIsOfTypeMacro(((type *) NULL)->membername, dlist_node),	\
+	 ((type *)((char *)(ptr) - offsetof(type, membername))))
+
+/*
+ * Return the value of first element in the list.
+ *
+ * The list must not be empty.
+ *
+ * Note that AssertVariableIsOfTypeMacro is a compile-time only check, so we
+ * don't have multiple evaluation dangers here.
+ */
+#define dlist_head_element(type, membername, ptr)							\
+	(AssertVariableIsOfTypeMacro(((type *) NULL)->membername, dlist_node),	\
+	 ((type *)dlist_head_element_off(ptr, offsetof(type, membername))))
+
+/*
+ * Return the value of first element in the list.
+ *
+ * The list must not be empty.
+ *
+ * Note that AssertVariableIsOfTypeMacro is a compile-time only check, so we
+ * don't have multiple evaluation dangers here.
+ */
+#define dlist_tail_element(type, membername, ptr)							\
+	(AssertVariableIsOfTypeMacro(((type *) NULL)->membername, dlist_node),	\
+	 ((type *)dlist_tail_element_off(ptr, offsetof(type, membername))))
+
+/*
+ * Iterate through the list pointed at by 'ptr' storing the state in 'iter'.
+ *
+ * Access the current element with iter.cur.
+ *
+ * It is *not* allowed to manipulate the list during iteration.
+ */
+#define dlist_foreach(iter, ptr)											\
+	AssertVariableIsOfType(iter, dlist_iter);								\
+	AssertVariableIsOfType(ptr, dlist_head *);								\
+	for (iter.end = &(ptr)->head,											\
+		 	iter.cur = iter.end->next ? iter.end->next : iter.end;			\
+		 iter.cur != iter.end;												\
+		 iter.cur = iter.cur->next)
+
+/*
+ * Iterate through the list pointed at by 'ptr' storing the state in 'iter'.
+ *
+ * Access the current element with iter.cur.
+ *
+ * It is allowed to delete the current element from the list. Every other
+ * manipulation can lead to corruption.
+ */
+#define dlist_foreach_modify(iter, ptr)										\
+	AssertVariableIsOfType(iter, dlist_mutable_iter);						\
+	AssertVariableIsOfType(ptr, dlist_head *);								\
+	for (iter.end = &(ptr)->head,											\
+			 iter.cur = iter.end->next ? iter.end->next : iter.end,			\
+			 iter.next = iter.cur->next;									\
+		 iter.cur != iter.end;												\
+		 iter.cur = iter.next, iter.next = iter.cur->next)
+
+/*
+ * Iterate through the list in reverse order.
+ *
+ * It is *not* allowed to manipulate the list during iteration.
+ */
+#define dlist_reverse_foreach(iter, ptr)									\
+	AssertVariableIsOfType(iter, dlist_iter);								\
+	AssertVariableIsOfType(ptr, dlist_head *);								\
+	for (iter.end = &(ptr)->head,											\
+			 iter.cur = iter.end->prev ? iter.end->prev : iter.end;			\
+		 iter.cur != iter.end;												\
+		 iter.cur = iter.cur->prev)
+
+
+/*
+ * We want the functions below to be inline; but if the compiler doesn't
+ * support that, fall back on providing them as regular functions.	See
+ * STATIC_IF_INLINE in c.h.
+ */
+#ifndef PG_USE_INLINE
+extern void slist_init(slist_head *head);
+extern bool slist_is_empty(slist_head *head);
+extern slist_node *slist_head_node(slist_head *head);
+extern void slist_push_head(slist_head *head, slist_node *node);
+extern slist_node *slist_pop_head_node(slist_head *head);
+extern void slist_insert_after(slist_head *head,
+				   slist_node *after, slist_node *node);
+extern bool slist_has_next(slist_head *head, slist_node *node);
+extern slist_node *slist_next_node(slist_head *head, slist_node *node);
+
+/* slist macro support function */
+extern void *slist_head_element_off(slist_head *head, size_t off);
+#endif
+
+#if defined(PG_USE_INLINE) || defined(ILIST_INCLUDE_DEFINITIONS)
+/*
+ * Initialize a singly linked list.
+ */
+STATIC_IF_INLINE void
+slist_init(slist_head *head)
+{
+	head->head.next = NULL;
+
+	slist_check(head);
+}
+
+/*
+ * Is the list empty?
+ */
+STATIC_IF_INLINE bool
+slist_is_empty(slist_head *head)
+{
+	slist_check(head);
+
+	return head->head.next == NULL;
+}
+
+/* internal support function */
+STATIC_IF_INLINE void *
+slist_head_element_off(slist_head *head, size_t off)
+{
+	Assert(!slist_is_empty(head));
+	return (char *) head->head.next - off;
+}
+
+/*
+ * Push 'node' as the new first node in the list, pushing the original head to
+ * the second position.
+ */
+STATIC_IF_INLINE void
+slist_push_head(slist_head *head, slist_node *node)
+{
+	node->next = head->head.next;
+	head->head.next = node;
+
+	slist_check(head);
+}
+
+/*
+ * Remove and return the first node in the list
+ *
+ * Undefined behaviour if the list is empty.
+ */
+STATIC_IF_INLINE slist_node *
+slist_pop_head_node(slist_head *head)
+{
+	slist_node *node;
+
+	Assert(!slist_is_empty(head));
+
+	node = head->head.next;
+	head->head.next = head->head.next->next;
+
+	slist_check(head);
+
+	return node;
+}
+
+/*
+ * Insert a new node after another one
+ *
+ * Undefined behaviour if 'after' is not part of the list already.
+ */
+STATIC_IF_INLINE void
+slist_insert_after(slist_head *head, slist_node *after,
+				   slist_node *node)
+{
+	node->next = after->next;
+	after->next = node;
+
+	slist_check(head);
+}
+
+/*
+ * Return whether 'node' has a following node
+ */
+STATIC_IF_INLINE bool
+slist_has_next(slist_head *head,
+			   slist_node *node)
+{
+	slist_check(head);
+
+	return node->next != NULL;
+}
+#endif   /* PG_USE_INLINE || ILIST_INCLUDE_DEFINITIONS */
+
+/*
+ * Return the containing struct of 'type' where 'membername' is the slist_node
+ * pointed at by 'ptr'.
+ *
+ * This is used to convert a slist_node * back to its containing struct.
+ *
+ * Note that AssertVariableIsOfTypeMacro is a compile-time only check, so we
+ * don't have multiple evaluation dangers here.
+ */
+#define slist_container(type, membername, ptr)								\
+	(AssertVariableIsOfTypeMacro(ptr, slist_node *),						\
+	 AssertVariableIsOfTypeMacro(((type *) NULL)->membername, slist_node),	\
+	 ((type *)((char *)(ptr) - offsetof(type, membername))))
+
+/*
+ * Return the value of first element in the list.
+ */
+#define slist_head_element(type, membername, ptr)							\
+	(AssertVariableIsOfTypeMacro(((type *) NULL)->membername, slist_node),	\
+	 slist_head_element_off(ptr, offsetoff(type, membername)))
+
+/*
+ * Iterate through the list 'ptr' using the iterator 'iter'.
+ *
+ * It is *not* allowed to manipulate the list during iteration.
+ */
+#define slist_foreach(iter, ptr)											\
+	AssertVariableIsOfType(iter, slist_iter);								\
+	AssertVariableIsOfType(ptr, slist_head *);								\
+	for (iter.cur = (ptr)->head.next;										\
+		 iter.cur != NULL;													\
+		 iter.cur = iter.cur->next)
+
+/*
+ * Iterate through the list 'ptr' using the iterator 'iter' allowing some
+ * modifications.
+ *
+ * It is allowed to delete the current element from the list and add new nodes
+ * before the current position. Other manipulations can lead to corruption.
+ */
+#define slist_foreach_modify(iter, ptr)										\
+	AssertVariableIsOfType(iter, slist_mutable_iter);						\
+	AssertVariableIsOfType(ptr, slist_head *);								\
+	for (iter.cur = (ptr)->head.next,										\
+			 iter.next = iter.cur ? iter.cur->next : NULL;					\
+		iter.cur != NULL;													\
+		iter.cur = iter.next,												\
+			 iter.next = iter.next ? iter.next->next : NULL)
+
+#endif   /* ILIST_H */